[gst-devel] Why does this video format conversion fail?

[Timothy Braun]

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

On Fri, Dec 10, 2010 at 12:13 PM, wally_bkg <wb666greene at gmail.com> wrote:

>
>
> 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:
> http://gstreamer-devel.966125.n4.nabble.com/Why-does-this-video-format-conversion-fail-tp3080822p3082344.html
> Sent from the GStreamer-devel mailing list archive at Nabble.com.
>
>
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