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• ffmpeg : Video duration confused for some players on Android

  2 juin 2021, par Radi Cho

  I am using ffmpeg to scale down and compress videos to be used in Android app.
The original files are played with no problem and have no metadata issues. When I re-encode them however, the Android player is able to play them, but displays wrong durations. My app is in production and it is using official player implementations, so I wonder if there is a way to fix the corruption using ffmpeg or adding some metadata to the generated files. Hopefully that's possible, but if not - any other possible fixes will be highly appreciated :)

  


  My ffmpeg command is complex, including scaling and encoding but I can confirm this issue is reproducible on my end with the simplest ffmpeg -i video.mp4 -c:v libx264 videogen.mp4 command.

  


  I'm leaving links to the two files if that's helpful for reference.

  


  

  • video.mp4

  


  • videogen.mp4

  


  


  Any ideas what could be causing this and how to fix it ?

  


  Player issues showcase :

  
video.mp4 (original)


  

  
videogen.mp4 (re-encoded)


  

  


• ffmpeg poor YUV to RGB in sws_scale() (was : ffmpeg blocky chroma decoding)

  12 septembre 2017, par noiseshaper

  I’m using ffmpeg-3.2.4-win32, static and dev versions from zeranoe page, to decode some h264 mp4 videos I have created with x264 encoder. The videos have lots of static zones, 2d videogame type.

  When I decode their frames using either ffmpeg.exe or avcodec_decode_video2() API function, I get poor chroma resolution, blocky and quite visible in the static zones of the video (edit : avcodec_decode_video2() returns correct YUV, the problem is the YUV->RGB conversion, see my own answer below).

  With ffmpeg.exe I get poor chroma only if I output the frames to png, but if I output them to jpg, chroma seems much better (edit : this is due to poor YUV to RGB conversion of ffmpeg’s sws_scale()).

  Here is an example of the same frame obtained from a mp4 video created with a static image, the output frame is zoomed in to clearly see the effect.

  https://drive.google.com/file/d/0B5KI1D-N1kHpV3lGaERJRjNkcms/view

  1 : Original frame before compressing.

  2 : YUV 4:2:0 conversion before compressing

  3 : Video output from MPC HC + LAV decoder. This is YUV decoded output.

  4 : Video frames decoded with ffmpeg.exe to jpeg, quality is mostly ok, just some jpeg macroblocking is visible.

  5 : Video frames decoded with ffmpeg.exe to png, very blocky chroma. This is RGB output, using avcodec_decode_video2() and sws_scale() conversion to RGB produces the same blocky chroma.

  ---

  The command lines for decoding the frames to jpg and png are these :

  ffmpeg -i testcase.mp4 -vframes 5 -qscale:v 2 output%03d.jpg

  ffmpeg -i testcase.mp4 -vframes 5 output%03d.png

  You can download mp4 and bat files that showcase the effect here :

  https://drive.google.com/drive/folders/0B5KI1D-N1kHpcUdGd2IyM2pXMTg

  ---

  I have tried with ffmpeg 3.2, but same thing happens.

• ffmpeg blocky chroma decoding

  12 septembre 2017, par noiseshaper

  I’m using ffmpeg-3.2.4-win32, static and dev versions from zeranoe page, to decode some h264 mp4 videos I have created with x264 encoder. The videos have lots of static zones, 2d videogame type.

  When I decode their frames using either ffmpeg.exe or avcodec_decode_video2() API function, I get poor chroma resolution, blocky and quite visible in the static zones of the video (edit : avcodec_decode_video2() returns correct YUV, the problem is the YUV->RGB conversion, see my own answer).

  Strangely, with ffmpeg.exe I get poor chroma only if I output the frames to png, but if I output them to jpg, chroma seems much better.

  The videos are 30 fps full hd videos created from static images or from Lagarith RGB captures, converted to YUV with Rec.709 colormatrix and then input to x264.exe using crf 20 and baseline profile. Using high profile makes no difference in my tests (edit : irrelevant, since the problem is in the YUV->RGB conversion).

  If I play a mp4 video with ffplay.exe or MPC HC + LAV decoder, the chroma is good, nearly equal to the uncompressed YUV 4:2:0 version.

  Here is an example of the same frame obtained from a mp4 video created with a static image, the output frame is zoomed in to clearly see the effect.

  https://drive.google.com/file/d/0B5KI1D-N1kHpV3lGaERJRjNkcms/view

  1 : Original frame before compressing.

  2 : YUV 4:2:0 conversion before compressing

  3 : Video output from MPC HC + LAV decoder. ffplay output looks the same.

  4 : Video frames decoded with ffmpeg.exe to jpeg, some jpeg macroblocking is visible.

  5 : Video frames decoded with ffmpeg.exe to png, very blocky chroma. Using avcodec_decode_video2() function, the YUV output or its conversion to RGB produces the same blocky chroma.

  ---

  The command lines for decoding the frames to jpg and png are these :

  ffmpeg -i testcase.mp4 -vf colormatrix=bt709:bt601 -vframes 5 -qscale:v 2 output%03d.jpg

  ffmpeg -i testcase.mp4 -vf colormatrix=bt709:bt601 -vframes 5 output%03d.png

  You can download mp4 and bat files that showcase the effect here :

  https://drive.google.com/drive/folders/0B5KI1D-N1kHpcUdGd2IyM2pXMTg

  ---

  I have tried with ffmpeg 3.2, but same thing happens.