Accessing video RGB data

[Sami Pietila]

Hi,

Thanks for reply! I changed to ximagesink and now I am getting RGB data.

I don't need to modify movie frames, but I need to read them and do
some calculations. Calculations might take some time, so I need a way
to control how gstreamers feeds the frames. That is, I need a way to
ask next frame from gstreamer instead of gstreamer feeding them at a
constant rate.

How can I get a new frame only when requested?

2011/10/4 Stefan Sauer <ensonic at hora-obscura.de>:
> On 10/01/2011 10:16 AM, Sami Pietila wrote:
>> Hi,
>>
>> I am trying to access RGB data of image frames in a mov -file. Below
>> is code that I have constructed using gstreamer examples and
>> documentation. cb_have_data() doesn't seem to give me RGB data. I am
>> setting the data to 0 (=black?), but I can see shortly a green screen
>> on the video and then comes invalid pointer error.
> when you see green on all 0, you are in a yuv format and not rgb. In the
> code below the ffmpegcolorspace wont convert anything as xvimagsink will
> prefer yuv. If you change the later to ximagesink you'll get RGB.
>
>> How can I read RGB data from a video, frame by frame? I need also a
>> way to control the flow of frames, in a way that once I have done with
>> processing one frame I could ask gstreamer to give me next frame. Code
>> examples would be great.
>
> If you wants to modify the image data you better write an element.
>
> Stefan
>
>> Thanks
>>
>>
>> #include <iostream>
>> #include <gst/gst.h>
>>
>> GstElement *pipeline, *video;
>>
>> static gboolean
>> cb_have_data (GstPad *pad, GstBuffer *buffer, gpointer u_data) {
>>
>>   guint16 *data = (guint16 *) GST_BUFFER_DATA (buffer);
>>   GstCaps *caps = gst_buffer_get_caps(buffer);
>>
>>   char m_width[] = "width";
>>   char m_height[] = "height";
>>
>>   GstStructure *structure = gst_caps_get_structure(caps, 0);
>>
>>   const GValue *width_gval = gst_structure_get_value(structure, m_width);
>>   const GValue *height_gval = gst_structure_get_value(structure, m_height);
>>
>>   int width = g_value_get_int (width_gval);
>>   int height = g_value_get_int(height_gval);
>>
>>   for (int y = 0; y < height; y++) {
>>         for (int x = 0; x < width; x++) {
>>                 data[width*y + x] = 0;
>>         }
>>   }
>>
>>   return TRUE;
>> }
>>
>> static void
>> cb_newpad (GstElement *decodebin,
>>          GstPad     *pad,
>>          gboolean    last,
>>          gpointer    data)
>> {
>>   GstCaps *caps;
>>   GstStructure *str;
>>   GstPad *videopad;
>>
>>   videopad = gst_element_get_static_pad (video, "sink");
>>   if (GST_PAD_IS_LINKED (videopad)) {
>>     g_object_unref (videopad);
>>     return;
>>   }
>>
>>   caps = gst_pad_get_caps (pad);
>>   str = gst_caps_get_structure (caps, 0);
>>   if (!g_strrstr (gst_structure_get_name (str), "video")) {
>>     gst_caps_unref (caps);
>>     gst_object_unref (videopad);
>>     return;
>>   }
>>   gst_caps_unref (caps);
>>
>>   gst_pad_link (pad, videopad);
>>
>>   g_object_unref (videopad);
>> }
>>
>> gint main (gint argc, gchar *argv[])
>> {
>>   GMainLoop *loop;
>>   GstElement *src, *dec, *filter, *cs, *sink;
>>   GstPad *videopad;
>>   GstBus *bus;
>>
>>   gst_init (&argc, &argv);
>>   loop = g_main_loop_new (NULL, FALSE);
>>
>>   pipeline = gst_pipeline_new ("pipeline");
>>
>>   bus = gst_pipeline_get_bus (GST_PIPELINE (pipeline));
>>
>>   src = gst_element_factory_make ("filesrc", "source");
>>   g_object_set (G_OBJECT (src), "location",
>> "/home/sammy/src/SamScanPlus/src/testi.mov", NULL);
>>   dec = gst_element_factory_make ("decodebin", "decoder");
>>   g_signal_connect (dec, "new-decoded-pad", G_CALLBACK (cb_newpad), NULL);
>>   gst_bin_add_many (GST_BIN (pipeline), src, dec, NULL);
>>   gst_element_link (src, dec);
>>
>>   video = gst_bin_new ("videobin");
>>   cs = gst_element_factory_make ("ffmpegcolorspace", "cs");
>>   videopad = gst_element_get_static_pad (cs, "sink");
>>   sink = gst_element_factory_make ("xvimagesink", "sink");
>>   gst_bin_add_many (GST_BIN (video), cs, sink, NULL);
>>   gst_element_link_many(cs, sink, NULL);
>>   gst_element_add_pad (video, gst_ghost_pad_new ("sink", videopad));
>>   gst_object_unref (videopad);
>>   gst_bin_add (GST_BIN (pipeline), video);
>>
>>   GstPad *pad = gst_element_get_pad (cs, "src");
>>   gst_pad_add_buffer_probe (pad, G_CALLBACK (cb_have_data), NULL);
>>   gst_object_unref (pad);
>>
>>   gst_element_set_state (pipeline, GST_STATE_PLAYING);
>>   g_main_loop_run (loop);
>>
>>   gst_element_set_state (pipeline, GST_STATE_NULL);
>>   gst_object_unref (GST_OBJECT (pipeline));
>>
>>   return 0;
>> }
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