libsndfile surround support

[gavv]

Issue to track channel orders and masks of formats supported by libsndfile.

https://libsndfile.github.io/libsndfile/api.html

Columns:

• Order - in which order enabled surround channels are packed
  • static = order is predefined by spec
  • dynamic = order is stored in file in some format
  • — = unspecified or unsupported (e.g. mono-only)
• Mask - what mask of enabled channels corresponds to every channel count
  • static = there is predefined channel mask for each channel count (like in FLAC)
  • dynamic = mask is stored in file in some format (like in WAVES and AIFF)
  • — = unspecified or unsupported (e.g. mono-only)
• CHANNEL_MAP_INFO - whether sndfile can provide channel info for this format

Format	Order	Mask	Link	CHANNEL_MAP_INFO
SF_FORMAT_WAV	—	—		—
SF_FORMAT_WAVEX	static	dynamic	doc	yes
SF_FORMAT_AIFF	dynamic	dynamic	doc	yes
SF_FORMAT_AU	—	—		—
SF_FORMAT_RAW	—	—		—
SF_FORMAT_PAF	—	—		—
SF_FORMAT_SVX	—	—		—
SF_FORMAT_NIST	—	—		—
SF_FORMAT_VOC	—	—		—
SF_FORMAT_IRCAM	—	—		—
SF_FORMAT_W64	—	—		—
SF_FORMAT_MAT4	—	—		—
SF_FORMAT_MAT5	—	—		—
SF_FORMAT_PVF	—	—		—
SF_FORMAT_XI	—	—		—
SF_FORMAT_HTK	—	—		—
SF_FORMAT_SDS	—	—		—
SF_FORMAT_AVR	—	—		—
SF_FORMAT_SD2	—	—		—
SF_FORMAT_FLAC	static	static	doc	no
SF_FORMAT_CAF	dynamic	dynamic	doc	yes
SF_FORMAT_WVE	—	—		—
SF_FORMAT_OGG / OPUS	static	static	doc	no
SF_FORMAT_OGG / PCM	static	static	doc	no
SF_FORMAT_OGG / SPEEX	—	—		—
SF_FORMAT_OGG / VORBIS	static	static	doc	no
SF_FORMAT_MPC2K	—	—		—
SF_FORMAT_RF64	static	dynamic		yes
SF_FORMAT_MPEG	—	—		—

[gavv]

libsndfile has SFC_GET_CHANNEL_MAP_INFO and SFC_SET_CHANNEL_MAP_INFO, to get/set array of enabled channels, in order as they're packed.

The question is whether these commands are available for all formats.

I'll add a column for its availability to the table.

[gavv]

http://www-cs-students.stanford.edu/~franke/SoundApp/formats.html

[gavv]

http://forum.cakewalk.com/All-those-WAV-options-when-exporting-m3384702.aspx

[gavv]

I've updated the table.

Conclusions:

• Most formats don't specify channel order. For them, let's just SMPTE by default, and make it configurable in future.

• Some formats have predefined channel orders, and some dynamic (i.e. described as meta-info in audio file).

• Luckily, for all formats with dynamic order libsndfile seems to support CHANNEL_MAP_INFO. For those formats we can dynamically map file order to our order.

• For some formats with static order libsndfile does not support CHANNEL_MAP_INFO. However, for such formats we can manually implement mapping of channel count to channel mask & order according to their spec.