emberwave v0.4.0

emberwave encodes: an encoder on the CPU and on the GPU whose streams upstream's decoder reads, at upstream's PSNR or above for the same bytes. On an Apple M3 Max the GPU encodes a 4K frame in about 4 ms, the CPU in about 240 ms.

Added

• An encoder on the CPU (#14): emberwave_core::encode::Encoder turns 8-bit pictures into frames within a byte budget, and emberwave-cli encode turns a Y4M video into a PWV1 file. Upstream's decoder reads its streams; at the same bytes its PSNR is upstream's encoder's or higher. It makes the same bytes on every system.
• Writers for the formats the parsers read: BlockHeader::to_words, SequenceHeader::start_of_frame_words and stream_words, and Pwv1Header::to_bytes.
• Test vectors of the encoder in testdata/encoder/, with upstream's decode of them, and scripts/gen_encoder_vectors.sh to make them. refgen encode can write its pictures (--source) and encode a Y4M file (--input).
• An encoder on the GPU (#14): gpu::Encoder runs the CPU encoder's steps as compute shaders, the forward transform, quantisation, rate control and packing, with one upload and one read-back per frame. Its frames are the CPU encoder's, or differ in some blocks where the GPU rounds a coefficient differently, at the same PSNR; on an Apple M3 Max the committed vectors come out byte for byte, and a 4K frame takes about 4 ms. emberwave-cli encode --gpu uses it, with --backend and --software as for decoding.

Changed

• emberwave-cli's Y4M reader keeps the range, the chroma siting and the frame rate of the header, reads C420paldv as chroma on the left, and reads a file a frame at a time where that is enough.
• GpuError has a new variant, Encode, for the GPU encoder's refusals; a match over every variant needs an arm for it.
• emberwave-cli encode ends with the mean, median and 99th percentile of the time per frame instead of the mean alone.