Format mapping option

[pepie34]

It will be great to have a format mapping option for the (alsa) output plugin.

I have a external DAC linked to my computer by a toslink optical link.
By the toslink input, it can play up to 192000:24:2 and dsd64:2=dop
I'm using dop option to yes and allowed_formats with multiple PCM format and dsd64:2=dop.
Nevertheless, dsd>64 are converted to 44100:24:2 and I found no way to indicate to mpd to resample it to 176400:24:2 without enabling resampling for all other formats, loosing bitperfect and even looosing dsd64:2=dop...
I'm targeting:

• bit perfect when possible (or just 16->24bits conversion) + dsd64:2=dop + other dsd decoded to PCM 176.4, or,
• resampling with conservation of the base frequency (i.e. 44.1, 88.2 to 176.4 and 48, 96 to 192) + dsd64:2=dop + other dsd decoded to PCM 176.4

That is why, it will be great to have a finegrain mapping option.

It could be something like format_map format_pattern output_format multiple time with a priority order
An example targeting bit perfect when possible:

# DSD section
format_map "dsd64:2" "dsd64:2=dop"
## default DSD conversion
format_map "dsd*:*" "176400:24:2"
# PCM section
format_map "44100:*:*" "44100:24:2"
format_map "48000:*:*" "48000:24:2"
format_map "88200:*:*" "88200:24:2"
format_map "96000:*:*" "96000:24:2"
format_map "176400:*:*" "176400:24:2"
format_map "192000:*:*" "192000:24:2"
## default PCM conversion
format_map "*:*:*" "192000:24:2" 

Or an other example, with resampling preserving base frequency:

# DSD section
format_map "dsd64:2" "dsd64:2=dop"
## default DSD conversion
format_map "dsd*:*" "176400:24:2"
# PCM section
format_map "44100:*:*" "176400:24:2"
format_map "48000:*:*" "192000:24:2"
format_map "88200:*:*" "176400:24:2"
format_map "96000:*:*" "192000:24:2"
format_map "176400:*:*" "176400:24:2"
format_map "192000:*:*" "192000:24:2"
## default PCM conversion
format_map "*:*:*" "192000:24:2" 

This way we can tell mpd exactly what to do for different dsd formats and different PCM formats.

[pepie34]

I have looked at the filter plugin API and may be these could be implemented as a filter, not touching at all the output plugin.
Am I wrong ?