[Libav-user] Checking video files

[Gabriele Greco]

I'm trying to handle video errors in advance to avoid encoding broken
files, to do it I want to decode the whole file and report if there are
errors (ffmpeg 3.4.x).

I use the "new" ffmpeg APIs, so my loop is basically

while av_read_frame(input) > 0 {
  if (index == video) {
     avcodec_send_packet() -> check error
     avcodec_receive_frame() -> check error
  }
}

the problem is that also if there are errors, for instance in one of my
samples:

[h264 @ 0x7fe8a1804400] error while decoding MB 100 67, bytestream -5
[h264 @ 0x7fe8a1804400] concealing 69 DC, 69 AC, 69 MV errors in P frame

.. in another one...

[h264 @ 0x7fe8a1803800] error while decoding MB 110 67, bytestream -12
[h264 @ 0x7fe8a1803800] concealing 59 DC, 59 AC, 59 MV errors in P frame

... no API returns me the error (except some EGAIN in the first
receive_frame() that must be ignored)

I've tried also to set videocontext.error_concealement = 0 without
differences, I see in the video context also an undocumented
err_recognition that I do not know how to use, the headers just say:

/**
     * Error recognition; may misdetect some more or less valid parts as
errors.
     * - encoding: unused
     * - decoding: Set by user.
     */
    int err_recognition;

I tried to set it to 0xfffffffff and I got my first error in
avcodec_send_packet, but I don't know if I made the right thing! :)

I remember older version of the API had error_resilience in the context
that could be used to stop decoding if something went wrong, I can also
find traces of it in the internet, but not in ffmpeg headers:

FF_ER_CAREFUL
FF_ER_COMPLIANT
FF_ER_AGGRESSIVE
FF_ER_VERY_AGGRESSIVE

... any hints on err_recognition (if it's the right thing to set and the
correct values to use)?

-- 
*Bye,*
*Gabry*

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