AW: [External] Re: Restarted stream contains legacy frames

Mon Sep 7 07:02:51 UTC 2020

Hi Nicolas,

thanks for your response.

unfortunately the states "null" and "ready" didn't solve the problem. I also tried to completely re-initialize the pipeline and faced very a strange behavior. When I unref my pipeline and do the re-init afterwards, I can see the old frames. But when I do not unref the pipeline but simply "override" my references, only the new frames are displayed (as desired).

I've attached my simplified source code below, maybe you see what's wrong. Case (1) shows the working code (even if it leaks) case (2) does not work.

void Streamer::init()
{
    auto pipeline = gst_pipeline_new( "pipeline" );
    auto src = gst_element_factory_make( "udpsrc", "source" );
    auto depay = gst_element_factory_make( "rtph264depay", "depay" );
    auto dec = gst_element_factory_make( "avdec_h264", "dec" );
    auto convert = gst_element_factory_make( "videoconvert", "convert" );
    auto upload = gst_element_factory_make( "glupload", "upload" );
    auto sink = gst_element_factory_make( "appsink", "sink" );

    gst_app_sink_set_drop( sink, true );
    gst_app_sink_set_max_buffers( sink, 1 );
    gst_app_sink_set_emit_signals( sink, true );

    GstAppSinkCallbacks callbacks = { nullptr, newPreroll, newSample, nullptr };
    gst_app_sink_set_callbacks( m_data->sink, &callbacks, this, nullptr );

    gst_bin_add_many( GST_BIN( pipeline), src, depay, dec, convert, upload, sink, NULL );

    if( !gst_element_link_many( src, depay, dec, convert, NULL ) ) { return nullptr; }

    GstCaps* caps =  gst_caps_from_string( "video/x-raw, format=BGR" );

    if( !gst_element_link_filtered( convert, upload, caps ) ) { return nullptr; }

    if( !gst_element_link( upload, sink ) { return nullptr; }

    // Do further config ...

    // Inject gl context

    m_pipeline = pipeline;

    gst_element_set_state( m_pipeline, GST_STATE_PLAYING );
}

void Streamer::restart()
{
// Working (1)
gst_element_set_state( m_pipeline, GST_STATE_NULL );
init();

// Not working (2)
gst_element_set_state( m_pipeline, GST_STATE_NULL );
gst_unref_object(m_pipeline);
init();
}

Is it sufficient to call gst_unref_object ( m_pipeline ) in order to completely free all sources, or is it necessary to unref  all elements added to the pipeline manually? I'm not completely sure about this point.

As you can see above, I'm using static names for the GstElements added to the pipeline. In the doc it says that if no name is given, a unique name is generated. Is the name used internally for any referencing or sth like that?

I really thought, that if I create a new pipeline no frames will be buffered at all.

Thanks in advance
Michael

-----Ursprüngliche Nachricht-----
Von: gstreamer-devel [mailto:gstreamer-devel-bounces at lists.freedesktop.org] Im Auftrag von Nicolas Dufresne
Gesendet: Freitag, 4. September 2020 23:42
An: Discussion of the development of and with GStreamer <gstreamer-devel at lists.freedesktop.org>
Betreff: [External] Re: Restarted stream contains legacy frames

Le vendredi 04 septembre 2020 à 10:18 +0000, Timtchenko, Michael a écrit :
> Hi gstreamers,
>
> i’m facing a little problem regarding the stopping/resuming of my
> camera stream with gstreamer. When I restart the stream by a
> transition from GST_STATE_PLAYING (1) -> GST_STATE_PAUSING (2)
> ->GST_STATE_ PLAYING (3), the stream contains the last frames from
> (1).
>
> Is there a proper way to clear the pipeline? I don’t want to see any
> old frames when I restart my stream.

Pause state is not often used for live pipelines, it will just block the rendering. Best is to cycle through NULL, or perhaps ready.

>
> I’ve also tried to send flushing events, but without success. I did
> this by sending the events gst_event_new_flush_start() and
> gst_event_new_flush_stop().
>
> My pipeline looks like this:
>
> udpsrc port=55555 caps=\"application/x-rtp, media=(string)video,
> clock-rate=(int)90000, encoding-name=(string)H264, payload=(int)96\"

It might be wise to use rtpjitterbuffer here.

> ! rtph264depay
> ! avdec_h264
> ! decodebin
> ! videoconvert
> ! glupload
> ! appsink
>
> Advice is welcome.
>
> BR
> Michael
>
>
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