FR: snapclient as a source (output raw samples to stdout/pipe)

[zopieux]

Hello,

I've just learned about Snapcast, and this project is already running on my home server, phones & computers. This works just fine, thanks for developing this.

Here is a feature request: I need to read the audio stream, as snapclient would do, but then output the raw samples to stdout (instead of a sound card) so I can pipe it to another audio processing pipeline (say ffmpeg), with the end-goal of streaming to devices not supported by Snapcast today. One example that comes to mind is

snapserver → snapclient "raw mode" → ffmpeg/gstreamer with hls sink → <any HLS-enabled device>

As you can see, the missing element is snapclient "raw mode", a snapclient that would output S16LE samples directly to stdout so I could pipe them. Could this be added to snapclient as one of the (currently undocumented) --player? I've seen file_player.cpp but couldn't get it to output samples that ffmpeg could read (distorted audio).

[badaix]

It should work to write the buffer_.data() to stdout (this is undocumented, because it's not finished, PRs are welcome ;)). Maybe the distortion comes from logging (going to stdout by default). You can use a different log sink with --logsink, e.g. null or stderr.
Or you play the audio into an alsa loopback device, and record the looped audio in gstreamer (the idea is described here: https://github.com/badaix/snapcast/blob/master/doc/configuration.md#alsa)

[zopieux]

Thanks for the quick reply. I did exactly what you mentioned, aka. output data() to stdout & remove stdout clutter (I didn't bother with --logsink, I just hacked the code) and piping to ffplay -f u16le -ar 44100 -ac 2 (also tried signed & big-endian). I tried with and without calling adjustVolume. Sadly all my attempts resulted in basically noise garbage.

@badaix, I'd be happy to contribute a PR, but may I suggest you give it a try too and share the changes & format flags you used for playback, because at this point I'm not sure what to try next for this to work. Thanks for your help.

[badaix]

I've added this line fwrite(buffer_.data(), 1, needed, stdout); to master dcd8ddb
When I pipe the output to aplay, I can hear cristal clear audio:

snapclient -h 192.168.0.3 --logsink null --player file |aplay -f dat

[zopieux]

Amazing thanks! Not sure what I did wrong, but ffplay -f s16le -ac 2 -ar 44100 - works flawlessly now. I guess --player file covers my FR for now. This could use some documentation though.

[daniel-j]

I just tried it and I get bad stdout data from snapclient, compared to using a file or fifo. Snapclient prints PCM device "default" not found before the actual PCM data.
This line is the issue:

snapcast/client/snapclient.cpp

Line 388 in 7eff45f

cout << "PCM device \"" << pcm_device << "\" not found\n";

Tested with snapclient --logsink stderr --player file > file.raw
I tried using -s null but still got the extra output.
A quick workaround I found was to pipe it through tail -n +2, which skips the first line of output.

[badaix]

Fixed with commit c88b2d1

[zopieux]

Thanks, that cout gone lgtm. For your information @daniel-j.