Closes https://github.com/MusicPlayerDaemon/MPD/issues/1297

MPD supports only 8 channels, so MAX_CHANNELS is enough, the array
doens't need to be SPA_AUDIO_MAX_CHANNELS (which is 64).

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1297

Requires PipeWire 0.3.32.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1283

This bug caused a 9 second offset in all time stamps.  Due to that,
the Snapcast server thought the chunks are too old and discarded them.

Fixes https://github.com/MusicPlayerDaemon/MPD/discussions/1287

Don't allocate any memory until the output is really enabled.

The implementation was removed 12 years ago in commit f6455d5f and
nobody missed it.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/1265

This way, we know whether we're explicitly "paused" or "not yet
activated because the ring buffer hasn't been filled yet".

emplace already calls std::pair. No need for it again.

No need to emplace when calling std::make_shared.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

make_pair is an old C++98 function that can be replaced by modern
shorter constructs.
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Signed-off-by: Rosen Penev <rosenp@gmail.com>

The ChainFilter class is extremely complicated code, and will grow to
be even more complicated when the Filter interface gets extended.
Let's just remove it; we can easily chain many TwoFilters instead.

Found with readability-use-anyofallof
Signed-off-by: Rosen Penev <rosenp@gmail.com>

Found with modernize-use-default
Signed-off-by: Rosen Penev <rosenp@gmail.com>