massively reduce input lag by reducing buffer size in gstreamer appsink

[tensorturtle]

See https://forums.developer.nvidia.com/t/how-to-eliminate-gstreamer-camera-buffer/75608/6

Fixes #XX

Description

Limiting buffer size and enabling gstreamer appsink to drop old frames decreases glass-to-glass lag significantly. My Jetson Nano 4GB + Raspberry Pi V2 camera went from around half a second to no noticeable delay.

Please see https://forums.developer.nvidia.com/t/how-to-eliminate-gstreamer-camera-buffer/75608/6 for the discussion.

Other information

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• [x] I added tests for the changes I made (if applicable).
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• [x] I tried running the project locally and verified that there are no visible errors.

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[IRyo-2021]

Thank you sooooo much! That really helped me to solve the latency problem.