<html> <head> <meta http-equiv="content-type" content="text/html; charset=UTF-8"> </head> <body> If I want to send a video stream on /dev/video4 to a loopback device in Ubuntu I can use : ./gst-launch-1.0 -v -m v4l2src device=/dev/video4 ! v4l2sink device=/dev/video0 And the video on /dev/video4 can be seen with : ffplay /dev/video0 I can merge 2 videos with: <pre class="western" style="margin-bottom: 0.5cm">./gst-launch-1.0 v4l2src device=/dev/video4 ! videoscale ! queue ! videoconvert ! video/x-raw, format=YUY2, framerate=30/1, width=640, height=480! alpha alpha=1 ! videobox border-alpha=0 left=-640 ! compositor name=Mix ! videoconvert ! autovideosink v4l2src device=/dev/video2 ! videoscale ! queue ! videoconvert ! video/x-raw, format=YUY2, framerate=30/1, width=640, height=480! alpha alpha=1 ! videobox border-alpha=0 right=-640 ! Mix. And see the merged camera videos on my monitor but I can't seem to send those merged videos to a loopback device. For example if I try changing autovideosink to v4l2sink device=/dev/video0: ./gst-launch-1.0 v4l2src device=/dev/video4 ! videoscale ! videoconvert ! video/x-raw, format=YUY2, framerate=30/1, width=640, height=480! alpha alpha=1 ! videobox border-alpha=0 left=-640 ! videomixer name=Mix ! videoconvert ! v4l2sink device=/dev/video0 sync=false v4l2src device=/dev/video2 ! videoscale ! videoconvert ! video/x-raw, format=YUY2, framerate=30/1, width=640, height=480! alpha alpha=1 ! videobox border-alpha=0 right=-640 ! Mix. I get the following result with no video output: Setting pipeline to PAUSED ... Pipeline is live and does not need PREROLL ... Setting pipeline to PLAYING ... New clock: GstSystemClock ERROR: from element /GstPipeline:pipeline0/GstV4l2Src:v4l2src1: Internal data stream error. Additional debug info: gstbasesrc.c(3072): gst_base_src_loop (): /GstPipeline:pipeline0/GstV4l2Src:v4l2src1: streaming stopped, reason not-negotiated (-4) Execution ended after 0:00:00.381495593 Setting pipeline to PAUSED ... Setting pipeline to READY ... Setting pipeline to NULL ... Freeing pipeline ... I have also tried not specifying a video format as I have in my first example above but get the same error. Does anyone know how I can send my merged stream to the loopback device? Thanks Jim <style type="text/css">pre { background: transparent } pre.western { font-family: "Liberation Mono", monospace; font-size: 10pt } pre.cjk { font-family: "Noto Sans Mono CJK SC", monospace; font-size: 10pt } pre.ctl { font-family: "Liberation Mono", monospace; font-size: 10pt } p { margin-bottom: 0.25cm; line-height: 115%; background: transparent } strong { font-weight: bold }</style><pre class="western" style="margin-bottom: 0.5cm"></pre></pre> <style type="text/css"> pre { background: transparent } pre.western { font-family: "Liberation Mono", monospace; font-size: 10pt } pre.cjk { font-family: "Noto Sans Mono CJK SC", monospace; font-size: 10pt } pre.ctl { font-family: "Liberation Mono", monospace; font-size: 10pt } p { margin-bottom: 0.25cm; line-height: 115%; background: transparent } strong { font-weight: bold }</style> </body> </html>