linking filters with caps

[Krzysztof Konopko]

Hi Chuck,

I guess you're using x264enc.

For the "format" capability you should use GST_TYPE_FOURCC rather than
G_TYPE_STRING even though the documentation says it's string (that's why
it's still ugly I guess :)
http://gstreamer.freedesktop.org/data/doc/gstreamer/head/gst-plugins-ugly-plugins/html/gst-plugins-ugly-plugins-x264enc.html

If you try to run your app with GST_DEBUG=GST_CAPS:4 you should see
something like this (among others):

0:00:00.076610990  2450  0x9751aa0 DEBUG               GST_CAPS
gstutils.c:913:gst_element_get_compatible_pad_template: intersecting
video/x-raw-yuv, format=(string)I420, width=(int)720, height=(int)480,
framerate=(fraction)30/1
0:00:00.076628924  2450  0x9751aa0 DEBUG               GST_CAPS
gstutils.c:915:gst_element_get_compatible_pad_template: ..and
video/x-raw-yuv, format=(fourcc){ I420, YV12 }, framerate=(fraction)[
0/1, 2147483647/1 ], width=(int)[ 16, 2147483647 ], height=(int)[ 16,
2147483647 ]
0:00:00.076652937  2450  0x9751aa0 DEBUG               GST_CAPS
gstutils.c:921:gst_element_get_compatible_pad_template: caps are not
compatible

The catch here is the "fourcc" type not matching requested "string" type
while everything else seem to match when intersecting caps.

Even better approach is to try gst-launch in such situation. The
following helped me to prove my theory (no errors when using fourcc type):

gst-launch videotestsrc ! 'video/x-raw-yuv, format=(fourcc)I420,
width=(int)720, height=(int)480, framerate=(fraction)30/1' ! x264enc
tune=4 byte-stream=true bitrate=1024 ! fakesink

Kris

On 01/11/12 21:23, Chuck Crisler wrote:
> Please help! I am stumped and confused by the terminology. I am using
> GStreamer 0.10.(not sure). I am trying to capture from V4l2 and feed into
> an H264 encoder (hardly novel). I want to specify the capture size and
> format (I420). So I setup a caps filter. Here is a snipit of my code.
> 
>       g_object_set (G_OBJECT (source_), "device",
> inputOptions_.ParameterDetails.adapter.cDevice,
>                     "always-copy", FALSE, NULL);
>       GstCaps *pSrcCaps = gst_caps_new_simple("video/x-raw-yuv",
>           "format", G_TYPE_STRING, "I420", "width", G_TYPE_INT, 720,
> "height", G_TYPE_INT, 480,
>           "framerate", GST_TYPE_FRACTION, 30, 1, NULL);
> 
>       // Initialize the encoder.
>       g_object_set (G_OBJECT (encoder_), "tune", (guint)4,  // zerolatency
>                     "byte-stream", (gboolean)TRUE,
>                     "bitrate",
> (guint)inputOptions_.ParameterDetails.adapter.iTransmitBitrate, NULL);
> ...
> 
>       // Add the elements to the pipeline.
>       gst_bin_add_many(GST_BIN(mainPipeline_), source_, encoder_, muxer_,
> sink_, NULL);
>       // Link the pipeline together.
>       bRet = gst_element_link_filtered(source_, encoder_, pSrcCaps);
>       gst_caps_unref(pSrcCaps);
>       if (!bRet)
>       {
>          GST_DEBUG("Failed to link filtered elements in pipeline.");
>          return bRet;
>       }
> 
> It is complaining that it can't link the video source to the encoder with
> my caps filter.
> 
> Here is a snipit of the log.
> 
> gstutils.c:1585:gst_element_link_pads: trying to link element
> VideoSrc:(any) to element capsfilter0:sink
> Nov  1 17:08:39 0:00:00.064704777 22354  0x88462d8
> INFO        GST_ELEMENT_PADS
> gstelement.c:944:gst_element_get_static_pad: found pad capsfilter0:sink
> Nov  1 17:08:39 0:00:00.064792569 22354  0x88462d8
> INFO                GST_PADS
> gstutils.c:1493:prepare_link_maybe_ghosting: VideoSrc and capsfilter0
> in same bin, no need for ghost pads
> Nov  1 17:08:39 0:00:00.064950133 22354  0x88462d8
> INFO                GST_PADS
> gstpad.c:1886:gst_pad_link_prepare: trying to link VideoSrc:src and
> capsfilter0:sink
> Nov  1 17:08:39 0:00:00.069477022 22354  0x88462d8
> INFO                GST_PADS
> gstpad.c:2059:gst_pad_link: linked VideoSrc:src and capsfilter0:sink,
> successful
> Nov  1 17:08:39 0:00:00.069674954 22354  0x88462d8
> INFO        GST_ELEMENT_PADS
> gstutils.c:1585:gst_element_link_pads: trying to link element
> capsfilter0:src to element VideoEncoder:(any)
> Nov  1 17:08:39 0:00:00.069755204 22354  0x88462d8
> INFO        GST_ELEMENT_PADS
> gstelement.c:944:gst_element_get_static_pad: found pad capsfilter0:src
> Nov  1 17:08:39 0:00:00.069826303 22354  0x88462d8
> INFO                GST_PADS
> gstutils.c:1046:gst_pad_check_link: trying to link capsfilter0:src and
> VideoEncoder:src
> Nov  1 17:08:39 0:00:00.069883154 22354  0x88462d8
> INFO                GST_PADS
> gstutils.c:1066:gst_pad_check_link: Sink pad VideoEncoder:src is not
> sink pad, failed
> Nov  1 17:08:39 0:00:00.069939587 22354  0x88462d8
> INFO                GST_PADS
> gstutils.c:1046:gst_pad_check_link: trying to link capsfilter0:src and
> VideoEncoder:sink
> Nov  1 17:08:39 0:00:00.084800392 22354  0x88462d8
> INFO        GST_ELEMENT_PADS
> gstutils.c:1209:gst_element_get_compatible_pad:<VideoEncoder> Could
> not find a compatible pad to link to capsfilter0:src
> Nov  1 17:08:39 0:00:00.084907739 22354  0x88462d8
> INFO                 default
> gstutils.c:1873:gst_element_link_pads_filtered: Could not link elements
> 
> 
> Can anyone see my (probably silly/simple) mistake and point me in the right
> direction?
> 
> Thank you very much!
> 
> 
> 
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