Hello,
On 7/26/23 00:09, "zhilizhao(赵志立)" wrote:
On Jul 26, 2023, at 00:28, Raphaël Zumer <raphael.zu...@vimeo.com> wrote:
Encoding PCM in MP4 currently causes subsequent decoding to fail due to a
sample size of 0.
This doesn’t give a context on which case the sample size is 0.
Using FFmpeg (round-trip). Just mux some Wave file to MP4 and try decoding it
back. Unless it is sample-dependent for some reason, it will always fail.
Use bits per coded sample instead, which are set correctly based on my tests
and allow muxed files to be decoded as expected.
Since neither bits_per_raw_sample or bits_per_coded_sample has strong guarantee,
I decided to fall back to av_get_exact_bits_per_sample().
http://ffmpeg.org/pipermail/ffmpeg-devel/2023-July/312653.html
Can you show or describe a case where bits_per_raw_sample is set and not
bits_per_coded_sample?
For PCM av_get_exact_bits_per_sample() looks fine, but if the behavior of
bits_per_raw_sample/bits_per_coded_sample is inconsistent on decode that seems
undesirable or undocumented behavior that should be rectified.
Looking at the documentation
(https://ffmpeg.org/doxygen/6.0/structAVCodecParameters.html) it is mentioned
to be equivalent to bits_per_raw_sample for PCM formats. So this looks like a
bug.
Note: PCM in MP4 muxed with versions of FFmpeg 6.0 and prior (before
implementation of the pcmC box) will continue to fail decoding due to the
sample size not being available. I see that it was assumed to be 16-bit before
commit d4ee17.
The assumption is incorrect. We didn’t recognize those samples are
ISO/IEC 23003-5 before.
I mean that it is possible to mux s16 PCM into MP4 (in a nonstandard way I
guess) prior to that patch set and this breaks decoding files created this way.
I can mux a s16le Wave file using FFmpeg 6.0 to MP4, it will be decoded
correctly and retain the sample format. Try to decode it using FFmpeg post the
23003-5 patch and it simply fails decoding because there's no pcmC box.
There doesn't need to be a fallback, just a consideration.
Thanks
Raphaël Zumer
_______________________________________________
ffmpeg-devel mailing list
ffmpeg-devel@ffmpeg.org
https://ffmpeg.org/mailman/listinfo/ffmpeg-devel
To unsubscribe, visit link above, or email
ffmpeg-devel-requ...@ffmpeg.org with subject "unsubscribe".
