This last year I’ve become gladly impressed with two command-line pieces of software for linux: youtube-dl and mpv.

youtube-dl lets you download videos from youtube as well as from other video websites. And it does all the niceties, such as getting through playlists, parsing HTML to look for embedded videos in random webpages, and something that I appreciate a lot: it can merge several video and audio encodings (and subtitles) into the same media container. Magic.

mpv is the latest incarnation of good old mplayer (actually mplayer2). In order to play media from the console, mpv is the tool of choice.

I came across the Skammens Diskotek song a couple of weeks ago. And then I used youtube-dl to get a local copy. And then I run mpv --ao null to play just the audio, (setting the video output to the null driver). And then I noticed something strange. 100% CPU usage on my main machine (a 7th-gen quad-core Core i7).

Turns out that --vo=null disables the video output, but not the video decoding. And when youtube-dl has downloaded the full 4HD 3840x2160 video stream, just decoding the video and sending it to /dev/null takes a non-trivial amount of CPU power.

$ time mpv -vo null Sam\ \&\ Sky\ -\ Skammens\ Diskotek.webm 

real    3m8,193s
user    2m30,247s
sys     0m0,946s


The solution? Do as good nerds do, use ffmpeg to split the audio track, and then feed it to mpv via a pipe.

$ time ffmpeg -i Sam\ \&\ Sky\ -\ Skammens\ Diskotek.webm -vn -acodec copy -f opus - | mpv -

real    3m8,207s
user    0m8,134s
sys     0m1,002s

Oh yeah, that looks much better.

However, the ffmpeg+mpv approach has one disadvantage: the keyboard input is fed to ffmpeg, not to mpv. That means that I cannot, for example, seek the stream.

I thought about using FIFOs, this way I could get stdin into mpv while keeping a pipe from ffmpeg. But then there’s the problem of creating and destroying the FIFO.

And then, I noticed something in the mpv manual:

Usually, it’s better to disable video with --no-video instead.

Damn. mpv had an option to skip the decoding of the video stream, and I missed it altogether. Let’s see:

$ time mpv --no-video Sam\ \&\ Sky\ -\ Skammens\ Diskotek.webm 

real    3m8,117s
user    0m6,964s
sys     0m1,047s

Yup. And even a slightly better time than before.

ProTip™: always check the manual.