Re: [gentoo-user] OT: what audio file format / container to play on Android.

[Mick]

On Wednesday 06 Jul 2016 16:07:17 Stroller wrote:
> > On 5 Jul 2016, at 16:54, wabe <wabenbau@×××××.com> wrote:
> >
> > If you wanna put the audio data into another container without recoding
> > it, you can use for example something like that:
> >
> > ffmpeg -i filename.mp4 -acodec copy filename.m4a
>
> This has worked. Many thanks for your help.
>
> I did not actually expect this, as I thought .mp4 and .m4a were the same
> thing (see links below) and renaming the .mp4 to .m4a  did not have any
> effect.

They are not exactly the same thing, in the sense that m4a ought to only have 
an audio stream in it, but mp4 may have more streams (audio and video).


> ffmpeg did, however, seem to do no more than copy the stream (it took only a
> second or so), so presumably it has marked the container differently
> somehow. See attached, anyone who's interested.

If you notice youtube-dl used ffmpeg after it downloaded your file to fix 
something in the aac bitstream, which it considered 'malformated':

[download] Destination: The Bronze Age Collapse, In Our Time - BBC Radio 4-
b07fl2qw.mp4
[download] 100% of 40.56MiB in 01:36
[ffmpeg] Fixing malformated aac bitstream in "The Bronze Age Collapse, In Our 
Time - BBC Radio 4-b07fl2qw.mp4"

If you run ffprobe on the partly downloaded mp4 file before youtube-dl completes 
and has a chance to use ffmpeg, you can compare its output with the 'fixed' mp4 
file and then your own m4a audio extract to see what the differences might be.

> I appreciate the contributions of all who've replied,
>
> Stroller.
>
>
>
> [1] http://stackoverflow.com/questions/9412384/
> [2] https://en.wikipedia.org/wiki/MPEG-4_Part_14#.MP4_versus_.M4A
> [3] https://wiki.jriver.com/index.php/MP4_and_M4A_File_Support

-- 
Regards,
Mick