On 14.05.2021 15:31, Simon Brown wrote:
[...]
For although there it says aac (LC) if I run mp4info on the resultant file
I get this:
[...]
Track 2:
flags: 3 ENABLED IN-MOVIE
id: 2
type: Audio
duration: 0 ms
language: und
media:
sample count: 0
timescale: 48000
duration: 0 (media timescale units)
duration: 0 (ms)
bitrate (computed): 125.373 Kbps
sample count with fragments: 848
duration with fragments: 868354
duration with fragments: 18091 (ms)
Sample Description 0
Coding: mp4a (MPEG-4 Audio)
Stream Type: Audio
Object Type: MPEG-4 Audio
Max Bitrate: 128250
Avg Bitrate: 0
Buffer Size: 0
Codecs String: mp4a.40.0
MPEG-4 Audio Object Type: 0 (UNKNOWN)
Sample Rate: 48000
Sample Size: 16
Channels: 2
whereas if I used -c:a aac -profile:a aac_low instead of -c:a copy then I
get this from mp4info:
Track 2:
flags: 3 ENABLED IN-MOVIE
id: 2
type: Audio
duration: 0 ms
language: und
media:
sample count: 0
timescale: 48000
duration: 0 (media timescale units)
duration: 0 (ms)
bitrate (computed): 49.589 Kbps
sample count with fragments: 849
duration with fragments: 869378
duration with fragments: 18112 (ms)
Sample Description 0
Coding: mp4a (MPEG-4 Audio)
Stream Type: Audio
Object Type: MPEG-4 Audio
Max Bitrate: 128000
Avg Bitrate: 0
Buffer Size: 0
Codecs String: mp4a.40.2
MPEG-4 Audio Object Type: 2 (AAC Low Complexity)
MPEG-4 Audio Decoder Config:
Sampling Frequency: 48000
Channels: 2
Extension:
Object Type: Spectral Band Replication
SBR Present: no
PS Present: no
Sampling Frequency: 0
Sample Rate: 48000
Sample Size: 16
Channels: 2
where it clearly states it as Mpeg-4 Audio AAC Low complexity.
Looks like the data that should be found in the "esds" atom is missing
or incomplete when using -c:a copy. See this link for details on how AAC
profile information is stored in MP4:
https://stackoverflow.com/questions/3987850/mp4-atom-how-to-discriminate-the-audio-codec-is-it-aac-or-mp3
Don't know enough about TS (de)muxing, though, to find out where this
profile data should be parsed out from the input by FFmpeg.
Regards,
Tobias
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