Fix the order of audio tracks in the menu

[qnga]

Fix #129 by using track infos from Playbin rather than from Discoverer.
By the way, implement VLC-like track names in the menu.

[otsaloma]

Nice! I added the review above on some specific issues and also I have a couple questions:

• Can you post a screenshot of how it looks? I'm not familiar with "VLC-like".
• Why is the language name gotten from both "get-audio-tags" and GstTag.tag_get_language_name? Is the former often missing?
• Have you checked what happens, how it looks, if the language is unspecified in the container metadata, e.g. "und" in Matroska?
• Have you checked this all works with the current Gst version requirement (>= 1.6)?

[qnga]

Thanks for the suggestions.

Can you post a screenshot of how it looks? I'm not familiar with "VLC-like".

Track titles are very useful when there are several audio tracks for the same language. For example, with a different bitrate or number of channels. When no title is available, VLC fallbacks to Track {:d}.

Why is the language name gotten from both "get-audio-tags" and GstTag.tag_get_language_name? Is the former often missing?

get-audio-tags returns a set of tags which include title, language-code and language-name. According to gstreamer documentation, the last one should be used only when no language code is available.
GstTag.tag_get_language_name returns a localized language name from a language code (see the screenshot above).

Have you checked what happens, how it looks, if the language is unspecified in the container metadata, e.g. "und" in Matroska?

Yes, everything's ok. On the screenshot below, the first track has 'mis' language code and the second one 'und'.

Have you checked this all works with the current Gst version requirement (>= 1.6)?

I tested my fix with Gstreamer 1.16.

[otsaloma]

I tested my fix with Gstreamer 1.16.

I looked at the GStreamer documentation, but unlike e.g. GTK, it doesn't seem to list what version symbols are available since. Nor can I find the documentation for 1.6 online. Usually I like to keep track of the version requirements, but never mind, maybe it's fine.

Thanks for the work, I'll merge.