Even with the best tools, some videos will fail to download. The most common reasons are:
I notice you're asking about downloading private videos from ThisVid. I should clarify a few important points: thisvid private video downloader
Uploaded content can be marked as either (visible to all visitors) or private (visible only to approved friends). This binary privacy system is at the heart of why “private video downloaders” are sought after and why the topic requires careful handling. Even with the best tools, some videos will fail to download