[FFmpeg-devel] [PATCH 3/5] avformat/movenc: implement writing of the btrt box

[Martin Storsjö]

On Sun, 20 Sep 2020, Jan Ekström wrote:

> This is utilized by various media ingests to figure out the bit
> rate of the content you are pushing towards it, so write it by
> default for video, audio and subtitle tracks. It is only mentioned
> for timed metadata sample descriptions in QTFF, so limit it only to
> ISOBMFF (MODE_MP4).
>
> Updates the FATE tests which have their results changed due to the
> 20 extra bytes being written per track.
> ---
> libavformat/movenc.c               |  29 ++++++++
> tests/fate/mov.mak                 |   2 +-
> tests/ref/fate/binsub-movtextenc   |   2 +-
> tests/ref/fate/copy-trac3074       |   4 +-
> tests/ref/fate/movenc              | 102 ++++++++++++++---------------
> tests/ref/lavf-fate/av1.mp4        |   4 +-
> tests/ref/lavf-fate/h264.mp4       |   4 +-
> tests/ref/lavf/mp4                 |  12 ++--
> tests/ref/vsynth/vsynth1-mpeg4     |   4 +-
> tests/ref/vsynth/vsynth2-mpeg4     |   4 +-
> tests/ref/vsynth/vsynth3-mpeg4     |   4 +-
> tests/ref/vsynth/vsynth_lena-mpeg4 |   4 +-
> 12 files changed, 102 insertions(+), 73 deletions(-)

Not familiar with the box or its use, but the change looks pretty sensible 
to me.

Are there cases where there's really no sensible information about 
bitrates to write, where it would be preferrable to just drop it, instead 
of writing a box with bogus values?

// Martin