Experimental options

Everything here is off by default. Read the limits before turning it on.

Forward error correction

FEC adds redundancy so lost packets can be rebuilt without a retransmission.

Do not enable FEC for browser clients

Chrome’s H.264 decoder needs contiguous RTP sequence numbers. FEC here shares the sequence space with media, so Chrome sees gaps and demands keyframes repeatedly. The keyframe storm is far worse than the loss it was meant to fix.

Setting	Default	Purpose
QUASAR_FEC_MODE	derived	off, fixed or auto.
QUASAR_FEC_PERCENTAGE	0	Redundancy percentage in fixed mode.

auto starts at 0%, ramps up only when it sees loss, and unwinds when the link is clean. Still not recommended for browsers. FEC also takes bitrate from the video.

Intra refresh

Replaces periodic keyframes with a rolling wave of intra-coded blocks. Loss recovery takes at most one refresh cycle and the keyframe bitrate spike goes away.

QUASAR_INTRA_REFRESH=1
QUASAR_INTRA_REFRESH_PERIOD=60

60 is the validated period; 0 means continuous.

• Vulkan encoder only (QUASAR_ENCODER=vulkan).
• Needs a patched image. On stock GStreamer it silently does nothing.
• H.264 only. HEVC and AV1 ignore it, with a warning.
• Use more than one slice: the cycle length follows the slice count.

On an impaired test link it produced no visible hitches, where refresh off stalled under loss.

Resolution and frame-rate ABR rungs

QUASAR_ABR_LADDER_RESOLUTION and QUASAR_ABR_LADDER_FPS work but default off pending broader hardware validation. They need QUASAR_ABR_MODE=smooth and apply to the next session. Limits: Adaptive bitrate.

Not knobs

• apps.default_vram_mb is deprecated and was never enforced. Live telemetry replaced it.
• The in-compositor NV12 mode was removed.
• A native client isn’t usable yet.

Before you change anything

Measure, change one thing, measure again. Differences are often smaller than run-to-run noise. See Diagnostics.