How to resume playing after paused using gstreamer?

Question

I've written C++ wrapper for each Gstreamer types. They're simple and intuitive, so I don't think their implementation needs to be posted here (though I could post them (maybe at github) if need arises).

The problem I'm facing is that I start playing a video (and simulteneously saving it to a file using gst tee element)....and while it is playing, I pause (from different thread) which is working great. However, when I want to resume it, it doesn't work:

void pause()
{
    _pipeline.state(GST_STATE_PAUSED)
}

void resume()
{
    _pipeline.state(GST_STATE_PLAYING);
}

And here is the play() function where I create the pipeline and set it state to GST_STATE_PLAYING.

int play(std::string const & source_path, std::string const & save_as_file)
{
    gst::element source(source_path.substr(0,4) == "http" ? "souphttpsrc" : "filesrc", "media-source");
    gst::element demuxer("decodebin", "decoder");
    gst::element vconv("videoconvert",  "vconverter");
    gst::element vsink("autovideosink", "video-output");
    gst::element aconv("audioconvert",  "aconverter");
    gst::element asink("autoaudiosink", "audio-output");
    gst::element filesink("filesink", "file-sink");
    gst::element fq("queue", "file-queqe");
    gst::element tee("tee", "media-tee");
    gst::element aq("queue", "audio-queue");
    gst::element vq("queue", "video-queue");

    source.set("location", source_path.c_str());

    gst::bus bus = _pipeline.bus();
    guint bus_watch_id = _session.add_watch(bus);


    _pipeline.add(source, demuxer, vconv, vsink, aconv, asink, filesink, tee,fq, aq, vq);

    gst::element::link(source, tee); 

    gst::element::link(vq, vconv, vsink);
    gst::element::link(aq, aconv, asink);

    gst::pad tee_src_pad = tee.request_pad("src_%u");
    gst::pad demuxer_sink_pad = demuxer.static_pad("sink");

    gst::pad::link(tee_src_pad, demuxer_sink_pad);

    filesink.set("location",  save_as_file.c_str());

    gst::element::link(fq, filesink);

    gst::pad tee_src_pad2 = tee.request_pad("src_%u");
    gst::pad fq_pad = fq.static_pad ("sink");
    gst::pad::link(tee_src_pad2, fq_pad);

    gst::element::dynamic_link(demuxer, aq);
    gst::element::dynamic_link(demuxer, vq);

    g_print ("Now playing: %s\n", source_path.c_str());
    _pipeline.state(GST_STATE_PLAYING);

    //code
    _session.run()

    //cleanup
}

I'd appreciate if anybody could help me figuring out the solution to this problem.

I'm playing the video on Qt widget using its handle and passing it to gstreamer video overlay.

Answer 1

Do you have queue elements on each branch that comes off the tee? One for the file and one for the decode? You could also try messing around with the "sync" property on the filesink. Maybe set it to true.

---

Edited by Nawaz.

Since this answer first gave me few directions and almost a very-near-to-the-solution direction, it deserves the bounty I've set for this question. But before that, here is the solution (explanation is in my answer - Nawaz).

gst::element filesink("filesink", "file-sink");
filesink.set("async", gboolean(FALSE));

Hope that helps other as well.

Answer 2

I found the answer myself. I tried to print the status of all the elements as:

void print_status_of_all()
{
    auto it  = gst_bin_iterate_elements(GST_BIN(_pipeline.raw()));
    GValue value = G_VALUE_INIT;
    for(GstIteratorResult r = gst_iterator_next(it, &value); r != GST_ITERATOR_DONE; r = gst_iterator_next(it, &value))
    {
         if ( r == GST_ITERATOR_OK )
         {
             GstElement *e = static_cast<GstElement*>(g_value_peek_pointer(&value));
             GstState  current, pending;
             auto ret = gst_element_get_state(e, &current, &pending, 100000);
             g_print("%s(%s), status = %s, pending = %s\n", G_VALUE_TYPE_NAME(&value), gst_element_get_name(e), gst_element_state_get_name(current), gst_element_state_get_name(pending));
         }
    }
}

And then it helped me figured out that the status of all the elements were changing from PLAYING to PAUSED and PAUSED to PLAYING, without any pending state, except filesink element whose state remains at PLAYING and a pending PAUSED state (which is because it attempts to change it asynchronously) — that eventually led me to the async property of the GstBaseSink which is the base class of filesink. I just set it to FALSE as:

gst::element filesink("filesink", "file-sink");
filesink.set("async", gboolean(FALSE));

That's it. Now pause and resume works great — status of all the elements change to PLAYING to PAUSED and PAUSED to PLAYING, without any pending state!