gstreamer libcamerasrc should set custom frame metadata

[bringert]

It would be nice to have access to all the libcamera metadata for each frame as buffer metadata in gstreamer.

Example per-frame metadata available from libcamera:

$ rpicam-vid -t 500 -n --metadata /tmp/test-meta.txt --metadata-format txt -o /tmp/test.h264 && awk 'NF==0{exit} {print}' /tmp/test-meta.txt
ExposureTime=29984
AnalogueGain=1.587597
FrameDuration=33327
SensorTemperature=32.000000
AeState=2
LensPosition=1.729818
DigitalGain=1.000936
Lux=153.352692
ColourGains=[ 1.965870, 1.733057 ]
ColourTemperature=5006
SensorBlackLevels=[ 4096, 4096, 4096, 4096 ]
FocusFoM=702
ColourCorrectionMatrix=[ 1.541116, -0.372801, -0.168312, -0.279741, 1.649470, -0.369722, 0.003117, -0.522662, 1.519555 ]
AfState=2
AfPauseState=0
ScalerCrop=(1152, 432)/2304x1728
FrameWallClock=1776423020743381760
SensorTimestamp=8303502247000

It looks like libcamerasrc currently only adds GstVideoMeta metadata to the buffers it produces.

[naushir]

I'm not at all familiar with gstreamer, so not sure what's involved with implementing this. Although I do agree this is something useful to have. Would you be able to post your question on the libcamera developer mailing list - folks there will be more knowledgeable about libcamerasrc and what may be needed for your request.