On Mon, 2017-02-27 at 13:54 +0100, Georg Chini wrote:
> case SINK_INPUT_MESSAGE_POST:
>
> - pa_sink_input_assert_io_context(u->sink_input);
> + pa_memblockq_push_align(u->memblockq, chunk);
> +
> + /* If push has not been called yet, latency adjustments in sink_input_pop_cb()
> + * are enabled. Disable them on first push and correct the memblockq. If pop
> + * has not been called yet, wait until the pop_cb() requests the adjustment */
> + if (u->output_thread_info.pop_called && (!u->output_thread_info.push_called || u->output_thread_info.pop_adjust)) {
> + pa_usec_t time_delta;
> +
> + /* This is the source latency at the time push was called */
> + time_delta = PA_PTR_TO_UINT(data);
> + /* Add the time between push and post */
> + time_delta += pa_rtclock_now() - offset;
> + /* Add the sink latency */
> + time_delta += pa_sink_get_latency_within_thread(u->sink_input->sink);
> +
> + /* The source latency report includes the audio in the chunk,
> + * but since we already pushed the chunk to the memblockq, we need
> + * to subtract the chunk size from the source latency so that it
> + * won't be counted towards both the memblockq latency and the
> + * source latency.
> + * If the source has overrun, assume that the maximum it should have pushed is
> + * one full source latency. It may still be possible that the next push also
> + * contains too much data, then the resulting latency will be wrong. */
> + if (pa_bytes_to_usec(chunk->length, &u->sink_input->sample_spec) > u->output_thread_info.effective_source_latency)
> + time_delta = PA_CLIP_SUB(time_delta, u->output_thread_info.effective_source_latency);
> + else
> + time_delta = PA_CLIP_SUB(time_delta, pa_bytes_to_usec(chunk->length, &u->sink_input->sample_spec));
Using effective_source_latency is starting to make some sense to me,
but I think the comment is not easy to understand. Are you ok with it
if I modify the comment like this:
@@ -701,9 +701,18 @@ static int sink_input_process_msg_cb(pa_msgobject *obj, int code, void *data, in
* to subtract the chunk size from the source latency so that it
* won't be counted towards both the memblockq latency and the
* source latency.
- * If the source has overrun, assume that the maximum it should have pushed is
- * one full source latency. It may still be possible that the next push also
- * contains too much data, then the resulting latency will be wrong. */
+ *
+ * Sometimes the alsa source reports way too low latency (might
+ * be a bug in the alsa source code). This seems to happen when
+ * there's an overrun. As an attempt to detect overruns, we
+ * check if the chunk size is larger than the configured source
+ * latency. If so, we assume that the source should have pushed
+ * a chunk whose size equals the configured latency, so we
+ * modify time_delta only by that amount, which makes
+ * memblockq_adjust() drop more data than it would otherwise.
+ * This seems to work quite well, but it's possible that the
+ * next push also contains too much data, and in that case the
+ * resulting latency will be wrong. */
if (pa_bytes_to_usec(chunk->length, &u->sink_input->sample_spec) > u->output_thread_info.effective_source_latency)
time_delta = PA_CLIP_SUB(time_delta, u->output_thread_info.effective_source_latency);
else
--
Tanu
https://www.patreon.com/tanuk
