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Can compressed videos be decoded back to their uncompresed original format?


What are the differences of watching a 1080p and a 720p version of the same media on a 720p screen?Can someone suggest a workflow for transcoding videos in iPhoto from Motion-JPEG to something smaller?Problems with frame rate on video conversion using ffmpeg with libx264Converting RAW Blackmagic Intensity Card framesExtract Y-channel of every I-frame from MPEG4 movie as loslessly as possibleffmpeg segment by video-time instead of wall-timeMerging two videos while skipping common partsUsing a lossless video codec for archiving (monochrome) scientific video dataAdapting video for LaTeX with ffmpeg does not produce the expected resultFFmpeg filter for scene changeCan ffmpeg be used to reduce encoded file size back to original after OBS+VLC workflow?






.everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty height:90px;width:728px;box-sizing:border-box;








15















The following is mentioned in the ffmpeg documentation.




ffmpeg calls the libavformat library (containing demuxers) to read
input files and get packets containing encoded data from them...
Encoded packets are then passed to the decoder... The decoder produces
uncompressed frames (raw video/PCM audio/...) which can be processed
further by filtering...




Does that mean that you can always extract the original large size videos from all the compressed formats/codecs like h.264?










share|improve this question









New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.















  • 17





    uncompressed != original

    – Bergi
    2 days ago











  • Yeah, and the question is about reversing the uncompressed to it's original; which has been explained and discussed in the answers.

    – mjustin
    yesterday






  • 2





    Aside from the technically oriented answers, a legally oriented person (a lawyer or judge or possibly the owner of the intellectual property) will, most probably, insist that the decompressed video is, in a nutshell, still the original work (even if it's copied at a much lower resolution/quality, for example).

    – Klaws
    yesterday











  • @Klaws It logically makes sense. But anyway, one cannot legitimately redistribute the video/audio in an opensource format unless the original allows it to be converted or redistributed; as far as I know.

    – mjustin
    yesterday

















15















The following is mentioned in the ffmpeg documentation.




ffmpeg calls the libavformat library (containing demuxers) to read
input files and get packets containing encoded data from them...
Encoded packets are then passed to the decoder... The decoder produces
uncompressed frames (raw video/PCM audio/...) which can be processed
further by filtering...




Does that mean that you can always extract the original large size videos from all the compressed formats/codecs like h.264?










share|improve this question









New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.















  • 17





    uncompressed != original

    – Bergi
    2 days ago











  • Yeah, and the question is about reversing the uncompressed to it's original; which has been explained and discussed in the answers.

    – mjustin
    yesterday






  • 2





    Aside from the technically oriented answers, a legally oriented person (a lawyer or judge or possibly the owner of the intellectual property) will, most probably, insist that the decompressed video is, in a nutshell, still the original work (even if it's copied at a much lower resolution/quality, for example).

    – Klaws
    yesterday











  • @Klaws It logically makes sense. But anyway, one cannot legitimately redistribute the video/audio in an opensource format unless the original allows it to be converted or redistributed; as far as I know.

    – mjustin
    yesterday













15












15








15


4






The following is mentioned in the ffmpeg documentation.




ffmpeg calls the libavformat library (containing demuxers) to read
input files and get packets containing encoded data from them...
Encoded packets are then passed to the decoder... The decoder produces
uncompressed frames (raw video/PCM audio/...) which can be processed
further by filtering...




Does that mean that you can always extract the original large size videos from all the compressed formats/codecs like h.264?










share|improve this question









New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.












The following is mentioned in the ffmpeg documentation.




ffmpeg calls the libavformat library (containing demuxers) to read
input files and get packets containing encoded data from them...
Encoded packets are then passed to the decoder... The decoder produces
uncompressed frames (raw video/PCM audio/...) which can be processed
further by filtering...




Does that mean that you can always extract the original large size videos from all the compressed formats/codecs like h.264?







video ffmpeg compression






share|improve this question









New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.











share|improve this question









New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









share|improve this question




share|improve this question








edited yesterday







mjustin













New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.









asked 2 days ago









mjustinmjustin

8715




8715




New contributor




mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.





New contributor





mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.






mjustin is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.







  • 17





    uncompressed != original

    – Bergi
    2 days ago











  • Yeah, and the question is about reversing the uncompressed to it's original; which has been explained and discussed in the answers.

    – mjustin
    yesterday






  • 2





    Aside from the technically oriented answers, a legally oriented person (a lawyer or judge or possibly the owner of the intellectual property) will, most probably, insist that the decompressed video is, in a nutshell, still the original work (even if it's copied at a much lower resolution/quality, for example).

    – Klaws
    yesterday











  • @Klaws It logically makes sense. But anyway, one cannot legitimately redistribute the video/audio in an opensource format unless the original allows it to be converted or redistributed; as far as I know.

    – mjustin
    yesterday












  • 17





    uncompressed != original

    – Bergi
    2 days ago











  • Yeah, and the question is about reversing the uncompressed to it's original; which has been explained and discussed in the answers.

    – mjustin
    yesterday






  • 2





    Aside from the technically oriented answers, a legally oriented person (a lawyer or judge or possibly the owner of the intellectual property) will, most probably, insist that the decompressed video is, in a nutshell, still the original work (even if it's copied at a much lower resolution/quality, for example).

    – Klaws
    yesterday











  • @Klaws It logically makes sense. But anyway, one cannot legitimately redistribute the video/audio in an opensource format unless the original allows it to be converted or redistributed; as far as I know.

    – mjustin
    yesterday







17




17





uncompressed != original

– Bergi
2 days ago





uncompressed != original

– Bergi
2 days ago













Yeah, and the question is about reversing the uncompressed to it's original; which has been explained and discussed in the answers.

– mjustin
yesterday





Yeah, and the question is about reversing the uncompressed to it's original; which has been explained and discussed in the answers.

– mjustin
yesterday




2




2





Aside from the technically oriented answers, a legally oriented person (a lawyer or judge or possibly the owner of the intellectual property) will, most probably, insist that the decompressed video is, in a nutshell, still the original work (even if it's copied at a much lower resolution/quality, for example).

– Klaws
yesterday





Aside from the technically oriented answers, a legally oriented person (a lawyer or judge or possibly the owner of the intellectual property) will, most probably, insist that the decompressed video is, in a nutshell, still the original work (even if it's copied at a much lower resolution/quality, for example).

– Klaws
yesterday













@Klaws It logically makes sense. But anyway, one cannot legitimately redistribute the video/audio in an opensource format unless the original allows it to be converted or redistributed; as far as I know.

– mjustin
yesterday





@Klaws It logically makes sense. But anyway, one cannot legitimately redistribute the video/audio in an opensource format unless the original allows it to be converted or redistributed; as far as I know.

– mjustin
yesterday










4 Answers
4






active

oldest

votes


















46














Video compression is typically "lossy", in contrast to "lossless".



This means that by compressing the data, and subsequently decompressing it, you end up with an approximation of the original that is (hopefully) acceptable for the purpose.



Storing images and video using lossy compression techniques is generally fine, because humans aren't very good at perceiving the detail in an image - for example, our brain can fill in lots of details from context alone (as our eyes only have a small area in the center that is of "high resolution"), and our eyes are more sensitive to the intensity of green than red or blue (which explains the allocation in RGB565).



So, when you say:




Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




You're asking one question, but leaving lots of openings for misinterpretation.



  • Can we extract the original, pixel-perfect image from a video compressed using lossy techniques?

    • No


  • Can we extract a single frame of a video compressed using lossy techniques that has high quality, and could be used as a static image?


    • Probably not - movement in a scene will cause a higher number of artifacts, while a static scene will typically look better and better over time.


  • Can we extract an image of the original size, that looks "reasonable" to a human?


    • Yes - for a given definition of "reasonable"



This imperfect resulting image will have "Compression Artifacts". As shown in the exaggerated examples below:



good / 100% JPEG



bad / 5% JPEG




As the comments have also focused heavily on Audio quality, the exact same thing occurs. However, audio is a significantly lower bandwidth medium, which allows for lossless codecs to be practical (for example FLAC).



Converting from PCM / WAV → MP3 → PCM will result in an output PCM file that has the artifacts introduced by the MP3 encode/decode process - these cannot be removed.



Additionally, concatenating codecs will allow each to introduce their own artifacts, and the order that the codecs are applied can have a significant effect on the output.



Converting PCM → MP3 → OGG vorbis → Opus is not the same as PCM → Opus, because each of the intermediary codecs are lossy.



I've made an example audio file which presents this as another exaggerated example. This is the first ~30 seconds of "Tonight" by "The 69 Eyes", alternating every 5 seconds between the following chains:



  • CD → FLAC → Opus

  • CD → FLAC → MP3 → Vorbis → Opus

The effect here is dramatic, with the higher frequencies (i.e: high-hat) being almost completely removed from the audio, and with significant channel (left/right) interaction that is especially noticeable at the beginning.



compare






share|improve this answer

























  • Comments are not for extended discussion; this conversation has been moved to chat.

    – DavidPostill
    2 days ago






  • 4





    re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

    – Peter Cordes
    yesterday






  • 3





    @opa US vs UK spelling differences do not merit editing.

    – mbrig
    yesterday


















15














A short answer for codecs in general:

Any lossless codec like FLAC or ZIP can be reversed exactly.

Any lossy codec like JPEG or MP3 cannot be reversed exactly.



This principle is also valid for video codecs.

Here HuffYUV is an example for a lossless video-codec.

And x264 is an example for a lossy video-codec.






share|improve this answer




















  • 1





    Very nicely put.

    – mjustin
    yesterday






  • 1





    To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

    – llogan
    yesterday











  • @llogan: Thank you for your clarification, it is surely helpful.

    – zx485
    yesterday











  • There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

    – Marc.2377
    22 hours ago












  • @Marc.2377: That's interesting, but as you said, it's an exception.

    – zx485
    4 hours ago


















4















Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




No. You're misinterpreting that sentence.



You can't display compressed image, just as you can't read compressed text or read file compressed with ZIP without unpacking it first. To display any image, you have to somehow represent it uncompressed in memory, pixel-for-pixel.



This doesn't imply that the uncompressed image will be identical to original - this depends on codecs used. As far as I know there are no commonly used lossless codecs. Lossy codecs aim to represent original closely enough to make the uncompressed video indistinguishable under normal circumstances, ie. when played at predicted resolution and framerate. When looking at compressed stills (ie. framerate=0) you will certainly see artifacts, unless bitrate during compression is set impractically high (ie. producing too large output files) (this answer of mine is somehow related).




By the way, MP4 is only a file format, ie. it tells you how compressed data is stored in a file, but doesn't determine how it was compressed. MP4 can work with a variety of codecs. H.264 is probably the most popular video codec used with MP4, but don't quote me on that. Audio is usually compressed with AAC, I guess.






share|improve this answer

























  • @Attie Now bold "original"

    – Lightness Races in Orbit
    yesterday






  • 1





    @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

    – gronostaj
    yesterday











  • Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

    – mjustin
    yesterday












  • @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

    – gronostaj
    yesterday











  • @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

    – mjustin
    yesterday


















1














This is a very common blunder.



You can convert from a lossy format to a lossless format, but the damage is done.



The lossless output file will show all the damage (compromised details, added artifacts) that are the reason you don't like the lossy format. You can't get that back.



The only option is to contact the publisher and see if he still has the original lossless files, and would be willing to somehow upload them to you.



There's no such thing as an Enhance button. warning: TVtropes






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    4 Answers
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    active

    oldest

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    4 Answers
    4






    active

    oldest

    votes









    active

    oldest

    votes






    active

    oldest

    votes









    46














    Video compression is typically "lossy", in contrast to "lossless".



    This means that by compressing the data, and subsequently decompressing it, you end up with an approximation of the original that is (hopefully) acceptable for the purpose.



    Storing images and video using lossy compression techniques is generally fine, because humans aren't very good at perceiving the detail in an image - for example, our brain can fill in lots of details from context alone (as our eyes only have a small area in the center that is of "high resolution"), and our eyes are more sensitive to the intensity of green than red or blue (which explains the allocation in RGB565).



    So, when you say:




    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    You're asking one question, but leaving lots of openings for misinterpretation.



    • Can we extract the original, pixel-perfect image from a video compressed using lossy techniques?

      • No


    • Can we extract a single frame of a video compressed using lossy techniques that has high quality, and could be used as a static image?


      • Probably not - movement in a scene will cause a higher number of artifacts, while a static scene will typically look better and better over time.


    • Can we extract an image of the original size, that looks "reasonable" to a human?


      • Yes - for a given definition of "reasonable"



    This imperfect resulting image will have "Compression Artifacts". As shown in the exaggerated examples below:



    good / 100% JPEG



    bad / 5% JPEG




    As the comments have also focused heavily on Audio quality, the exact same thing occurs. However, audio is a significantly lower bandwidth medium, which allows for lossless codecs to be practical (for example FLAC).



    Converting from PCM / WAV → MP3 → PCM will result in an output PCM file that has the artifacts introduced by the MP3 encode/decode process - these cannot be removed.



    Additionally, concatenating codecs will allow each to introduce their own artifacts, and the order that the codecs are applied can have a significant effect on the output.



    Converting PCM → MP3 → OGG vorbis → Opus is not the same as PCM → Opus, because each of the intermediary codecs are lossy.



    I've made an example audio file which presents this as another exaggerated example. This is the first ~30 seconds of "Tonight" by "The 69 Eyes", alternating every 5 seconds between the following chains:



    • CD → FLAC → Opus

    • CD → FLAC → MP3 → Vorbis → Opus

    The effect here is dramatic, with the higher frequencies (i.e: high-hat) being almost completely removed from the audio, and with significant channel (left/right) interaction that is especially noticeable at the beginning.



    compare






    share|improve this answer

























    • Comments are not for extended discussion; this conversation has been moved to chat.

      – DavidPostill
      2 days ago






    • 4





      re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

      – Peter Cordes
      yesterday






    • 3





      @opa US vs UK spelling differences do not merit editing.

      – mbrig
      yesterday















    46














    Video compression is typically "lossy", in contrast to "lossless".



    This means that by compressing the data, and subsequently decompressing it, you end up with an approximation of the original that is (hopefully) acceptable for the purpose.



    Storing images and video using lossy compression techniques is generally fine, because humans aren't very good at perceiving the detail in an image - for example, our brain can fill in lots of details from context alone (as our eyes only have a small area in the center that is of "high resolution"), and our eyes are more sensitive to the intensity of green than red or blue (which explains the allocation in RGB565).



    So, when you say:




    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    You're asking one question, but leaving lots of openings for misinterpretation.



    • Can we extract the original, pixel-perfect image from a video compressed using lossy techniques?

      • No


    • Can we extract a single frame of a video compressed using lossy techniques that has high quality, and could be used as a static image?


      • Probably not - movement in a scene will cause a higher number of artifacts, while a static scene will typically look better and better over time.


    • Can we extract an image of the original size, that looks "reasonable" to a human?


      • Yes - for a given definition of "reasonable"



    This imperfect resulting image will have "Compression Artifacts". As shown in the exaggerated examples below:



    good / 100% JPEG



    bad / 5% JPEG




    As the comments have also focused heavily on Audio quality, the exact same thing occurs. However, audio is a significantly lower bandwidth medium, which allows for lossless codecs to be practical (for example FLAC).



    Converting from PCM / WAV → MP3 → PCM will result in an output PCM file that has the artifacts introduced by the MP3 encode/decode process - these cannot be removed.



    Additionally, concatenating codecs will allow each to introduce their own artifacts, and the order that the codecs are applied can have a significant effect on the output.



    Converting PCM → MP3 → OGG vorbis → Opus is not the same as PCM → Opus, because each of the intermediary codecs are lossy.



    I've made an example audio file which presents this as another exaggerated example. This is the first ~30 seconds of "Tonight" by "The 69 Eyes", alternating every 5 seconds between the following chains:



    • CD → FLAC → Opus

    • CD → FLAC → MP3 → Vorbis → Opus

    The effect here is dramatic, with the higher frequencies (i.e: high-hat) being almost completely removed from the audio, and with significant channel (left/right) interaction that is especially noticeable at the beginning.



    compare






    share|improve this answer

























    • Comments are not for extended discussion; this conversation has been moved to chat.

      – DavidPostill
      2 days ago






    • 4





      re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

      – Peter Cordes
      yesterday






    • 3





      @opa US vs UK spelling differences do not merit editing.

      – mbrig
      yesterday













    46












    46








    46







    Video compression is typically "lossy", in contrast to "lossless".



    This means that by compressing the data, and subsequently decompressing it, you end up with an approximation of the original that is (hopefully) acceptable for the purpose.



    Storing images and video using lossy compression techniques is generally fine, because humans aren't very good at perceiving the detail in an image - for example, our brain can fill in lots of details from context alone (as our eyes only have a small area in the center that is of "high resolution"), and our eyes are more sensitive to the intensity of green than red or blue (which explains the allocation in RGB565).



    So, when you say:




    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    You're asking one question, but leaving lots of openings for misinterpretation.



    • Can we extract the original, pixel-perfect image from a video compressed using lossy techniques?

      • No


    • Can we extract a single frame of a video compressed using lossy techniques that has high quality, and could be used as a static image?


      • Probably not - movement in a scene will cause a higher number of artifacts, while a static scene will typically look better and better over time.


    • Can we extract an image of the original size, that looks "reasonable" to a human?


      • Yes - for a given definition of "reasonable"



    This imperfect resulting image will have "Compression Artifacts". As shown in the exaggerated examples below:



    good / 100% JPEG



    bad / 5% JPEG




    As the comments have also focused heavily on Audio quality, the exact same thing occurs. However, audio is a significantly lower bandwidth medium, which allows for lossless codecs to be practical (for example FLAC).



    Converting from PCM / WAV → MP3 → PCM will result in an output PCM file that has the artifacts introduced by the MP3 encode/decode process - these cannot be removed.



    Additionally, concatenating codecs will allow each to introduce their own artifacts, and the order that the codecs are applied can have a significant effect on the output.



    Converting PCM → MP3 → OGG vorbis → Opus is not the same as PCM → Opus, because each of the intermediary codecs are lossy.



    I've made an example audio file which presents this as another exaggerated example. This is the first ~30 seconds of "Tonight" by "The 69 Eyes", alternating every 5 seconds between the following chains:



    • CD → FLAC → Opus

    • CD → FLAC → MP3 → Vorbis → Opus

    The effect here is dramatic, with the higher frequencies (i.e: high-hat) being almost completely removed from the audio, and with significant channel (left/right) interaction that is especially noticeable at the beginning.



    compare






    share|improve this answer















    Video compression is typically "lossy", in contrast to "lossless".



    This means that by compressing the data, and subsequently decompressing it, you end up with an approximation of the original that is (hopefully) acceptable for the purpose.



    Storing images and video using lossy compression techniques is generally fine, because humans aren't very good at perceiving the detail in an image - for example, our brain can fill in lots of details from context alone (as our eyes only have a small area in the center that is of "high resolution"), and our eyes are more sensitive to the intensity of green than red or blue (which explains the allocation in RGB565).



    So, when you say:




    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    You're asking one question, but leaving lots of openings for misinterpretation.



    • Can we extract the original, pixel-perfect image from a video compressed using lossy techniques?

      • No


    • Can we extract a single frame of a video compressed using lossy techniques that has high quality, and could be used as a static image?


      • Probably not - movement in a scene will cause a higher number of artifacts, while a static scene will typically look better and better over time.


    • Can we extract an image of the original size, that looks "reasonable" to a human?


      • Yes - for a given definition of "reasonable"



    This imperfect resulting image will have "Compression Artifacts". As shown in the exaggerated examples below:



    good / 100% JPEG



    bad / 5% JPEG




    As the comments have also focused heavily on Audio quality, the exact same thing occurs. However, audio is a significantly lower bandwidth medium, which allows for lossless codecs to be practical (for example FLAC).



    Converting from PCM / WAV → MP3 → PCM will result in an output PCM file that has the artifacts introduced by the MP3 encode/decode process - these cannot be removed.



    Additionally, concatenating codecs will allow each to introduce their own artifacts, and the order that the codecs are applied can have a significant effect on the output.



    Converting PCM → MP3 → OGG vorbis → Opus is not the same as PCM → Opus, because each of the intermediary codecs are lossy.



    I've made an example audio file which presents this as another exaggerated example. This is the first ~30 seconds of "Tonight" by "The 69 Eyes", alternating every 5 seconds between the following chains:



    • CD → FLAC → Opus

    • CD → FLAC → MP3 → Vorbis → Opus

    The effect here is dramatic, with the higher frequencies (i.e: high-hat) being almost completely removed from the audio, and with significant channel (left/right) interaction that is especially noticeable at the beginning.



    compare







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited yesterday









    Cody

    1032




    1032










    answered 2 days ago









    AttieAttie

    12.8k43547




    12.8k43547












    • Comments are not for extended discussion; this conversation has been moved to chat.

      – DavidPostill
      2 days ago






    • 4





      re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

      – Peter Cordes
      yesterday






    • 3





      @opa US vs UK spelling differences do not merit editing.

      – mbrig
      yesterday

















    • Comments are not for extended discussion; this conversation has been moved to chat.

      – DavidPostill
      2 days ago






    • 4





      re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

      – Peter Cordes
      yesterday






    • 3





      @opa US vs UK spelling differences do not merit editing.

      – mbrig
      yesterday
















    Comments are not for extended discussion; this conversation has been moved to chat.

    – DavidPostill
    2 days ago





    Comments are not for extended discussion; this conversation has been moved to chat.

    – DavidPostill
    2 days ago




    4




    4





    re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

    – Peter Cordes
    yesterday





    re: chaining lossy codecs: The easiest way to understand this is that artefacts introduced by the first lossy codec become part of the "details" that the 2nd codec has to spend bits accurately reproducing. Any post-processing (like h.264's in-loop deblocking filter), or feeding one codec to another code, will smear out the ringing / blocking so it doesn't just become easy-to-quantize input for the next codec. (Like might happen with simple jpg -> jpg -> jpg or other simple codecs where stability might be reached.)

    – Peter Cordes
    yesterday




    3




    3





    @opa US vs UK spelling differences do not merit editing.

    – mbrig
    yesterday





    @opa US vs UK spelling differences do not merit editing.

    – mbrig
    yesterday













    15














    A short answer for codecs in general:

    Any lossless codec like FLAC or ZIP can be reversed exactly.

    Any lossy codec like JPEG or MP3 cannot be reversed exactly.



    This principle is also valid for video codecs.

    Here HuffYUV is an example for a lossless video-codec.

    And x264 is an example for a lossy video-codec.






    share|improve this answer




















    • 1





      Very nicely put.

      – mjustin
      yesterday






    • 1





      To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

      – llogan
      yesterday











    • @llogan: Thank you for your clarification, it is surely helpful.

      – zx485
      yesterday











    • There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

      – Marc.2377
      22 hours ago












    • @Marc.2377: That's interesting, but as you said, it's an exception.

      – zx485
      4 hours ago















    15














    A short answer for codecs in general:

    Any lossless codec like FLAC or ZIP can be reversed exactly.

    Any lossy codec like JPEG or MP3 cannot be reversed exactly.



    This principle is also valid for video codecs.

    Here HuffYUV is an example for a lossless video-codec.

    And x264 is an example for a lossy video-codec.






    share|improve this answer




















    • 1





      Very nicely put.

      – mjustin
      yesterday






    • 1





      To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

      – llogan
      yesterday











    • @llogan: Thank you for your clarification, it is surely helpful.

      – zx485
      yesterday











    • There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

      – Marc.2377
      22 hours ago












    • @Marc.2377: That's interesting, but as you said, it's an exception.

      – zx485
      4 hours ago













    15












    15








    15







    A short answer for codecs in general:

    Any lossless codec like FLAC or ZIP can be reversed exactly.

    Any lossy codec like JPEG or MP3 cannot be reversed exactly.



    This principle is also valid for video codecs.

    Here HuffYUV is an example for a lossless video-codec.

    And x264 is an example for a lossy video-codec.






    share|improve this answer















    A short answer for codecs in general:

    Any lossless codec like FLAC or ZIP can be reversed exactly.

    Any lossy codec like JPEG or MP3 cannot be reversed exactly.



    This principle is also valid for video codecs.

    Here HuffYUV is an example for a lossless video-codec.

    And x264 is an example for a lossy video-codec.







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited yesterday









    Solomon Ucko

    1013




    1013










    answered 2 days ago









    zx485zx485

    1,3671914




    1,3671914







    • 1





      Very nicely put.

      – mjustin
      yesterday






    • 1





      To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

      – llogan
      yesterday











    • @llogan: Thank you for your clarification, it is surely helpful.

      – zx485
      yesterday











    • There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

      – Marc.2377
      22 hours ago












    • @Marc.2377: That's interesting, but as you said, it's an exception.

      – zx485
      4 hours ago












    • 1





      Very nicely put.

      – mjustin
      yesterday






    • 1





      To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

      – llogan
      yesterday











    • @llogan: Thank you for your clarification, it is surely helpful.

      – zx485
      yesterday











    • There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

      – Marc.2377
      22 hours ago












    • @Marc.2377: That's interesting, but as you said, it's an exception.

      – zx485
      4 hours ago







    1




    1





    Very nicely put.

    – mjustin
    yesterday





    Very nicely put.

    – mjustin
    yesterday




    1




    1





    To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

    – llogan
    yesterday





    To nitpick, you are mixing up some codecs (an encoder/decoder) and formats (what a codec outputs, or more specifically what an encoder outputs). To add to the confusion sometimes they can share the same name, and people use the term "codec" loosely. JPEG and MP3 are formats. LAME is an encoder that outputs MP3. FLAC is a format, but ffmpeg has a FLAC encoder/decoder (codec) named flac. x264 is an encoder that produces the H.264 video format (and to top it off x264 can output both lossy and lossless H.264).

    – llogan
    yesterday













    @llogan: Thank you for your clarification, it is surely helpful.

    – zx485
    yesterday





    @llogan: Thank you for your clarification, it is surely helpful.

    – zx485
    yesterday













    There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

    – Marc.2377
    22 hours ago






    There is an interesting note to be made: h.264 does have a true lossless encoding setting[2][3]. It is of course not very common to see it in use in the real world, though, as it doesn't make much sense for the vast majority of applications.

    – Marc.2377
    22 hours ago














    @Marc.2377: That's interesting, but as you said, it's an exception.

    – zx485
    4 hours ago





    @Marc.2377: That's interesting, but as you said, it's an exception.

    – zx485
    4 hours ago











    4















    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    No. You're misinterpreting that sentence.



    You can't display compressed image, just as you can't read compressed text or read file compressed with ZIP without unpacking it first. To display any image, you have to somehow represent it uncompressed in memory, pixel-for-pixel.



    This doesn't imply that the uncompressed image will be identical to original - this depends on codecs used. As far as I know there are no commonly used lossless codecs. Lossy codecs aim to represent original closely enough to make the uncompressed video indistinguishable under normal circumstances, ie. when played at predicted resolution and framerate. When looking at compressed stills (ie. framerate=0) you will certainly see artifacts, unless bitrate during compression is set impractically high (ie. producing too large output files) (this answer of mine is somehow related).




    By the way, MP4 is only a file format, ie. it tells you how compressed data is stored in a file, but doesn't determine how it was compressed. MP4 can work with a variety of codecs. H.264 is probably the most popular video codec used with MP4, but don't quote me on that. Audio is usually compressed with AAC, I guess.






    share|improve this answer

























    • @Attie Now bold "original"

      – Lightness Races in Orbit
      yesterday






    • 1





      @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

      – gronostaj
      yesterday











    • Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

      – mjustin
      yesterday












    • @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

      – gronostaj
      yesterday











    • @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

      – mjustin
      yesterday















    4















    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    No. You're misinterpreting that sentence.



    You can't display compressed image, just as you can't read compressed text or read file compressed with ZIP without unpacking it first. To display any image, you have to somehow represent it uncompressed in memory, pixel-for-pixel.



    This doesn't imply that the uncompressed image will be identical to original - this depends on codecs used. As far as I know there are no commonly used lossless codecs. Lossy codecs aim to represent original closely enough to make the uncompressed video indistinguishable under normal circumstances, ie. when played at predicted resolution and framerate. When looking at compressed stills (ie. framerate=0) you will certainly see artifacts, unless bitrate during compression is set impractically high (ie. producing too large output files) (this answer of mine is somehow related).




    By the way, MP4 is only a file format, ie. it tells you how compressed data is stored in a file, but doesn't determine how it was compressed. MP4 can work with a variety of codecs. H.264 is probably the most popular video codec used with MP4, but don't quote me on that. Audio is usually compressed with AAC, I guess.






    share|improve this answer

























    • @Attie Now bold "original"

      – Lightness Races in Orbit
      yesterday






    • 1





      @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

      – gronostaj
      yesterday











    • Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

      – mjustin
      yesterday












    • @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

      – gronostaj
      yesterday











    • @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

      – mjustin
      yesterday













    4












    4








    4








    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    No. You're misinterpreting that sentence.



    You can't display compressed image, just as you can't read compressed text or read file compressed with ZIP without unpacking it first. To display any image, you have to somehow represent it uncompressed in memory, pixel-for-pixel.



    This doesn't imply that the uncompressed image will be identical to original - this depends on codecs used. As far as I know there are no commonly used lossless codecs. Lossy codecs aim to represent original closely enough to make the uncompressed video indistinguishable under normal circumstances, ie. when played at predicted resolution and framerate. When looking at compressed stills (ie. framerate=0) you will certainly see artifacts, unless bitrate during compression is set impractically high (ie. producing too large output files) (this answer of mine is somehow related).




    By the way, MP4 is only a file format, ie. it tells you how compressed data is stored in a file, but doesn't determine how it was compressed. MP4 can work with a variety of codecs. H.264 is probably the most popular video codec used with MP4, but don't quote me on that. Audio is usually compressed with AAC, I guess.






    share|improve this answer
















    Does that mean that you can always extract the original large size videos from all the compressed formats like mp4?




    No. You're misinterpreting that sentence.



    You can't display compressed image, just as you can't read compressed text or read file compressed with ZIP without unpacking it first. To display any image, you have to somehow represent it uncompressed in memory, pixel-for-pixel.



    This doesn't imply that the uncompressed image will be identical to original - this depends on codecs used. As far as I know there are no commonly used lossless codecs. Lossy codecs aim to represent original closely enough to make the uncompressed video indistinguishable under normal circumstances, ie. when played at predicted resolution and framerate. When looking at compressed stills (ie. framerate=0) you will certainly see artifacts, unless bitrate during compression is set impractically high (ie. producing too large output files) (this answer of mine is somehow related).




    By the way, MP4 is only a file format, ie. it tells you how compressed data is stored in a file, but doesn't determine how it was compressed. MP4 can work with a variety of codecs. H.264 is probably the most popular video codec used with MP4, but don't quote me on that. Audio is usually compressed with AAC, I guess.







    share|improve this answer














    share|improve this answer



    share|improve this answer








    edited yesterday

























    answered yesterday









    gronostajgronostaj

    29.2k1472108




    29.2k1472108












    • @Attie Now bold "original"

      – Lightness Races in Orbit
      yesterday






    • 1





      @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

      – gronostaj
      yesterday











    • Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

      – mjustin
      yesterday












    • @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

      – gronostaj
      yesterday











    • @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

      – mjustin
      yesterday

















    • @Attie Now bold "original"

      – Lightness Races in Orbit
      yesterday






    • 1





      @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

      – gronostaj
      yesterday











    • Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

      – mjustin
      yesterday












    • @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

      – gronostaj
      yesterday











    • @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

      – mjustin
      yesterday
















    @Attie Now bold "original"

    – Lightness Races in Orbit
    yesterday





    @Attie Now bold "original"

    – Lightness Races in Orbit
    yesterday




    1




    1





    @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

    – gronostaj
    yesterday





    @Attie I'm interpreting "original", "large size" in OP's question as "lossless"

    – gronostaj
    yesterday













    Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

    – mjustin
    yesterday






    Well, I get to understand that if the compression is lossless and is the first transcoding from the original (not concatenated), you can always decode and encode it back to the original pixel by pixel video, but not from a lossy format.

    – mjustin
    yesterday














    @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

    – gronostaj
    yesterday





    @mjustin Exactly. What they mean is that decoder produces some uncompressed frames, not necessarily identical to original.

    – gronostaj
    yesterday













    @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

    – mjustin
    yesterday





    @gronostaj But if the decoder is decoding from an uncompressed lossless format, then the result should be identical to the original ones, pixel by pixel. That's what I understood.

    – mjustin
    yesterday











    1














    This is a very common blunder.



    You can convert from a lossy format to a lossless format, but the damage is done.



    The lossless output file will show all the damage (compromised details, added artifacts) that are the reason you don't like the lossy format. You can't get that back.



    The only option is to contact the publisher and see if he still has the original lossless files, and would be willing to somehow upload them to you.



    There's no such thing as an Enhance button. warning: TVtropes






    share|improve this answer



























      1














      This is a very common blunder.



      You can convert from a lossy format to a lossless format, but the damage is done.



      The lossless output file will show all the damage (compromised details, added artifacts) that are the reason you don't like the lossy format. You can't get that back.



      The only option is to contact the publisher and see if he still has the original lossless files, and would be willing to somehow upload them to you.



      There's no such thing as an Enhance button. warning: TVtropes






      share|improve this answer

























        1












        1








        1







        This is a very common blunder.



        You can convert from a lossy format to a lossless format, but the damage is done.



        The lossless output file will show all the damage (compromised details, added artifacts) that are the reason you don't like the lossy format. You can't get that back.



        The only option is to contact the publisher and see if he still has the original lossless files, and would be willing to somehow upload them to you.



        There's no such thing as an Enhance button. warning: TVtropes






        share|improve this answer













        This is a very common blunder.



        You can convert from a lossy format to a lossless format, but the damage is done.



        The lossless output file will show all the damage (compromised details, added artifacts) that are the reason you don't like the lossy format. You can't get that back.



        The only option is to contact the publisher and see if he still has the original lossless files, and would be willing to somehow upload them to you.



        There's no such thing as an Enhance button. warning: TVtropes







        share|improve this answer












        share|improve this answer



        share|improve this answer










        answered yesterday









        HarperHarper

        45915




        45915




















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            mjustin is a new contributor. Be nice, and check out our Code of Conduct.












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