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* chmap_sel: add multichannel fallback heuristicStefano Pigozzi2014-12-291-0/+1
| | | | | | | | | | | | Instead of just failing during channel map selection, try to select a close layout that makes most sense and upmix/downmix to that instead of failing AO initialization. The heuristic is rather simple, and uses the following steps: 1) If mono is required always prefer stereo to a multichannel upmix. 2) Search for an upmix that is an exact superset of the required channel map. 3) Search for a downmix that is the exact subset of the required channel map. 4) Search for either an upmix or downmix that is the closest (minimum difference of channels) to the required channel map.
* audio: allow more than 20 channel map entrieswm42014-12-011-1/+5
| | | | | | | | | | | | | This could trigger an assertion when using ao_alsa or ao_coreaudio. The code was simply assuming the number of channel maps was bounded statically (which was true at first in both AOs). Fix by using dynamic memory allocation. It needs to be explicitly enabled by the AOs by setting a temp context, because otherwise the memory couldn't be freed. (Or at least this seems to be the most elegant solution.) Fixes #1306.
* audio: add channel map selection functionwm42013-05-121-0/+43
The point is selecting a minimal fallback. The AOs will call this through the AO API, so it will be possible to add options affecting the general channel layout selection. It provides the following mechanism to AOs: - forcing the correct channel order - downmixing to stereo if no layout is available - allow 5.1 <-> 5.1(side) fallback - handling "unknown" channel layouts This is quite weak and lots of code/complexity for little gain. All AOs already made sure the channel order was correct, and the fallback is of little value, and could perhaps be done in the frontend instead, like stereo downmixing with --channels=2 is handled. But I'm not really sure how this stuff should _really_ work, and the new code will hopefully provides enough flexibility to make radical changes to channel layout negotiation easier.