Category Archives: Audio

How to listen to a YouTube playlist with mpv from the command line

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This is mostly a note pad for myself with quick instructions about how to listen to a YouTube playlist with mpv from the command line.

mpv is a great player which integrates the usage of yt-dlp. That way, it is capable of playing any of the content supported by yt-dlp.

I was looking for a way to listen to a YouTube playlist without any GUI and avoiding to waste my CPU on decoding the video part I am not interested in.

This is the quick reference command to copy and paste:

$ mpv --input-ipc-server=<custom_path_to>/socket --vo=null --ytdl-raw-options="yes-playlist=,format=best*[vcodec=none]" "<youtube_playlist_url>" &

Explanation of the parameters:

  • --vo=null: No video output.

  • --ytdl-raw-options: Comma separated list of command options that will be directly passed to yt-dlp.
    • yes-playlist=: Needs the “=” and to be empty. If provided a playlist, iterate over its elements.
    • format=best*[vcodec=none]: Select the best available format and discard the video content.
  • --input-ipc-server=<custom_path_to>/socket: Creation of a socket for direct communication with mpv. Since we don’t have a GUI, this socket will allow us to control the mpv instance. For example, if we want to move to the next item in a playlist, we will run:
$ echo playlist-next | socat - <custom_path_to>/socket

I hope this is helpful!

Note:

Don’t use --vo=null if you would like to have a GUI. Then, you could also skip creating the socket with --input-ipc-server=<custom_path_to>/socket.

In that case, you could just avoid the whole format=best*[vcodec=none] yt-dlp option by passing the --no-video flag. That will save you the video processing although I’m unsure it will avoid the network transfer of the stream so better keep passing that option.

Adding subtitles to a video

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This is mostly a note pad for myself with quick instructions about how to add subtitles streams to an existent video.

Although I’m personally more in favor of using Ogg, reality is that Matroska is the one that is getting the biggest support among the Open Source container formats and it also has a great deal of features.

Also, because of widespread adoption, in spite of not having a really formal syntax and many features, SubRip is my chosen format for subtitles.

Now, I’m the owner of a Samsung 3D SmartTV which allows external SubRip .srt files. However, it also supports Matroska files with embedded subtitles and having the subtitles in the same container than the audio and video streams have some advantages. The main one is that I would be able to play such file through UPnP, with subtitles included, meanwhile that’s not possible with some UPnP servers if the subtitles are in a different file than the video. That’s the case, for example, with BubbleUPnP for Android, which I use from a tablet.

Anyway, enough introduction.

For creating a Matroska file from an existing video and a SubRip file I would use the MKVToolNix package. In a Debian based system you can install it with the following command:

root$ apt-get install mkvtoolnix

In order to merge video and a subtitles (actually, many multiple streams), the proper command for this would be mkvmerge. Its usage is quite straight forward:

$ mkvmerge -o el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo_-_with-lang-codes.mkv el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.mp4 --language 0:spa el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.srt --default-track 0
mkvmerge v7.1.0 ('Good Love') 64bit built on Jul 28 2014 11:58:03
'el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.srt': Using the demultiplexer for the format 'SRT subtitles'.
'el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.mp4' track 0: Using the output module for the format 'AVC/h.264'.
'el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.mp4' track 1: Using the output module for the format 'AAC'.
'el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.srt' track 0: Using the output module for the format 'text subtitles'.
The file 'el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo_-_with-lang-codes.mkv' has been opened for writing.
'el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.mp4' track 0: Extracted the aspect ratio information from the MPEG-4 layer 10 (AVC) video data and set the display dimensions to 1024/576.
Progress: 100%
The cue entries (the index) are being written...
Muxing took 42 seconds.

That’s basically it. With this command we will get, from a .mp4 and a .srt file, a .mkv file with both merged together. Now, if we would be wanting to add more languages we could have done something like this:

$ mkvmerge -o el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo_-_with-lang-codes.mkv el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo.mp4 --language 0:spa el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo-es.srt --language 1:eng el_ministerio_del_tiempo_-_s01e01_-_el_ministerio_del_tiempo-en.srt --default-track 0
...

This way we would be having Spanish and English subtitles, and the former would be the default one.

For more information, just check mkvmerge’s manual.

Adding a cover tag to an audio file

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This is mostly a note pad for myself with quick instructions about how to add a “cover” tag to audio files.

I usually add covers to every individual audio file from my albums so I can nicely see them when playing the file either in my computer or mobile. Often, I just use the fantastic Ex Falso application not just to add more advanced tags to my audio files but also for downloading covers from different providers.

Whenever I cannot easily find the cover I’m looking for, I would just scan it and finally save it as a 500×500 pixels JPEG file named as cover.jpg in the same directory than the audio files.

Having this into account, let’s see how to embed the cover as a tag.

MP3 or, rather, id3 tags

For id3 tags I would use the eyeD3 tool. It can be done as easily as running:

$ eyeD3 --add-image=cover.jpg:FRONT_COVER *.mp3

OGG Vorbis

In the case of OGG Vorbis files I follow a little bit more complex steps. I’m sure I could just simplify this in a single step but, by now, I’m too lazy to spend 5 minutes improving this O:)

First, I would add the cover into an individual OGG Vorbis file using the EasyTag application. I could just save the same cover on every file but I wanted to show how to do that in batch mode from the command line.

Therefore, as I said, I just save the cover into and individual file an extract all the tags from such file using the vorbiscomment tool:

$ vorbiscomment -l .oga > comments.txt

Then, I would modify the comments.txt file so it will only contain the needed art cover tags and append them to the rest of the files:

$ vorbiscomment -a -c comments.txt .oga

Hopefully, I will update this in the future with a single command to do it in a go and will also review how to be able to just link the proper cover from the audio files. Also, I will try to explain the logic for the naming of the covers in the local directory without having to add the tag to any file so crawlers like Tracker will just do the work for us.

Enjoy!

Extract, cut, join and merge audio and video streams

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This is mostly a note pad for myself with quick instructions about how to extract, cut, join and merge audio and video streams.

In Igalia we often hold meetings with several parties attending remotely. The easy setting of such meetings usually involve a shared desktop through VNC and a SIP call in a multi user room hold in our Asterisk installation.

When some of my Igalian mates cannot attend we may want to record the meeting so they can play it later. Fortunately, GNOME Shell provides integrated desktop recording out of the box and we have Asterisk set to record automatically our calls in specific multi user rooms.

So, all what it is left after a meeting is just to get both files, edit them slightly and sync them to merge them in a single multimedia container.

Usually, I would use Kdenlive in my video editing tasks. However, Kdenlive doesn’t support “video edition” without re-encoding and I would really like not to re-encode the whole stuff. Specially, the video stream. Therefore, I still will use Kdenlive for the task of syncing both streams and looking for the cutting points for both, the video and the audio file.

For most of this “without re-encoding” actions I will use the great avconv tool.

First, I will cut the video in the time 00:07:45 as starting point and 02:05:20 as ending point:

$ avconv -i screencast.webm -c:v copy -ss 00:07:45 -t 02:05:20 cut-screencast.mkv

This command basically demuxes the WebM container and extract the video stream between those two points to mux it again into a Matroska container.

Then, I will cut the audio in the starting point 00:02:13 and ending point 01:59:48. For editing OGG files we can use Oggscissors or OGG Video Tools’ oggCut .

You won’t find Oggscissors in Debian (the distribution I use). Therefore, you will have to download it and install pyvorbis and pyogg and, maybe, modify slightly the script to use the proper python interpreter. You can install the missing packages like this:

root$ apt-get install python-pyvorbis

Once with Oggscissors working, we can get the interesting audio chunk like:

$ oggscissors.py --from=133 --upto=7188 conf-call.ogg cut-confcall.ogg

or, with oggCut, like:

$ oggCut -s 133000 -e 7188000 conf-call.ogg cut-conf-call.ogg

It may happen that we actually want to extract the audio from another video file. This has happened to us, eventually, when wanting to use the audio from a synced file into another video with higher quality.

We will also use avconv for this:

$ avconv -i synced-video.ogv -map 0:1 -c:a copy synced-audio-output.ogg

It may also happen that we want to join a couple of OGG files since our SIP conf-calls sometimes have hiccups. With Oggscissors this will be done as follows:

$ oggscissors.py --join first.ogg second.ogg joint-output.ogg

With oggCat this will be done like:

$ oggCat joint-output.ogg first.ogg second.ogg

Finally, we will merge or mux the resulting video and audio files into a single media container. Again, with avconv this will be done like:

$ avconv -i final-screencast-conf-call.mkv -i cut-conf-call.ogg -c copy cut-screencast.mkv

Following the examples above this will result in a Matroska video file which contains a VP8 video stream and a Vorbis audio stream.

Hope you find this useful!