Set gstreamer rtsp latency=0

dahan

I want to play H.264 videos(rtsp protocol) with QMediaPlayer(Qt5.6.2 and Gstreamer1.8.1). It works but there is some latency about 2s.

When I play the rtsp video with gst-launch, I use the command that like```
//gst-launch-1.0 -v rtspsrc latency=0 location="rtsp://xx:554"


So. How could I add such parameter to QMediaPlayer? Maybe should I add something to the component QtMultiMedia?

dahan

@SGaist Thanks. When I use gst-launch-1.0 to play the video, I add the parameter "latency=0". and it plays almost real-time. So I want add such parameter to QMediaPlayer. I search the code of QtMultiMedia, and find that the file qgstreamerplayersession.cpp is about player. There is some code about "rtsp". I think the following code is important:

    } else if (qstrcmp(G_OBJECT_CLASS_NAME(G_OBJECT_GET_CLASS(source)), "GstRTSPSrc") == 0) { // line 1578
        //rtspsrc acts like a live source and will therefore only generate data in the PLAYING state.
        self->m_sourceType = RTSPSrc;
        self->m_isLiveSource = true;
        g_object_set(G_OBJECT(source), "buffer-mode", 1, NULL); // line 1583
        g_object_set(G_OBJECT(source), "latency", 0, NULL); // I add this line.Sorry to make a mistake above that I wrote wrong line number. It is not line 1586
        g_object_set(G_OBJECT(source), "threads", 4, NULL); // I add this line. I want to make QMediaPlayer work multi-thread.

I am sure that the code will execute because when I add "g_object_set(G_OBJECT(source), "threads", 4, NULL); " , there will be warning in the console that rtspsrc does not have property "threads".

SGaist

Hi and welcome to devnet,

AFAIK, you need to modify the QtMultimedia GStreamer backend for that to happen.

Kent-Dorfman

internet/IP/RTSP/UDP multimedia is not designed for zero latency. You are going to be dissappointed. There is ALWAYS inherent latency when streaming video over IP networks. In tightly controlled point-to-point configuration you might get it down to 100-150ms average latency but that's about as good as it gets.

dahan

@SGaist Thanks. I add "g_object_set(G_OBJECT(source), "latency", 0, NULL);" on line 1586 to the file qgstreamerplayersession.cpp, but it does not work.

SGaist

@dahan said in Set gstreamer rtsp latency=0:

but it does not work.

You know that with that high level of details it's mostly Crystal Ball debugging ?

dahan

@SGaist emm, I am so new with QtMultiMedia and Gstreamer that I just try.

SGaist

That has nothing to do with Qt or GStreamer. When asking a question, you should always give as much details as you can about what you tried, what you excepted, what you actually get, etc.

For example here: did you check if the methods you call have return values ? If so, did you check what they mean ?

dahan

@SGaist Thanks. When I use gst-launch-1.0 to play the video, I add the parameter "latency=0". and it plays almost real-time. So I want add such parameter to QMediaPlayer. I search the code of QtMultiMedia, and find that the file qgstreamerplayersession.cpp is about player. There is some code about "rtsp". I think the following code is important:

    } else if (qstrcmp(G_OBJECT_CLASS_NAME(G_OBJECT_GET_CLASS(source)), "GstRTSPSrc") == 0) { // line 1578
        //rtspsrc acts like a live source and will therefore only generate data in the PLAYING state.
        self->m_sourceType = RTSPSrc;
        self->m_isLiveSource = true;
        g_object_set(G_OBJECT(source), "buffer-mode", 1, NULL); // line 1583
        g_object_set(G_OBJECT(source), "latency", 0, NULL); // I add this line.Sorry to make a mistake above that I wrote wrong line number. It is not line 1586
        g_object_set(G_OBJECT(source), "threads", 4, NULL); // I add this line. I want to make QMediaPlayer work multi-thread.

I am sure that the code will execute because when I add "g_object_set(G_OBJECT(source), "threads", 4, NULL); " , there will be warning in the console that rtspsrc does not have property "threads".

SGaist

@dahan said in Set gstreamer rtsp latency=0:

g_object_get

I would check with a g_object_get call to see if the value was indeed set.

dahan

@SGaist Thanks a lot. I do check with g_object_get, and the property latency is setted successfully.
I find that QtMultiMedia use gstreamer plugin playbin. I play the video with command gst-launch-1.0 playbin latency=10 uri=rtsp://xx:554 . On my machine it does not play as good as gst-launch-1.0 rtspsrc latency=10 location=rtsp://xx:554. So I think it's problem of the gstreamer plugin "playbin". I will try replace playbin with rtspsrc in QtMultiMedia.