Request feature of merging video and audio separately served at YouTube

From the screenshot we can know YouTube now serves video and audio separately.

I think it will be great if youtube-dl can automatically merge them.

I give three ways. Either of them can be implemented into youtube-dl:

ffmpeg -i video.webm -i audio.m4a -c copy output.mkv

mkvmerge -o output.mkv video.webm audio.m4a

MP4Box -add video.mp4 -add audio.m4a output.new.mp4 && mv output.new.mp4 output.mp4

Thank you.

BTW: The worst/best decision is not accurate now, since the ‘dash’ version is not always the worst and the ‘non-dash’ version serves only up to 720p.

[AGSPhoenix]

We already have support for this, though it’s undocumented until we work out a few problems. Just specify two format codes with a + between them. For example, -f 137+140, which will get you a 1080p MP4 file. You can also combine this with specifying multiple formats by preference; for example -f 137+140/136+140/22 would try to get 1080p DASH, then 720p DASH, and finally normal 720p.

This feature isn’t enabled by default, because it requires either ffmpeg or avconv to be available and in the $PATH to mux the video, and we need to be able to automatically detect their availability, and change what format is considered the ‘best’ if they are available. It’s certainly something that could be done, but no one has taken the time to do so.

[PacoH]

OK, it works perfectly if you don’t mix formats. I successfully downloaded both wbem-video+webm-audio and mp4-video+m4a-audio formats and they were properly muxed into webm and mp4 containers respectively. Both were 4k video quality but the webm is ~1.5x the size of the mp4 and ~1.5x the bitrate.