How to find dropped frames quickly

[Elic]

Hi all!

When I capture VHS tapes, sometimes there are dropped frames. But when I capture the same tape repeatedly, dropped frames almost never encounter in the same place. So re-capture scene with dropped frame only will be sufficient.

How can I quickly search for dropped frames in captured AVI, without comletely decoding it?

[FlimsyFeet]

Don't know if this is what you want, but if you load the AVI into VirtualDub you can press "}" (that's "shift+]") to skip straight to the next dropped frame.

[Elic]

FlimsyFeet, thank you very much! This tool is exactly what I searched for.

[mustardman]

This is certainly true for capture with analog cards, and may even apply for IEEE1394 capture cards installed directly in the PC. However, it does not apply to external DV capture devices (such as the ADVC-100). The capture application only reports frames that were not written to disk, not the frames that were dropped (or duplicated) in the capturing process.

The timing variations in VHS (tape stretch, etc) can lead to a frame rate that is too high, or too low (eg: PAL 24.999 fps instead of 25.0000 fps). IEEE1394 is not capable of dealing with this variation, so for the example given above, 1 out of every 1000 frames is going to be duplicated. Similary, 1 frame every 1000 frame will be dropped if the input is 25.001 fps. Again, I will emphasise this is not reported by the capture application.

I have seen this happen (on long captures). Capture again, and the dropped/duplicated frame moves to a new spot.

Note: Detecting drops is extremely hard (but can be done with custom written software). Detecting duplicates is relatively easy with AVIsynth, but is time consuming.

My solution is to only capture short segments (5 to 10 minutes) at a time.

MM.

[Elic]

mustardman
Thank you for suggestion. I have no DV device, just "conventional" analogue TV tuner (more precisely, it is Aver 305). But sometimes I observed totally (including noise) duplicated frames in my captures, with no dropped frames at all. Maybe this effect depends on capturing software.

> My solution is to only capture short segments (5 to 10 minutes) at a time
I agree. Moreover, for instance, it is good to make pauses during capturing of TV show on commercials. But sometimes, re-capturing is really last resort :(