[FFmpeg-user] Off topic - but still raises a Question about video formats

[Moritz Barsnick]

On Wed, Oct 14, 2015 at 20:33:13 -0600, jd1008 wrote:
> Using youtube-dl to download videos from youtube,
> I am sometimes getting this message:
> 
> WARNING: Requested formats are incompatible for merge and will be merged 
> into mkv.
> 
> Could someone please explain the reason behind this?

Well, do have a look at the video and audio codecs, e.g. with
$ ffmpeg -i resultingoutputfile.mkv

Most probably, youtube-dl defaulted to "bestvideo+bestaudio". That
could result in webm video and m4a audio. youtube-dl cannot merge webm
into mp4, therefore chooses mkv. That's all.

Actually, I think youtube-dl's warning message is confusing or wrong (I
can post a bug ticket): It says it "cannot merge", therefore it merges?
I believe it means "cannot merge to (default format) MP4, therefore
choosing MKV".

(I guess some people may expect MP4 for compatibility with their
players. People who have proper players don't mind having MKV.)

BTW, to force a "pure" MPEG video, use:
$ youtube-dl -f "bestvideo[ext=mp4]+bestaudio[ext=m4a]"
(when actually downloading from YouTube and not one of the other 5000
sites the tool supports).

That's all! Enough OT.

Moritz