Hi,
We don’t support lossless encoding in gstreamer now. Please use jetson_multimedia_api. Here are two relevant topics:
Lossless H264/HEVC - #3 by DaneLLL
Can tx2nx decode YUV444? - #3 by DaneLLL
You have to convert frame data into YUV444. For lossless encoding, only YUV444 is supported.