VideoReceiver: Cap rtspsrc jitterbuffer with drop-on-latency#62
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The internal rtpjitterbuffer latency is a floor that only ever grows under sender/receiver clock skew and never shrinks back, so video lag accumulates monotonically. This shows up on some newer air unit firmware revisions (different RTC behaviour) but not others, despite the same QGC pipeline. The sink is already sync=FALSE, so the accumulation is not at the sink but inside rtspsrc's jitterbuffer. Set drop-on-latency=TRUE to cap it at latency (25ms) and drop rather than grow.
The decode-path queue (tee -> queue -> valve -> decoder) ran at GstQueue defaults: non-leaky and up to 1s deep. If the decoder stalls it would back-pressure upstream and become a second place latency can accumulate, on top of the rtspsrc jitterbuffer. Make it leak the oldest buffer on overflow (drop, don't block) and cap it at 200ms so the newest frames always win and worst-case added latency stays bounded. In steady state the queue sits near-empty, so this adds no latency; it only kicks in to drop during a stall.
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The internal rtpjitterbuffer latency is a floor that only ever grows under sender/receiver clock skew and never shrinks back, so video lag accumulates monotonically. This shows up on some newer air unit firmware revisions (different RTC behaviour) but not others, despite the same QGC pipeline.
The sink is already sync=FALSE, so the accumulation is not at the sink but inside rtspsrc's jitterbuffer. Set drop-on-latency=TRUE to cap it at latency (25ms) and drop rather than grow.