lewton_decoder as default, libvorbis_decoder as optional

[awiouy]

Switch lewton_decoder as default and libvorbis_decoder as optional after #123
Works fine here

[plietar]

cc @est31

[sashahilton00]

Are there any upsides/downsides to doing this? Presumably libvorbis is more mature?

[est31]

Upsides:

• safety. There have been multiple CVEs against libvorbis. lewton on the other hand doesn't use a single line of unsafe code.
• no need for a C compiler

Downsides:

• lewton needs to be compiled in release mode in order to have comparable speed to libvorbis. lewton still is faster than realtime in debug mode, but be prepared for startled users :).
• yes libvorbis has been around longer and has less bugs. If you find any bug in lewton, please report it!

[sashahilton00]

Thanks for clarifying. Sounds like we could make the switch to lewton as default without too much impact then. We may also want to consider switching the default build mode to release if we do make lewton the default, depending on the speed, but given that librespot is eventually to be the behind-the-scenes library for the daemon, it's probably unnecessary. Thoughts?

[plietar]

We may also want to consider switching the default build mode to release

AFAIK there isn't a way of changing what cargo build does. The best we can do is use --release in the README (which is already the case).

There's a couple of other places in librespot which are pretty slow in debug mode (generating DH keys during handshake for example takes a handful of seconds on x86_64, and likely a lot more on low end devices) so this isn't really a concern to me.

[awiouy]

I have rebased this against current #123

It now builds as follows:

• neither with-tremor nor with-vorbis: lewton
• with-tremor: tremor
• with-vorbis: vorbis
• both with-tremor and with-vorbis: tremor

In summary:

• tremor is implemented using fixed point arithmetic, which is suitable for devices without hardfloat support
• lewton and vorbis are alternatives for other devices

Chosing between lewton and vorbis:
Many pros and cons have been presented above. For me, the main advantage of lewton over vorbis, is that lewton requires far less dependencies, especially system dependencies such as gcc, ogg..sys and vorbis..sys. Moreover, lewton has a very reactive support, see above and #123.

[sashahilton00]

If no one objects, I'll merge this in a couple of hours and update the docs.