Hi @Javi,
that fix an issue similar to this one. You may need to try a few different options in the video decoding settings (click purple QGC logo in the top left, then Application Settings - the video decode priority is near the bottom of the top box).
If that doesn’t fix the issue, can you provide some more information on how you’re powering the ROV, as well as what you’re using to convert that for the 5V electronics? Some of our older ROVs used a 5V3A converter, whereas we now use and recommend a 5V6A converter.