Why is videobox/videomixer dropping frames?

[Stefan Kost]

On 08/11/11 17:01, wally bkg wrote:
> I need binocular video for an image processing application, so it
> seemed logical to "stack" cameraR and cameraL into a single frame
> using videobox and videomixer and then pass that into my appsink for
> processing as a single buffer.
>
> Unfortunately performance is terrible with jerky video and occasional
> messages about dropped frames.  Using Ubuntu 10.04 64-bit, all patches
> as of this morning and its "stock" gstreamer-0.10.28 setup on an AMD
> quad core processor with 8GB RAM.  (I had tried the PPA version a
> while back, but it hosed my system, recovering was a PITA so I'm not
> amenable to trying it again!)
>
> Sample pipeline with gst-launch:
>
> gst-launch v4l2src device=/dev/video1 ! ffmpegcolorspace !
> video/x-raw-yuv,format=\(fourcc\)AYUV,width=640,height=480 !\
>  videobox border-alpha=0 top=-480 bottom=-48 ! videomixer name=mix
> sink_0::alpha=1.0 sink_1::alpha=1.0 ! ffmpegcolorspace !\
>  xvimagesink  v4l2src device=/dev/video0 ! ffmpegcolorspace !
> video/x-raw-yuv,format=\(fourcc\)AYUV,width=640,height=480 !\
>  ffmpegcolorspace ! mix.
>
Do without videobox and use sink_0:xpos and sink_0:ypos properties on
videomixer. Maybe try to avoid the AYUV conversion, if you don't want to
blend.

Stefan

>
> But running two instances gives smooth video despite using
> significantly more CPU according to top:
>
> gst-launch v4l2src device=/dev/video1 ! ffmpegcolorspace !
> video/x-raw-yuv,format=\(fourcc\)AYUV,width=640,height=480 !\
>  ffmpegcolorspace ! xvimagesink  v4l2src device=/dev/video0 !
> ffmpegcolorspace !\
>  video/x-raw-yuv,format=\(fourcc\)AYUV,width=640,height=480 !
> ffmpegcolorspace ! xvimagesink
>
> I've 5 different v4l2 capture devices (two PCI and 3 USB) and all
> pairs have the perfromance problem including one USB device that has
> two full frame rate capture inputs (Sensoray 2255S).  All pairings
> give smooth video with two instances.
>
> The video has perfect "genlock" as its one VCR output fed to the
> capture devices with a distribution amplifier.  The 48 extra scan
> lines at the bottom of the stacked frames I planned to fill with
> barcoded metadata, removing them didn't change anything.  In fact I
> can run both gst-launch commands from separate terminal windows and
> its very obvious when the videobox/videomixer drops frames.
>
> Is there something I'm missing that can fix this?  The two cameras in
> a single buffer would seem to make the downstream code much more
> understandable, but I can use the two instance solution.
>
> Any rational reason why videobox supports video/x-raw-gray and
> videomixer does not?
>
>
>
>
>
>
>
>
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