Pause, Change Pids, and Play Again

[Eric Montellese]

Note that if I do not call 'flush_start()' and 'flush_stop()', the
transition works correctly -- (except that the old audio and video play for
a moment after the pause, and that the decoder gets confused by the
discontinuity when the pid changes -- so the flush is definitely necessary,
I just need to know how to do it in a way that makes gstreamer happy).

Your help is appreciated.  Thanks!


On Wed, Dec 19, 2012 at 2:40 PM, Eric Montellese <
eric.montellese at videon-central.com> wrote:

> Hi folks,
>
> While playing a MPTS stream, I'm trying to pause, swap pids, and start
> playing again.  However, when I attempt to do this, the call to
> gst_element_set_state(pipeline, GST_STATE_PLAYING) is (usually) not being
> honored (and a subsequent call to get_state() does not return).  I believe
> that this is likely due to a prerolling issue, but I am unsure how to
> resolve it.  The source element is "filesrc," followed by "typefind," but
> the rest of the elements are custom plugins.  I said "usually" above,
> because on some occasions, playback will resume after a bit of a delay.
>
>
> Here's the order of my attempted steps (error checking hidden for simpler
> readability, and calls in-lined):
>
>
>
> gst_element_set_state(pipeline, GST_STATE_PAUSED);
> gst_element_get_state(pipeline, NULL, NULL, GST_CLOCK_TIME_NONE);
>
>
> //<begin code called within the demux element>
> //flush upstream and downstream.  (I have also tried only flushing
> down-stream as well, with no change in behavior)
> GST_OBJECT_LOCK(demux);
> gst_pad_push_event (GST_PAD(demux->sink_pad), gst_event_new_flush_start
> ());
> gst_pad_push_event (GST_PAD(demux->aud_src_pad), gst_event_new_flush_start
> ());
> gst_pad_push_event (GST_PAD(demux->vid_src_pad), gst_event_new_flush_start
> ());
> GST_OBJECT_UNLOCK(demux);
>
> //internally, this modifies the demux filters  (the audio and video codecs
> are the same)
> reconfigure_filter(demux, demux->filter[FILTER_AUDIO], 0x17dd);
> reconfigure_filter(demux, demux->filter[FILTER_VIDEO], 0x17dc);
>
> GST_OBJECT_LOCK(demux);
> gst_pad_push_event (GST_PAD(demux->sink_pad), gst_event_new_flush_stop ());
> gst_pad_push_event (GST_PAD(demux->aud_src_pad), gst_event_new_flush_stop
> ());
> gst_pad_push_event (GST_PAD(demux->vid_src_pad), gst_event_new_flush_stop
> ());
> GST_OBJECT_UNLOCK(demux);
>
> //internally, this sets the pcr pid
> demux_ts_set_pcr_pid(demux, 0x17dc));
>
> //internally, set the demux into the playing state
> demux_set_state(smd_element->dev_handle, ISMD_DEV_STATE_PLAY))
>
> //</end code called within the demux element>
>
>
> gst_element_set_state(pipeline, GST_STATE_PLAYING);
> gst_element_get_state(pipeline, NULL, NULL, GST_CLOCK_TIME_NONE);
>
>
>
>
>
> As I mentioned, that "get_state()" call never returns and I never see the
> GST_STATE_PLAYING event in ANY of the custom elements (all of the elements
> are custom except for 'filesrc' and 'typefind')
>
>
> For reference, the pipeline looks like this:
>
> filesrc->typefind->demux->|->vdec->vproc->vsink
>                           |->asink (an audio decoder and sink element)
>
>
>
> So what's going on?  This does not appear to be a problem with the
> internals of the custom elements, but rather an issue with not making the
> gstreamer framework happy.
>
> If I turn on lots and lots of debug prints, I will sometimes see an INFO
> print from the filesrc element saying "wrong-state" , but I also do not see
> this print reliably.
>
>  here's the print:
> 0:00:00.906761967  2292  0x8187428 INFO                 basesrc
> gstbasesrc.c:2519:gst_base_src_loop:<source> pausing after gst_pad_push() =
> wrong-state
>
> I have also tried adding a 2-second delay between each of the above calls,
> to try and narrow down any race conditions, and that *reliably* makes it
> not play.  Which is good that it's reliable, but I haven't been able to
> figure out yet why it isn't working.
>
>
> Ideas on where to investigate are appreciated, as well as general advice
> regarding flushing the pipeline from within a pipeline element.
>
> Thanks,
> Eric
>
>
>
>
>
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