Hi,
Please check capability of video decoders in development guide.
It supports single 4Kp60. For multiple video decoding, you may try 4 1080p60.
We never verify 128 video decoding threads, you may try but the resolution has to be small like 320x240.
In running 06_jpeg_decode, JPEG files are sequentially decoded, not simultaneously. So you can set file number arbitrarily.