dailz
727893fdc2
WebRTC mode now uses tier-based conservative defaults for initial encoder
bitrate instead of the aggressive formula. BWE estimate arrives within
milliseconds of client connect and overrides this; the startup value
only affects the first IDR frame.
Before (both modes used same formula):
5 * W * H * fps / 100
1440p@30fps = 5_529_600 bps (5.5 Mbps)
1440p@60fps = 11_059_200 bps (11 Mbps)
4K@30fps = 8_294_400 bps (8.3 Mbps)
After (WebRTC uses conservative tier-based, MP4 keeps formula):
fn webrtc_startup_bitrate_bps(width, height) -> u64:
pixels <= 1_000_000 (720p): 1 Mbps
pixels <= 2_500_000 (1080p): 2 Mbps
pixels <= 4_500_000 (1440p): 4 Mbps
else (4K+): 8 Mbps
Why this is safe for WebRTC:
1. BWE_INITIAL = 5 Mbps in RtcConfig (webrtc.rs)
2. Client connect triggers BWE estimate within ~10ms
3. Encoder bitrate immediately updated via BitrateCommand::UpdateBitrate
4. First IDR frame is the only output affected by startup value
5. With #23's VBV buffer_size = bitrate/4, first IDR is bounded to ~170KB
regardless of startup bitrate
Why MP4 keeps the formula:
MP4 mode has no BWE feedback channel. The formula provides reasonable
quality for file output. Users who want specific bitrate can pass --bitrate.
Resolution tiers chosen to match common display resolutions:
720p (1280x720 = 921_600 pixels) → 1 Mbps
1080p (1920x1080 = 2_073_600 pixels) → 2 Mbps
1440p (2560x1440 = 3_686_400 pixels) → 4 Mbps
4K (3840x2160 = 8_294_400 pixels) → 8 Mbps (= --max-bitrate cap)
User-supplied --bitrate flag still takes precedence in both modes.
Tests:
- cargo build --release: 0 new warnings (19 baseline preserved)
- cargo test: 97 lib + 3 integration, 0 failed
- New webrtc_startup_bitrate_tiers_by_pixel_count test covers all 4 tiers
- SAFETY comments preserved verbatim
- 1 file changed
wl-webrtc
Wayland screen capture and encoding tool.
Prerequisites
- Rust toolchain (1.70+):
rustup default stable - FFmpeg 6.0+ dev libraries with VAAPI support:
- Arch:
pacman -S ffmpeg - Ubuntu/Debian:
apt install libavcodec-dev libavformat-dev libavutil-dev libswscale-dev libva-dev - Fedora:
dnf install ffmpeg-devel libva-devel
- Arch:
- Wayland dev libraries:
- Arch:
pacman -S wayland-protocols - Ubuntu/Debian:
apt install libwayland-dev wayland-protocols - Fedora:
dnf install wayland-devel wayland-protocols-devel
- Arch:
- DRM dev libraries:
- Arch:
pacman -S libdrm - Ubuntu/Debian:
apt install libdrm-dev - Fedora:
dnf install libdrm-devel
- Arch:
Build
cargo build --release
Run
# Basic capture to file
wl-webrtc --output output.mp4
# With custom FPS and bitrate
wl-webrtc --output output.mp4 --fps 60 --bitrate 8000000
# Specify DRM device for hardware encoding
wl-webrtc --output output.mp4 --drm-device /dev/dri/renderD128
# Verbose mode
wl-webrtc --output output.mp4 -v
CLI Arguments
| Argument | Default | Description |
|---|---|---|
-o, --output |
(required) | Output file path (e.g., output.mp4) |
--output-name |
auto | Wayland output name to capture |
--fps |
30 | Target frames per second |
--codec |
h264 | Video codec (h264 only for MVP) |
--hw-accel |
vaapi | Hardware acceleration method |
--drm-device |
auto | DRM render device path |
--bitrate |
auto | Target bitrate in bps |
--gop-size |
auto | Group of Pictures size |
-v, --verbose |
false | Enable verbose logging |
--port |
0 | WebTransport server port (unused in MVP) |