Multiple camera streams and v4l2src

[Vincent Bossier]

When connecting two webcams to my Linux computer (Ubuntu 9.04), I try
to visualize both streams simultaneously with the following commands:

gst-launch v4l2src device=/dev/video0 ! xvimagesink
gst-launch v4l2src device=/dev/video1 ! xvimagesink

The first command leads well to a window displaying the video stream
from the first camera. The second command leads to a scrambled video
with the following error logs in the shell:

Setting pipeline to PAUSED ...
Pipeline is live and does not need PREROLL ...
Setting pipeline to PLAYING ...
New clock: GstSystemClock
libv4lconvert: Error decompressing JPEG: fill_nbits error: need 3 more bits
libv4lconvert: Error decompressing JPEG: fill_nbits error: need 1 more bits
libv4lconvert: Error decompressing JPEG: fill_nbits error: need 4 more bits
libv4lconvert: Error decompressing JPEG: fill_nbits error: need 1 more bits
libv4lconvert: Error decompressing JPEG: fill_nbits error: need 2 more bits
libv4lconvert: Error decompressing JPEG: fill_nbits error: need 5 more bits

When launched one at a time, each command is successfull.

Is there a known limitation preventing to display two video pipelines
(coming from v2lsrc?) at the same time?

Thank you,

Vincent

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[Filippo]

On Thu, Jun 18, 2009 at 9:51 PM, Vincent
Bossier<[hidden email]> wrote:

> When connecting two webcams to my Linux computer (Ubuntu 9.04), I try
> to visualize both streams simultaneously with the following commands:
>
> gst-launch v4l2src device=/dev/video0 ! xvimagesink
> gst-launch v4l2src device=/dev/video1 ! xvimagesink
>
> The first command leads well to a window displaying the video stream
> from the first camera. The second command leads to a scrambled video
> with the following error logs in the shell:
>
> Setting pipeline to PAUSED ...
> Pipeline is live and does not need PREROLL ...
> Setting pipeline to PLAYING ...
> New clock: GstSystemClock
> libv4lconvert: Error decompressing JPEG: fill_nbits error: need 3 more bits

Did you connect them to the same controller? Probably two webcam
streams at once exceed the USB bandwidth.
Try with another usb port or set caps to use a lower resolution (or framerate).
HTH,

Filippo

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