Framerate issue with v4l2sink

[Nicolas Dufresne]

Le mardi 24 mars 2020 à 18:10 +0000, Lenz, Mika a écrit :
> We are streaming data from appsrc into a v4l2sink. Therefore, we are
> using v4l2loopback on /dev/videoX. The camera has a fix resolution of
> 640x480 and a variable framerate. The framerate is set up at the
> beginning with a library provided by the manufacturer. The data is 16
> Bit Gray LE.
> 
> The problem is, that Gstreamer always wants to put 33 frame per
> second into the sink. So, if we choose 60fps, it’s 33fps and if we
> choose 30fps, it isn’t working. Every value bigger than 33fps is
> working, but only 33fps in real and every value lower than 33 fps is
> not working at all.
> 
> Before this, we already set the framerate and pushed data into a
> multifilesink or a udpsink with correct frame rate at the end. So,
> the initialization should not be the problem. Is there anything
> special to remind working with v42sink and v4l2loopback?

Appart that v4l2loopback driver should be rewritten from scratch in
order to make it work properly, no.

On a more serious note, what GStreamer does is list the frame interval
advertise by your driver. So if 33fps is the only thing you manage to
get to negotiate with v4l2sink/v4l2loopback, I'd first analyze the
driver. This driver have had issues from over a decade, including
buffer overflow and all the things you don't want in your product. So I
wouldn't be surprise if more bugs exist in regard to frame interval
handling.

> 
> This is from our application, I removed error checks etc:
> 
> cb_need_data (GstElement *appsrc,
>           guint       unused_size,
>           gpointer    user_data)
> {
>   static GstClockTime timestamp = 0;
>   GstBuffer *buffer;
>   GstFlowReturn ret;
>    
>   GstMapInfo map;
>   eDALProxy640USBErr eReturnCode;
>  
>   buffer = gst_buffer_new_and_alloc(IRIMAGE_NBPIXELS*2); //allocate 2
> Bytes for every pixel
>   if(gst_buffer_map (buffer, &map, GST_MAP_WRITE)) {
> while(true)
>          {
>              eReturnCode = Proxy640USB_GetImage(m_Handle, (short
> unsigned int*)map.data, paMeta, GETIMAGE_TIMEOUT);
>              if (eReturnCode == eProxy640USBSuccess)
>                     break;
>          }
>   }
>  
>   GST_BUFFER_PTS (buffer) = timestamp;
>   GST_BUFFER_DURATION (buffer) = gst_util_uint64_scale_int (1,
> GST_SECOND, 33);
>  
>   timestamp += GST_BUFFER_DURATION (buffer);
>   g_signal_emit_by_name (appsrc, "push-buffer", buffer, &ret);
>   gst_buffer_unmap(buffer, &map);
>   gst_buffer_unref(buffer);
> }
>  
>  
> gint main (gint argc, gchar *argv[])
> {
> sprintf(DEVICE, "/dev/video0");
> // GStreamer
>   GstElement *pipeline, *converter, *videosink, *videosrc, *appsrc;
>   gst_init (&argc, &argv);
>   loop = g_main_loop_new (NULL, FALSE);
>  
> // LWIR device
>   m_Handle = NULL;
>   eAGCProcessingValue agcVal = eAGCEnhanced;
>   eDALProxy640USBErr eReturnCode;
>   eReturnCode = Proxy640USB_GetModuleCount(&iCount);
>  
> // Connect to LWIR
> eReturnCode = Proxy640USB_ConnectToModule(0, &m_Handle);
>  
> // Set Processing depending of parameters
> (NUC/AGC/Shutterless/Framerate)
>   Proxy640USB_SetNUCProcessing(m_Handle, bBP, nuc);
>   Proxy640USB_SetShutterLessProcessing(m_Handle, bSL);
>   Proxy640USB_SetFloatFeature(m_Handle, efFrameRate, FRAMERATE);
>   Proxy640USB_SetAGCProcessing(m_Handle, agcVal);
>   Proxy640USB_SetUIntFeature(m_Handle, eiVideoUSBOutActivation, 1);
>  
> // Setup Pipeline
>   pipeline = gst_pipeline_new ("LWIR-streamer");
>   appsrc = gst_element_factory_make ("appsrc", "source");
>   videosrc = gst_element_factory_make("videotestsrc", "source");
>   converter = gst_element_factory_make ("videoconvert", "converter");
>   videosink = gst_element_factory_make ("v4l2sink", "videosink");
>   g_object_set (videosink, "device", DEVICE, NULL);
>  
> // Setting Capabilities
>   g_object_set (G_OBJECT (appsrc), "caps",
>         gst_caps_new_simple ("video/x-raw",
>                      "format", G_TYPE_STRING, "GRAY16_LE",
>                      "width", G_TYPE_INT, IRIMAGE_WIDTH,
>                      "height", G_TYPE_INT, IRIMAGE_HEIGHT,
>                      "framerate", GST_TYPE_FRACTION, FRAMERATE, 1,
>                      NULL), NULL);
>  
>   gst_bin_add_many (GST_BIN (pipeline), appsrc, converter,
> videosink,NULL);
>   gst_element_link_many (appsrc, converter, videosink, NULL);
>  
> // Setup appsrc to cd_need_data
>   g_object_set (G_OBJECT (appsrc),
>         "stream-type", 0,
>         "format", GST_FORMAT_TIME, NULL);
>   g_signal_connect (appsrc, "need-data", G_CALLBACK (cb_need_data),
> NULL);
>  
>   /* play */
>   gst_element_set_state (pipeline, GST_STATE_PLAYING);
>   g_main_loop_run (loop);
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