audio: add DSD-over-PCM pass-through - #18312
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AF_FORMAT_S_DOP carries pre-packed DoP frames: a marker byte and 16 DSD bits per channel in the 24 MSBs of 32-bit samples, at 1/16th of the DSD bit rate. Similar to IEC61937 formats, it's meant to be exclusive not touched pass-through.
Generalize the spdif PCM fallback and the output format verification to any bitstream format instead of only IEC61937 formats.
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Map FFmpeg's AV_SAMPLE_FMT_DSD to AF_FORMAT_DSD.
FFmpeg's DSD decoders convert to PCM by default, but that conversion is deprecated. Request AV_SAMPLE_FMT_DSD instead, will be converted by SWR, when needed.
FFmpeg's DSD decoders convert to PCM by default, which is deprecated and logs a warning. Pass request_sample_fmt=dsd for the DSD codecs, the same thing ad_lavc does when decoding.
Map AF_FORMAT_S_DOP to 24 bits in 32-bit PCM containers, which is how DoP is transported over WASAPI in exclusive mode. Force exclusive mode for any non-PCM format, and don't try alternative formats for DoP. set_ao_format() now also checks the requested format before touching the ao configuration, because the DoP wire format reverse-maps to a plain PCM sample format.
Add ad_dsd, a pass-through decoder converting raw DSD audio to DoP frames, enabled with --audio-spdif=dsd. DST compressed audio is losslessly decompressed to DSD first. DoP output requires an AO with support for the format (currently ao_wasapi in exclusive mode) and a DoP capable DAC. Will fallback to PCM if not supported.
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For DST playback, need https://code.ffmpeg.org/FFmpeg/FFmpeg/pulls/23939 patch. DSD doesn't need it.