I am trying to stream frames using OpenCV and Gstreamer in Python. I'm on a 64 bit Bulseye Raspberry Pi 4. This is the pipeline I am using on the Raspberry:
pipeline = 'appsrc ! "video/x-raw,framerate=25/1,format=BGR,width=640,height=480" ! ' \
'queue ! v4l2h264enc ! "video/x-h264,level=(string)4" ! h264parse ! ' \
'rtph264pay ! gdppay ! tcpserversink host=0.0.0.0 port=7000 '
cv2.VideoWriter(pipeline, cv2.CAP_GSTREAMER, 0, args.fps, (args.width, args.height))
It seems to be some problem with v4l2h264enc. Enabling GST_DEBUG=4 gives me
0x3e39a00 ERROR GST_PIPELINE gst/parse/grammar.y:1007:priv_gst_parse_yyparse: no source element for URI "/x-raw,framerate=25/1,format=BGR,width=640,height=480""
0:00:00.087855767 92892 0x3e39a00 ERROR GST_PIPELINE gst/parse/grammar.y:1007:priv_gst_parse_yyparse: no source element for URI "/x-h264,level=(string)4""
These two errors look most important to me, but you can see the full log here.
Using a similar CLI pipeline the stream connects just fine (except for some encoding grayness, which isn't the most critical to me right now).
# Stream
gst-launch-1.0 v4l2src device=/dev/video0 ! \
'video/x-raw,framerate=30/1,format=UYVY,width=1280,height=720' ! \
v4l2h264enc ! 'video/x-h264,level=(string)4' ! h264parse ! \
rtph264pay config-interval=1 pt=96 ! gdppay ! tcpserversink host=0.0.0.0 port=7000
# Client
sudo gst-launch-1.0 -v tcpclientsrc host=yraspberry ip> port=7000 ! \
gdpdepay ! rtph264depay ! avdec_h264 ! videoconvert ! \
autovideosink sync=false
With appsrc and opencv I also tried writing to a file without success.
The opencv library is compiled with Gstream support. This is what I get from cv2.getBuildInformation():
Video I/O:
DC1394: NO
FFMPEG: YES
avcodec: YES (58.91.100)
avformat: YES (58.45.100)
avutil: YES (56.51.100)
swscale: YES (5.7.100)
avresample: NO
GStreamer: YES (1.18.4)
v4l/v4l2: YES (linux/videodev2.h)
Any help would be most welcome!
As mentioned by @SeB, the BGR frames might not be supported by v4l2h264enc. And leads to this error, which videoconvert fixes:
opencv/opencv/modules/videoio/src/cap_gstreamer.cpp (2293) writeFrame OpenCV | GStreamer warning: Error pushing buffer to GStreamer pipeline
But the main cause for the no source element for URI errors turned out to be the double quotes around video/x-raw and video/x-h264.
This is the final pipeline that works.
pipeline = 'appsrc ! videoconvert ! v4l2h264enc ! video/x-h264,level=(string)4 ! ' \
'h264parse ! matroskamux ! tcpserversink host=0.0.0.0 port=7000 '
Also, as @SeB suggested, I also included the matroskamux instead of rtph264pay ! gdppay, since it gives better stream performance.