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image/jpeg format with v4l2 webcam

Hello, everyone.  I am using gstreamer (through gst-launch) to access my
v4l2 webcam (I have two - Logitech QuickCam for Notebooks Pro & Logitech
QuickCam Pro 5000), both of which work perfectly fine when using
video/x-raw-yuv-type pixel formats.

However, when I want to capture the video using the supported image/jpeg
pixel formats, which I presume would be higher quality (if I dump
straight to JPEG/MJPEG files) as no implicit conversion is happening, I
get framerates much lower than expected.

For example, my webcams claim to support up to 30 frames per second when
capturing in the image/jpeg format.  But the resulting video is much,
much slower.  And this scales, somehow, if I change the capture
framerate.  So, for example, if I specify 25 fps, it's slower than the
30, and 15 is slower than 25, etc.  But all of these are much slower in
terms of capture than their yuv-format counterparts.

Could someone guide me as to how I can find the source of this problem
and/or test different settings that might work?


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