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• Tools/Techniques for investigating video corruption — ffmpeg / libavcodec

  17 juillet 2013, par Gopherkhan

  In my current work I'm trying to encode some images to h264 video using the FFMPEG's C library. The resulting video plays fine in VLC, but has no preview image. The video can play in VLC and Mplayer on ubuntu, but won't play on Mac or PC (in fact, it causes a "VTDecoderXPCService quit unexpectedly" error on Mac).

  If I run the resulting file through FFMPEG using the command line, the resulting file has a preview image, and plays correctly everywhere.

  Apparently the file that I get out of the program is corrupt in some weird place, but I don't have any output during my compilation or run to indicate where. I can't share my code at the moment (work code isn't open source yet :-( ), but I have tried a number of things :

  1. Writing only header and trailer data (av_write_trailer) and no frames
  2. writing frames only minus the trailer (using avcodec_encode_video2 and av_write_frame)
  3. Adjusting our time_base and frame pts values to encode only one frame per second
  4. Removing all variable frame rate code
  5. Numerous other variants that I won't bother you with here

  In creating my project, I've also followed the following tutorials :

  • Dr. Anger's FFMPEG tutorial
  • FFmpeg's Own Tutorials
  • An older tutorial from FFmpeg

  And consulted the deprecated ffmpeg functions list

  And compiled FFMPEG on ubuntu according to the official doc

  And consulted numerous StackOverflow questions :

  • Raw H264 frames in mpegts container using libavcodec
  • How to encode Bitmaps into a video using MediaCodec ?
  • How to convert RGB from YUV420p for ffmpeg encoder ?
  • Encoding H.264 video using FFmpeg C API
  • ffmpeg : how to save h264 raw data as mp4 file

  But every run of the program runs into the exact same problem.

  My question is, is there anything obvious that causes a programmatic run of FFMpeg to differ from a console run (e.g., an incomplete finalization, some threading issues, etc.) ? Like some obvious reason that a console run could repair a corrupted file ? Or is there a decent tool/method for inspecting a video file and finding the point of corruption ?

• Merge commit ’b70d7a4ac72d23f3448f3b08b770fdf5f57de222’

  15 mai 2014, par Michael Niedermayer

  Merge commit ’b70d7a4ac72d23f3448f3b08b770fdf5f57de222’
  * commit ’b70d7a4ac72d23f3448f3b08b770fdf5f57de222’ :
  
    lavc : add a native Opus decoder.
  Conflicts :
  
  	Changelog
  
  	configure
  
  	libavcodec/version.h
  Fate tests pass with both avresample as well as swresample based opus decoder, but
  
  are disabled (reference files are very large so i want to think a day or 2 about
  
  if theres an alternative or if they could be avoided, they also dont match the
  
  official samples)
  Merged-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] Changelog
  • [DH] configure
  • [DH] libavcodec/Makefile
  • [DH] libavcodec/allcodecs.c
  • [DH] libavcodec/opus.c
  • [DH] libavcodec/opus.h
  • [DH] libavcodec/opus_celt.c
  • [DH] libavcodec/opus_imdct.c
  • [DH] libavcodec/opus_parser.c
  • [DH] libavcodec/opus_silk.c
  • [DH] libavcodec/opusdec.c
  • [DH] libavcodec/version.h
  • [DH] tests/Makefile
  • [DH] tests/fate/opus.mak

• Naive Sorenson Video 1 Encoder

  12 septembre 2010, par Multimedia Mike — General

  (Yes, the word is “naive” — or rather, “naïve” — not “native”. People always try to correct me when I use the word. Indeed, it should actually be written with 2 dots over the ‘i’ but who has a keyboard that can easily do that ?)

  At the most primitive level, programming a video encoder is about writing out a sequence of bits that the corresponding video decoder will understand. It’s sort of like creating a program — represented as a stream of opcodes — that will run on a given microprocessor or virtual machine. In fact, reading a video codec bitstream specification will reveal a lot of terminology along the lines of “transmitting information to the decoder” or “signaling the decoder to do xyz.”

  Creating a good encoder that will deliver decent quality at a reasonable bitrate is difficult. Creating a naive encoder that produces a technically compliant bitstream, not so much.

  
  
  

  When I wrote an FFmpeg encoder for Sorenson Video 1 (SVQ1), the first step was to just create a minimally compliant bitstream. The coarsest encoding mode that SVQ1 allows is to encode the average (mean) of each 16×16 block of samples. So I created an encoder that just encoded the mean of each block. Apple’s QuickTime Player was able to play the resulting video in all of its blocky glory. The result rather reminds me of the Super Nintendo’s mosaic effect.

  Level 5 blocks (mean-only 16×16 encoding) :
  

  
  
  

  Level 3 blocks (mean-only 8×8 encoding) :
  

  
  
  

  It’s one thing for your own decoder (in this case, FFmpeg’s own decoder) to be able to decode the data. The big test is whether the official decoder (in this case, Apple QuickTime Player) can decode the file.

  
  
  

  Now that’s a good feeling. After establishing that sort of baseline, it’s possible to adapt more and more features of the codec.