Giving a video response is considered by respondents to be a premium response and, in turn, many want to be incentivised accordingly. An additional incentive for recording a video is recommended.
If you are incentivising the user, make sure you give details about the incentive at the beginning of the survey and at the opt-in page. You will need to be very clear about what is expected in return for this payment. Where this has not been spelt out clearly we have seen some undesirable behaviour such as participants just videoing themselves sitting silently, submitting videos of <5 secs or uploading irrelevant content - by making this clear up front you encourage them to submit valuable content and avoid having to reward users for unusable content.