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

Thu Sep 10 07:02:05 UTC 2020

Hi all,

unfortunately I couldn't find any solution regarding my problem. What I basically want is to clear/drop the buffers of a live stream pipeline in case of the pausing/ready state. GST_STATE_NULL didn't solve the problem. Even if I create a complete new pipeline and delete the previous one I still get the old frames (this is really strange, isn't it?). Sending events to flush the pipeline has also no effect.

Is it really that hard to clear the pipeline? :-(

A colleage of mine evaluated this problem in a pipeline without glupload and appsink. He could stop and restart the stream with state changes and flushing events. Maybe the problem is located in glupload or appsink? Do I miss a configuration option?

This mailing-list post describes the same/a similar problem: http://gstreamer-devel.966125.n4.nabble.com/Dropping-buffers-when-pausing-live-stream-td974106.html

Unfortunately there is no solution posted.

Advice is really appreciated.

Thx in advance,
Michael

-----Ursprüngliche Nachricht-----
Von: Timtchenko, Michael
Gesendet: Montag, 7. September 2020 09:03
An: 'Discussion of the development of and with GStreamer' <gstreamer-devel at lists.freedesktop.org>
Betreff: AW: [External] Re: Restarted stream contains legacy frames

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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