- Pre-allocate and reuse sample decompression buffers. In many FLAC
files, the amount of samples per frame is either constant or the
largest frame will be hit within the first couple of frames. Also,
during audio output, we need to move and combine the samples from the
decompression buffers into the final output buffers anyways. Avoiding
the reallocation of these large buffers provides an improvement from
16x to 18x decode speed on strongly compressed but otherwise usual
input.
- Leave a FIXME for a similar improvement that can be made in the
residual decoder.
- Pre-allocate audio chunks if frame size is known.
- Use reasonable inline capacities in several places where we know the
maximum or usual capacity needed.
We downsample multi-channel files into stereo for now, which at least
makes the other channels listenable. The new multi-channel downmix
helper is intended to be used for other formats with the same or similar
channel arrangement, such as QOA.
