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

[Ted Park]

> 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.