Wally, Theres other parts to the negotiation besides color space. Framerate and size are also considered. You may want to make it resemble: gst-launch v4l2src device=/dev/video1 ! ffmpegcolorspace ! videoscale ! videorate ! video/x-raw-yuv, framerate=\(fraction\)30000/1001, width=640, height=480 ! ffmpegcolorspace ! xvimagesink I don't think the second ffmpegcolorspace is needed either. If you run this with GST_DEBUG=GST_CAPS:3, you will see the logs of the negotiations and you can hopefully decipher whats happening. Hope this helps. Tim <div class="gmail_quote">On Fri, Dec 10, 2010 at 12:13 PM, wally_bkg <<a href="mailto:wb666greene@gmail.com">wb666greene@gmail.com</a>> wrote: <blockquote class="gmail_quote" style="margin: 0pt 0pt 0pt 0.8ex; border-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"> wally_bkg wrote: > > I need to do it in C but I can illustrate the problem simply with a few > gst-lanuch commands. > > Basically I have a USB video capture device (Hauppauge WinTV-HVR 950Q) > that works with gstreamer if I simply do: > > gst-launch v4l2src device=/dev/video2 ! xvimagesink > > However I'm having trouble figuring out a caps filter to use that will let > me get the buffers in a yuv type format. > > > On a normal capture card if I do: > > gst-launch v4l2src device=/dev/video1 ! video/x-raw-yuv, > framerate=\(fraction\)30000/1001, width=640, height=480 ! xvimagesink > > It works fine, but change to /dev/video2 (the USB device) I get: > > Setting pipeline to PAUSED ... > ERROR: Pipeline doesn't want to pause. > ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: Could not > negotiate format > Additional debug info: > gstbasesrc.c(2719): gst_base_src_start (): > /GstPipeline:pipeline0/GstV4l2Src:v4l2src0: > Check your filtered caps, if any > > > > So I tried using ffmpegcolorspace to convert: > > gst-launch v4l2src device=/dev/video1 ! ffmpegcolorspace ! > video/x-raw-yuv, framerate=\(fraction\)30000/1001, width=640, height=480 ! > ffmpegcolorspace ! xvimagesink > > And get the same error message as without the ffmpegcolorspace elements > between the capsfilter. > > > One of my main reasons for trying to use gstreamer is to let it do the > heavy lifting of dealing with video input and output. At the end of the > day all I want from the appsink element is a pointer to the video data in > a format documented well enough that I can pull out a 640x480 intensity > (grayscale) image. > > Up to getting this device, setting the caps to { video/x-raw-yuv, > framerate=\(fraction\)30000/1001, width=640, height=480 } has worked fine > for all the capture cards I've tried, and obviously needing to deal with > only a single raw format in my code simplifies it greatly. > > > I'm having trouble in my C code to extract the caps that get negotiated if > I leave out the capsfilter from my pipeline. Any samples out there of how > to do it? > > I figured out how to extract the caps. When using /dev/video1 (saa713x card) the "default" Buffer caps: video/x-raw-gray, bpp=(int)8, framerate=(fraction)30000/1001, width=(int)704, height=(int)480 When uisng /dev/video2 (the 950Q USB device) Buffer caps: video/x-raw-rgb, bpp=(int)24, depth=(int)24, red_mask=(int)255, green_mask=(int)65280, blue_mask=(int)16711680, endianness=(int)4321, framerate=(fraction)30000/1001, width=(int)720, height=(int)480 But this doesn't give me any clues as to why ffmpegcolor space can't convert the rgb caps to the yuv or grey caps I'd prefer to use. -- View this message in context: <a href="http://gstreamer-devel.966125.n4.nabble.com/Why-does-this-video-format-conversion-fail-tp3080822p3082344.html" target="_blank">http://gstreamer-devel.966125.n4.nabble.com/Why-does-this-video-format-conversion-fail-tp3080822p3082344.html</a> Sent from the GStreamer-devel mailing list archive at Nabble.com. ------------------------------------------------------------------------------ Oracle to DB2 Conversion Guide: Learn learn about native support for PL/SQL, new data types, scalar functions, improved concurrency, built-in packages, OCI, SQL*Plus, data movement tools, best practices and more. <a href="http://p.sf.net/sfu/oracle-sfdev2dev" target="_blank">http://p.sf.net/sfu/oracle-sfdev2dev</a> _______________________________________________ gstreamer-devel mailing list <a href="mailto:gstreamer-devel@lists.sourceforge.net">gstreamer-devel@lists.sourceforge.net</a> <a href="https://lists.sourceforge.net/lists/listinfo/gstreamer-devel" target="_blank">https://lists.sourceforge.net/lists/listinfo/gstreamer-devel</a> </blockquote></div>