Four encoder quality improvements, all sender-side:
- CRF rate control (default 22, --crf to override): targets a
constant visual quality level instead of a fixed bitrate. Static
desktop content uses 300-800 kbps (vs. forced 4000+), and the saved
bits go to sharp text and clean motion when they appear. The VBV
max rate (the --bitrate value, now a cap rather than a target)
bounds bursts so the receiver's UDP buffers stay safe. Round-trip
test bitrate dropped from 1390 kb/s to 47 kb/s on synthetic frames
— the encoder uses only what it needs.
- 5-second GOP (was 1 second): 80% fewer keyframe bits freed for
detail frames. Screen content changes incrementally, not
wholesale; PLI feedback recovers from loss in one frame time
regardless of GOP length.
- faster preset (was veryfast): better sub-pixel estimation and
RDO on more decisions. The desktop handles it trivially at 1080p.
- Screen-content x264 tuning: aq-mode=2 (auto-variance AQ moves
bits away from flat areas toward text edges) and psy-rd=1.5
(preserves texture sharpness).
Combined with the earlier veryfast upgrade and sender-side
downscaling, this is roughly 2x the perceived quality at the same
average bandwidth compared to the original ultrafast ABR encoder.
meson test 5/5 in both configurations, valgrind clean.
Add FFmpeg-based encoder/decoder with SPS/PPS extradata, Annex-B output
normalization, low-latency libx264 settings, and a round-trip unit test.
Includes review hardening: cached SwsContext, bitrate-only rate control,
std::byte/uin8_t cast helpers, and richer test assertions.
fegger