Request - Please consider using m4a suffix for downloaded "--extract-audio" aac files.

[bat999]

Hi
I've been using the "--extract-audio" feature.
It seems to do a good job. It extracts the audio without transcoding. That's fine.

When I run command:-
youtube-dl -F http://www.youtube.com/watch?v=RdopMqrftXs
It tells me:-

Available formats:
34 : flv [360x640]
18 : mp4 [360x640]
43 : webm [360x640]
5 : flv [240x400]

When I use command:-
youtube-dl -t -f 5 --extract-audio http://www.youtube.com/watch?v=RdopMqrftXs
It downloads file:- The_Beatles_-_Let_It_Be-RdopMqrftXs.mp3

When I use command:-
youtube-dl -t -f 43 --extract-audio http://www.youtube.com/watch?v=RdopMqrftXs
It downloads file:- The_Beatles_-_Let_It_Be-RdopMqrftXs.ogg

These are both OK.

But when I use command:-
youtube-dl -t -f 18 --extract-audio http://www.youtube.com/watch?v=RdopMqrftXs
It downloads file:- The_Beatles_-_Let_It_Be-RdopMqrftXs.aac

Would it not be better if the downloaded aac file was muxed in mp4 container - so that the file suffix is m4a, not aac?
I think that FFmpeg can do this job.

If you agree that m4a is more suitable than aac, it might need to be applied to the "audio-format FORMAT" option also.
--audio-format FORMAT "best", "aac", "vorbis" or "mp3"; best by default

Thanks.

[bat999]

EDIT
I've just tried muxing the TheBeatles aac into m4a with FFmpeg.
It needs "-absf aac_adtstoasc".
Like this:-
ffmpeg -i filename.aac -vn -acodec copy -absf aac_adtstoasc filename.m4a

[tsoliman]

--extract-audio extracts the aac audio from the mp4 A/V file.
If you want it to remove video it should be called --remove-video ;)

[phihag]

You can now specify --audio-format m4a to get the desired behavior. I'm not sure why mp4 is preferable.

Unless there is a significant advantage of the mp4 container, I'm reluctant to adopt it as the default though.

[bat999]

Yes, this is OK.

youtube-dl -t -f 5 --extract-audio http://www.youtube.com/watch?v=RdopMqrftXs
produces mp3.

youtube-dl -t -f 43 --extract-audio http://www.youtube.com/watch?v=RdopMqrftXs
produces ogg.

youtube-dl -t -f 18 --extract-audio http://www.youtube.com/watch?v=RdopMqrftXs
produces aac.

And for aac wrapped in mp4 (MPEG-4 Part 14) container with m4a suffix, use the "audio-format" option.
youtube-dl -t -f 18 --extract-audio --audio-format m4a http://www.youtube.com/watch?v=RdopMqrftXs

All of them without transcoding.

m4a is suitable for iPods.

Thanks. :-)

[hickford]

Hi. (Commenting here rather than opening a new issue). Philipp, there's two advantages to saving mp4 audio in a .m4a container rather a raw .aac stream file.

1. The container allows tagging. Most software (VLC for one) can't tag .aac files.
2. The container records length information. If you play a variable bit rate .aac in your favourite audio player, you'll see the reported duration is either wrong, or fluctuates as the song plays.

---

Workaround youtube-dl --extract-audio --audio format m4a or afterwards http://superuser.com/questions/370625/ffmpeg-command-to-convert-mp3-to-aac

[rg3]

My two cents: I recall having chosen "aac" over "m4a" as the default format back in my days because my cellphone could play aac files but not m4a ones even if the codec is AAC after all.

[hickford]

Makes sense. Today's ipod is the converse - it will play .m4a but not .aac

[phihag]

Ok, we'll switch to m4a in the next release and see if anyone objects.