[FFmpeg-trac] #10158(avcodec:new): bsf 264_metadata removes stuffing bytes from NAL units - destroys original bitrate

[FFmpeg]

#10158: bsf 264_metadata removes stuffing bytes from NAL units - destroys original
bitrate
-------------------------------------+-------------------------------------
             Reporter:  emcodem      |                     Type:
                                     |  enhancement
               Status:  new          |                 Priority:  normal
            Component:  avcodec      |                  Version:  git-
             Keywords:  bsf          |  master
  264_metadata H264 filtering        |               Blocked By:
             Blocking:               |  Reproduced by developer:  0
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------
 Summary of the bug:
 When using the h264_metadata bsf, "trailing zero bytes" of all NAL's are
 removed. This leads to the output having a different bitrate than the
 input.
 This seems to be by design so i guess we talk about feature request not a
 bug. I tried to check and workaround in a custom branch but had no luck,
 it is just too complex. From feeling it starts in
 cbs_h2645_fragment_add_nals (cbs_
 h2645.c) but when i just comment the section "Remove trailing zeroes",
 output is garbage.

 How to reproduce:
 {{{
 % ffmpeg -i INPUT.h264 -codec copy -bsf:v
 h264_metadata=colour_primaries=9,h264_metadata=delete_filler=0 OUTPUT.h264
 }}}

 I created a simplified source stream for testing that only contains a
 single h264 frame in raw format, for playing with this it does not matter
 if we have one or multiple source frames or a container or elementary
 stream.
 The example source file has 2 NAL's with "trailing_zero_bytes":

 PPS: Original length 9472 bytes, length after bsf: 5 bytes
 Last IDR slice: Original length ~1 MB, length after bsf: ~80kB

 Just for explaination: the reason why the last IDR slice contains that
 much zeros is that the pic content is a colorbar but the output bitrate is
 constant 500Mbit/s (XAVC Class 300).
-- 
Ticket URL: <https://trac.ffmpeg.org/ticket/10158>
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