jonasob
commented
8 years ago Ah, and here's another interesting tidbit when it comes to video files:
- Frame counts will vary. If you recode a video file, there's a big chance that the exact number of frames will change. I wouldn't actually have expected this, but I've seen upwards of 1.5% variation between formats, even if the fps remains the same.
bbhopesh
We're looking to extend the blockhash software to cover videos in addition to the images it already processes. There are existing alternatives for this, such as the pHash DCT hashes which were originally conceived for videos but then adapted for images. The first rough draft of what this could look like in blockhash is done in https://github.com/commonsmachinery/blockhash/pull/12
That version is dirt simple in that it only picks four key frames from the video (one at the beginning, one at the end, and two at defined points in between), does a standard 64-bit blockhash of those videos and the concatenates them together to a 256 bit hash. I haven't done the cross-compare yet to evaluate accuracy or false positives/negatives, but it seems to work, and any alternative to this will surely only be an improvement. So that will be the "baseline" comparison :)
Problems encountered so far with videos include:
That said, it's not obnoxiously slow to step through videos, but of course, it depends heavily on the length of the video itself and the processing power available. But we're talking about seconds, rather than milliseconds.