The function is quite important to ensure that the output
is always going to be sufficient, and it can change version to
version, so exposing it makes sense.
This allows the encoder to fully saturate all queues the GPU
has, giving a good 10% in certain cases and resolutions.
This also improves error resilience if an allocation fails,
and properly cleans up after itself if it does.
Unlike the software FFv1 encoder, none of our buffers are allocated by
FFmpeg, which supports at most 4GiB large allocations.
For really large sizes, the maximum size of the buffer can exceed 4GiB,
which the software encoder optimistically tries to allocate as 4GiB
in the hopes that the encoder will compress to under that amount.
We can just let Vulkan allocate us a larger buffer, and switch to
64-bit offsets.
This commit implements a standard, compliant, version 3 and version 4
FFv1 encoder, entirely in Vulkan. The encoder is written in standard
GLSL and requires a Vulkan 1.3 supporting GPU with the BDA extension.
The encoder can use any amount of slices, but nominally, should use
32x32 slices (1024 in total) to maximize parallelism.
All features are supported, as well as all pixel formats.
This includes:
- Rice
- Range coding with a custom quantization table
- PCM encoding
CRC calculation is also massively parallelized on the GPU.
Encoding of unaligned dimensions on subsampled data requires
version 4, or requires oversizing the image to 64-pixel alignment
and cropping out the padding via container flags.
Performance-wise, this makes 1080p real-time screen capture possible
at 60fps on even modest GPUs.
