Why is videobox/videomixer dropping frames?

[Josh Doe]

You definitely need to insert queue's between the v4l2src's and the
videomixer.
-Josh

On Thu, Aug 11, 2011 at 11:01 AM, wally bkg <wb666greene at gmail.com> 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.
>
>
> 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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>
>
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