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module-rtp-recv: Average the estimated real sample rate

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Maarten Bosmans 2011-01-16 01:27:29 +01:00 • committed by Colin Guthrie
parent 46200391f3
commit 2bfc0322c9
1 changed files with 22 additions and 4 deletions
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26
src/modules/rtp/module-rtp-recv.c
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@ -110,6 +110,8 @@ struct session {
pa_usec_t last_rate_update;
pa_usec_t last_latency;
double estimated_rate;
double avg_estimated_rate;
};
struct userdata {
@ -291,7 +293,7 @@ static int rtpoll_work_cb(pa_rtpoll_item *i) {
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;
double estimated_rate, alpha = 0.02;
pa_log_debug("Updating sample rate");
@ -334,11 +336,25 @@ static int rtpoll_work_cb(pa_rtpoll_item *i) {
* 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.
* In the code below a = 7 is used.
*
* Equation (1) is not directly used in (2), but instead an exponentially weighted average
* of the estimated rate R̂ is used. This average R̅ is defined as
* R̅ⁿ = α R̂ⁿ + (1-α) R̅ⁿ⁻ⁱ .
* Because it is difficult to find a fixed value for the coefficient α such that the
* averaging is without significant lag but oscillations are filtered out, a heuristic is
* used. When the successive estimates R̂ⁿ do not change much then α→1, but when there is a
* sudden spike in the estimated rate α→0, such that the deviation is given little weight.
*/
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);
if (fabs(s->estimated_rate - s->avg_estimated_rate) > 1) {
double ratio = (estimated_rate + s->estimated_rate - 2*s->avg_estimated_rate) / (s->estimated_rate - s->avg_estimated_rate);
alpha = PA_CLAMP(2 * (ratio + fabs(ratio)) / (4 + ratio*ratio), 0.02, 0.8);
}
s->avg_estimated_rate = alpha * estimated_rate + (1-alpha) * s->avg_estimated_rate;
s->estimated_rate = estimated_rate;
pa_log_debug("Estimated target rate: %.0f Hz, using average of %.0f Hz (α=%.3f)", estimated_rate, s->avg_estimated_rate, alpha);
new_rate = (uint32_t) ((double) (RATE_UPDATE_INTERVAL + latency/4 - s->intended_latency/4) / (double) RATE_UPDATE_INTERVAL * s->avg_estimated_rate);
s->last_latency = latency;
if (new_rate < (uint32_t) (base_rate*0.8) || new_rate > (uint32_t) (base_rate*1.25)) {
@ -502,6 +518,8 @@ static struct session *session_new(struct userdata *u, const pa_sdp_info *sdp_in
TRUE);
s->last_rate_update = pa_timeval_load(&now);
s->last_latency = LATENCY_USEC;
s->estimated_rate = (double) sink->sample_spec.rate;
s->avg_estimated_rate = (double) sink->sample_spec.rate;
pa_atomic_store(&s->timestamp, (int) now.tv_sec);
if ((fd = mcast_socket((const struct sockaddr*) &sdp_info->sa, sdp_info->salen)) < 0)