Clarify unit prefix for Track.bitrate

[tkem]

According to the docs [https://docs.mopidy.com/en/develop/api/models/#mopidy.models.Track], Track.bitrate is supposed to be in kbit/s. Browsing my local media collection using the file backend, bitrates are reported in bit/s, though.

AFAICS, the bitrate property is set from the Gst.TAG_BITRATE value in https://github.com/mopidy/mopidy/blob/develop/mopidy/audio/tags.py#L109, which is given in bit/s according to https://developer.gnome.org/gstreamer/stable/gstreamer-GstTagList.html#GST-TAG-BITRATE:CAPS.

Given that it's usually easier to change the documentation than the source, and that I can't see any added value in rounding this to kbit/s, I'd suggest changing the docs to reflect existing practice. The question is if this affects any extensions, and if/how this change should be communicated.

[jodal]

Mopidy-Spotify sets track.bitrate in kbit/s, e.g. 160. Thus, this sounds like a bug in Mopidy-File.

[tkem]

AFAICS, this also affects the local backends. I was just leaning towards changing the docs, since it feels more "natural" and less error-prone for extensions to get it right (see linked issues). However, I'd be happy either way, as long as this gets clarified.

[tkem]

Any new thoughts on this? Either way is fine with me, I think we should just aim for consistency...