Hi,
For using timeoverlay and clockoverlay the frame data has to be copied from NVMM buffer to CPU buffer and then copied back to NVMM buffer. The performance can be better if the operations are eliminated. A possible solution is to link to nvivafilter and call cairo functions for putting time/clock information. May refer to this patch:
Tx2-4g r32.3.1 nvivafilter performance - #16 by DaneLLL
Since nvvidconv plugin is open source, you may also customize the plugin to call cairo functions. Can get buffer pointer by calling NvBufferMemMap()/NvBufferMemUnMap()
The source code is in
L4T Driver Package (BSP) Sources