how to find duplicated frames

[fabweb]

I have an ADVC 300 which, in case of dropped frames, keeps sync by duplicating that last image in place of the dropped frame.

I appreciate this, but still would like to have a chance to try and redo this scene and see if a different player plays it better.

My question: How can I find duplicted frames in my DV-AVI? By going through it frame by frame, YES, but what would be an automated way to find those scenes that I should try to capture again?

[JohnnyMalaria]

I can think of a way - I just don't know if it exists!

If I were to write a program to do it I would do the following:

Read the first video DIF of the current frame. (A DIF is 80 bytes and a video DIF contains the compressed data for approx. 4 8x8 pixels.)

Read the first video DIF for the next frame.

Compare the two. No need to decompress the video or anything like that. Just a simple byte-for-byte comparison.

If they are identical, test the second video DIF and so on. If all the DIFs for the entire frame agree for both frames, then you have identical video information.

If they don't agree, just move to the next frame.

Repeat for the whole video file.

Since you are interested in two identical frames next to each other, it would be very quick, too.

I wouldn't be surprised if there already exists an file comparison utility that can search for strings etc that could be persuaded to do the job.

The above approach would be extremely fast.

With existing tools, I expect that Avisynth could be persuaded to do something but it would be slower.

[bobkart]

I have written a few video processing application but they only work on uncompressed (RGB) video (for simplicity).

I could write an application to do such duplicate frame detection in under an hour. It could report which initial frames (by frame number) are followed by duplicates.

Of course you would have to first convert your video to uncompressed format first. The obvious downsides there are huge file size and a fair bit of time just reading it as a result of its huge size.

[manono]

Hi-

AviSynth's MultiDecimate filter can find them by running a fast first pass. It'll output a .txt file which you'll still have to go over manually, to spot the frames with little or no differences from the previous. Then it can be set up to remove them in the second pass. Maybe it can be adapted to report only the frame numbers of those frames followed by dupes. I don't know, as that's not exactly what it was designed for. But it might make bobkart's job easier if he decides to take on the challenge:

http://www.neuron2.net/multidecimate/multidecimate.html