Digitize RGB video using DE0-Nano

Your code is re-syncing the outgoing HSYNC with every incoming HSYNC pulse. So, you are seeing inter-row jitter - i.e. the entire row is moving with respect to an adjacent row. This you can see in the video you posted.

You must re-sync your counters once and only once per VSYNC cycle only. Having done this you must play the data out of your buffer using your internal timers only. This is the 'free running' that Tricky refers to. Don't reset them until the next VSYNC pulse. Any difference in the clock rate will be hidden in the VSYNC dead time, where it doesn't matter.

Cheers,

Alex