[Bug 541566] Sound glitches when pausing and resuming playback

[GStreamer (bugzilla.gnome.org)]

https://bugzilla.gnome.org/show_bug.cgi?id=541566
  GStreamer | gst-plugins-base | 0.10.x

--- Comment #3 from Hideki EIRAKU <hdk at igel.co.jp> 2012-06-26 07:21:52 UTC ---
Created an attachment (id=217264)
 View: https://bugzilla.gnome.org/attachment.cgi?id=217264
 Review: https://bugzilla.gnome.org/review?bug=541566&attachment=217264

fix for "delay between capturing the clock and pausing the audio playback" 

This bug is not fixed yet when using alsasink.  I found two issues
about the sound glitches when resuming playback.


The first issue is the same as Robert Swain mentioned above.  The
glitch is generated when gst_ring_buffer_advance() function which
increments the clock is called after capturing the clock.  This can be
monitored by looking base_time changes with GST_DEBUG=pipeline:4.

To reproduce the first issue easily, insert a short sleep as shown
below before calling gst_ring_buffer_advance() in
audioringbuffer_thread_func() function.

  if (g_atomic_int_get (&buf->state) != GST_RING_BUFFER_STATE_STARTED)
    usleep (10000);

The attached patch is my proposal for this issue.  The patch makes
gstaudiosink wait for gst_ring_buffer_advance() when pausing.


The second issue is buffer underrun of a gst ring buffer.  When
resuming/starting playback, especially on singleprocessor/singlecore
systems, the gst ring buffer may temporarily be empty that caused by:
  - The gst ring buffer is exactly the same size of the ALSA buffer.
  - The ALSA buffer is empty when resuming/starting playback.
  - Transferring data in the gst ring buffer to the ALSA buffer while
    the ALSA buffer is not filled up is done in an instant.
  - A thread running audioringbuffer_thread_func() function usually
    continues running without switching to other threads on
    singleprocessor/singlecore systems until the ALSA buffer is filled
    up.
The glitch appears if the ALSA driver starts transferring the next
data from the empty gst ring buffer (buffer underrun).

To reproduce that the gst ring buffer is temporarily empty, run a
command below on a terminal (using sh, ksh, bash or zsh), then play
the audio file on the totem, then pause and resume:

  GST_DEBUG=ringbuffer:4,alsa:4 taskset 1 totem testfile.wav 2>logfile

Then look at the logfile.  Before pausing:

0:00:02.800878995  7946  0x9cd55b8 DEBUG             ringbuffer
gstringbuffer.c:1677:default_commit: pointer at 78, write to 86-0, diff 8,
segtotal 8, segsize 3760, base 0

"diff 8, segtotal 8" means that the gst ring buffer is filled.  After
resuming:

0:00:02.801257003  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.801374580  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.801491344  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.801604551  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.801719800  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.801833163  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.802750115  7946  0x9cd5b88 DEBUG                   alsa
gstalsasink.c:857:gst_alsasink_write:<autoaudiosink1-actual-sink-alsa> written
940 frames out of 940
0:00:02.802784232  7946  0x9cd55b8 DEBUG             ringbuffer
gstringbuffer.c:1677:default_commit: pointer at 86, write to 86-0, diff 0,
segtotal 8, segsize 3760, base 0

gst_alsasink_write transfers data in the gst ring buffer to the ALSA
buffer.  "diff 0" means that the gst ring buffer is empty.

In my opinion, the second issue should be fixed by transferring data
to the ALSA buffer directly without the gst ring buffer, or using ALSA
mmap functions to share the gst ring buffer and the ALSA buffer.

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