Constant SLICES_PER_FRAME 

const SLICES_PER_FRAME: u32 = 4;

Slices per H.264 frame, the count the VA-API (SLICES; one for H.264 on AMD’s VCE) and OpenH264 (SM_FIXEDSLCNUM_SLICE) sessions emit too: a client decoding in software threads a frame across its slices, and more than four upsets some Chromium decoders. What the slices cost at a fixed quantizer is measured by gpu_bench_slices. An HEVC frame is one slice, since no decoder a client has threads HEVC’s plain slices (FFmpeg threads its wavefronts and tiles), and its band frames take theirs where a band starts (set_band_layout). AV1 partitions by tiles instead, asked for as 1x1 in configure_codec.