add gstreamer as audio backend

[psych0d0g]

https://github.com/arturoc/gstreamer1.0-rs

Since portaudio has some bugs on mipsel i would like to request the addition of gstreamer,

Pros: LGPL lib. X-Platform: Linux, Android, Windows, Max OS X, iOS, as well as most BSDs, commercial Unixes, Solaris, and Symbian X-Architecture: x86, ARM, MIPS, SPARC and PowerPC, on 32-bit as well as 64-bit, and little endian or big endian Complete debugging system for both core and plugin/app developers

List of applications gstreamer is used in: https://gstreamer.freedesktop.org/apps/

And now: Open for discussion :)

[plietar]

GStreamer is a powerful but pretty big dependency, both in terms of size and complexity. I'd rather avoid it if possible. Nevertheless, I've refactored the Audio Output code to use a Sink trait. This makes it easier to add new backends for different platforms. There's an initial ALSA implementation on the alsa branch. It is only used on linux, other platforms still use portaudio.

[joerg-krause]

It's good news that you add an audio backend. Gstreamer is not applicable for low-end embedded devices, but I am glad about the ALSA implementation. I'd like to give it a try.

[psych0d0g]

@joerg-krause what is a low-end embedded device by your definition? for me my VU+ Ultimo applies as one (400mhz mips dualcode sock) and all of its multimedia features are based on gstreamer, which works just fine here.

[joerg-krause]

@psych0d0g I mean something like the Carambola 2 with 16 MB Flash and 64 MB RAM.

[psych0d0g]

well now with the sink api i would vote for gstreamer as additional sink backend

[psych0d0g]

so now after some more research from my side: this is an example pipeline that works on enigma2 mipsel: gst-launch-1.0 -v -m audiotestsrc ! audioconvert ! dvbaudiosink

the issues im facing are not mipsel specific but completely enigma2 specific. I would like to have a feature switch introduced: --with-features enigma2 which enables the audio output via gstreamer on compile time.

[psych0d0g]

i pushed my work so far here: https://github.com/psych0d0g/librespot/tree/alsa the build switch is working, aswell as the inclusiong of gstreamer rust bindings. whats not working is the gstreamer audio backend itself so far. i cant figure out what needs to be returned from the gstreamer function in order to accept audio data

[psych0d0g]

so with a little help from @plietar and https://github.com/astro , there is now a basic working gstreamer branch: https://github.com/plietar/librespot/tree/gst compile with --features enigma2 for now

[plietar]

See my comment there https://github.com/plietar/librespot/issues/63#issuecomment-198417728 This will have to wait until I reorganise the audio backends