From d053a25b67c5e70c83ed4dcfba1032b293d2cce9 Mon Sep 17 00:00:00 2001 From: Maarten Bosmans Date: Wed, 12 Jan 2011 07:24:58 +0100 Subject: module-rtp-recv: Use new algorithm for adjusting sample rate --- src/modules/rtp/module-rtp-recv.c | 44 ++++++++++++++++++++++++++------------- 1 file changed, 29 insertions(+), 15 deletions(-) (limited to 'src/modules/rtp') diff --git a/src/modules/rtp/module-rtp-recv.c b/src/modules/rtp/module-rtp-recv.c index 3bbeb1fc..4125d281 100644 --- a/src/modules/rtp/module-rtp-recv.c +++ b/src/modules/rtp/module-rtp-recv.c @@ -109,6 +109,7 @@ struct session { pa_usec_t sink_latency; pa_usec_t last_rate_update; + pa_usec_t last_latency; }; struct userdata { @@ -286,11 +287,11 @@ static int rtpoll_work_cb(pa_rtpoll_item *i) { pa_atomic_store(&s->timestamp, (int) now.tv_sec); if (s->last_rate_update + RATE_UPDATE_INTERVAL < pa_timeval_load(&now)) { - pa_usec_t wi, ri, render_delay, sink_delay = 0, latency, fix; - unsigned fix_samples; + pa_usec_t wi, ri, render_delay, sink_delay = 0, latency; uint32_t base_rate = s->sink_input->sink->sample_spec.rate; uint32_t current_rate = s->sink_input->sample_spec.rate; uint32_t new_rate; + double estimated_rate; pa_log_debug("Updating sample rate"); @@ -314,19 +315,31 @@ static int rtpoll_work_cb(pa_rtpoll_item *i) { pa_log_debug("Write index deviates by %0.2f ms, expected %0.2f ms", (double) latency/PA_USEC_PER_MSEC, (double) s->intended_latency/PA_USEC_PER_MSEC); - /* Calculate deviation */ - if (latency < s->intended_latency) - fix = s->intended_latency - latency; - else - fix = latency - s->intended_latency; - - /* How many samples is this per second? */ - fix_samples = (unsigned) (fix * (pa_usec_t) s->sink_input->thread_info.sample_spec.rate / (pa_usec_t) RATE_UPDATE_INTERVAL); - - if (latency < s->intended_latency) - new_rate = current_rate - fix_samples; - else - new_rate = current_rate + fix_samples; + /* The buffer is filling with some unknown rate R̂ samples/second. If the rate of reading in + * the last T seconds was Rⁿ, then the increase in buffer latency ΔLⁿ = Lⁿ - Lⁿ⁻ⁱ in that + * same period is ΔLⁿ = (TR̂ - TRⁿ) / R̂, giving the estimated target rate + * T + * R̂ = ─────────────── Rⁿ . (1) + * T - (Lⁿ - Lⁿ⁻ⁱ) + * + * Setting the sample rate to R̂ results in the latency being constant (if the estimate of R̂ + * is correct). But there is also the requirement to keep the buffer at a predefined target + * latency L̂. So instead of setting Rⁿ⁺ⁱ to R̂ immediately, the strategy will be to reduce R + * from Rⁿ⁺ⁱ to R̂ in a steps of T seconds, where Rⁿ⁺ⁱ is chosen such that in the total time + * aT the latency is reduced from Lⁿ to L̂. This strategy translates to the requirements + * ₐ R̂ - Rⁿ⁺ʲ a-j+1 j-1 + * Σ T ────────── = L̂ - Lⁿ with Rⁿ⁺ʲ = ───── Rⁿ⁺ⁱ + ───── R̂ . + * ʲ⁼ⁱ R̂ a a + * Solving for Rⁿ⁺ⁱ gives + * T - ²∕ₐ₊₁(L̂ - Lⁿ) + * Rⁿ⁺ⁱ = ───────────────── R̂ . (2) + * T + * Together Equations (1) and (2) specify the algorithm used below, where a = 7 is used. + */ + estimated_rate = (double) current_rate * (double) RATE_UPDATE_INTERVAL / (double) (RATE_UPDATE_INTERVAL + s->last_latency - latency); + pa_log_debug("Estimated target rate: %.0f Hz", estimated_rate); + new_rate = (uint32_t) ((double) (RATE_UPDATE_INTERVAL + latency/4 - s->intended_latency/4) / (double) RATE_UPDATE_INTERVAL * estimated_rate); + s->last_latency = latency; if (new_rate < (uint32_t) (base_rate*0.8) || new_rate > (uint32_t) (base_rate*1.25)) { pa_log_warn("Sample rates too different, not adjusting (%u vs. %u).", base_rate, new_rate); @@ -488,6 +501,7 @@ static struct session *session_new(struct userdata *u, const pa_sdp_info *sdp_in pa_timeval_load(&now), TRUE); s->last_rate_update = pa_timeval_load(&now); + s->last_latency = LATENCY_USEC; pa_atomic_store(&s->timestamp, (int) now.tv_sec); if ((fd = mcast_socket((const struct sockaddr*) &sdp_info->sa, sdp_info->salen)) < 0) -- cgit