[FFmpeg-user] Preserving AAC LC status when converting to fragmented MP4

Simon Brown simon.k.brown at gmail.com
Wed May 26 16:23:48 EEST 2021

> So it seems to be a matter of TS demuxing passing along the codec
> extradata correctly.
> Regards,
> Tobias
> Thank you both for your replies.

Ok, I've cheated somewhat, and taken my (much older) ffmpeg and
editted isom.c so that rather than substituting 0x40 for AV_CODEC_ID_AAC it
now substitutes 0x67 instead.  If I look at the resulting output file with
mp4info and the output of FFmpeg itself they both show that it's MP4 AAC
LC.  However, the codec string given by mp4info is mp4a.67.  If I want to
send it to a web page it has to be AAC LC, but the typically accepted codec
string is mp4a.40.2 which is also supposed to map to AAC LC.  So now I am
wondering how I would encode that in the ESDS or similar so that a) mp4info
is happy that it's mp4a.40.2 and that the chrome video decoder is happy
with the media type (because mp4a.67 codec string although in theory
supported gives me "Unrecognised media codec: mp4a.67" in Chrome.


More information about the ffmpeg-user mailing list