Hi,
Raw h265 stream may not contain correct fps information. Please try
gst-launch-1.0 v4l2src device=/dev/video0 io-mode=2 ! 'image/jpeg,width=1920,height=1080,framerate=60/1' ! nvv4l2decoder mjpeg=1 ! nvv4l2h265enc ! h265parse ! matroskamux ! filesink location=a.mkv
There is an issue of decoding YUV422 MJPEG. Please try the prebuilt lib:
https://elinux.org/Jetson/L4T/r32.4.x_patches
[GSTREAMER]Prebuilt lib for decoding YUV422 MJPEG through nvv4l2decoder