[FFmpeg-user] Wrong Channel count value on mp4a sample entry

[Yuntaek Lim]

Hi Ted,

Thank you for your replying.
I want to make clear your explain.

> It is an old container format with varied history.
Do you mean "audioSampleEntry version 0"  is old container?

> Many fields in iso container file boxes are just there to maintain
compatibility, and ignored & set to default value. In this case, the
channel count could only be 1 or 2, for mono and stereo. The default
happens to be 2.
I could not find any constraints about channel count, cannot describe greater
than 2, for audioSampleEntry from iso 14496-12:2015.
However, I've found "When values greater than 2 are used, the codec
configuration should identify the channel assignment."

I've found "Set to 1 for monaural sounds, 2 for stereo sounds. Higher
numbers of channels are not supported." from quick time format
specification. ("
https://developer.apple.com/library/archive/documentation/QuickTime/QTFF/QTFFChap3/qtff3.html#//apple_ref/doc/uid/TP40000939-CH205-75770
")

It may seem that 'mp4'  can show channel count as 6, but 'mov' cannot be
described 6 channel count in the container. If it is right, I think,
"ffmpeg" describes channel_count in AudioSampleEntry as 6 for 5.1 channel.
Do you think my thought is right wrong?


2019년 2월 13일 (수) 오후 7:53에 Ted Park <kumowoon1025 at gmail.com>님이 작성:

> > On Feb 12, 2019, at 12:49 AM, Yuntaek Lim <yuntaek.lim at gmail.com> wrote:
> >
> > I've created 5.1 channel aac-lc audio from  5.1 channel  ac-3 audio.
> > However, the sample entry of "mp4a" box show channel_count as "2", not
> "6".
> > Howerver, the  MPEG-4 elementary stream descriptor in "esds" box
> describes
> > channel count as 6.
>
> It is an old container format with varied history. Many fields in iso
> container file boxes are just there to maintain compatibility, and ignored
> & set to default value. In this case, the channel count could only be 1 or
> 2, for mono and stereo. The default happens to be 2.
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