Convert 30fps to 24fps skipping every 5th frame?

[DragonQ]

Hi,

I have a 30fps 720p MKV video with the following frame order:

ABCDDABCDD...

Obviously it's been converted from 24fps and would be better in that original format (ABCDABCD...).

I've tried remuxing to M2TS and importing into Sony Vegas Pro 10 but if I convert to 24fps without a resample, it always gives me ABDDABDD..., which is useless. Moving the video 1 or 2 frames forward on the timeline before rendering makes no difference to the frames it uses and I can't see any options for it.

Is there any other software that'll let me do this? It'd be great to do it losslessly but I doubt that's possible so a re-encode is fine.

[jagabo]

AviSynth:

TDecimate() will adapt to changing patterns

SelectEvery(5,0,1,2,3) for every 5 frames, keep frames 0, 1, 2, 3, discard frame 4

It can't be done losslessly.

[Gavino]

SelectEvery(5,0,1,2,3) for every 5 frames, keep frames 0, 1, 2, 3, discard frame 4

ChangeFPS(24) will also produce the same result (assuming 30fps input).

[jagabo]

SelectEvery(5,0,1,2,3) for every 5 frames, keep frames 0, 1, 2, 3, discard frame 4

ChangeFPS(24) will also produce the same result (assuming 30fps input).

Yeah, but you're relying on a quirk of the math. With SelectEvery() you specify which frames to keep and which frames to lose.

[DragonQ]

What I actually did in the end was try a couple of the other encoders I have and TMPGEnc Xpress 4 worked perfectly when I set it to encode using AVC at 23.976 fps. Presumably it was pure luck that it chose to throw out the correct frames but at least it works.

Thanks jagabo though, that looks simple enough and I'll try that next time.

[jagabo]

VirtualDub's frame rate conversion will decimate too. It's just a matter of starting at the right frame (you can add or remove a few at the start).

Did you spot check your result? There are often breaks in the repeat pattern from edits, dropped frames while capturing, etc.

[DragonQ]

I spotted one repeated frame but that was at a point in the original where the frame was repeated twice. The rest is fine.

I considered VirtualDub but couldn't get it to read the file. No version I know of can read TS files and VirtualDubMod didn't like my MKV either.

[Gavino]

ChangeFPS(24) will also produce the same result (assuming 30fps input).

Yeah, but you're relying on a quirk of the math. With SelectEvery() you specify which frames to keep and which frames to lose.

Yes, SelectEvery() is more explicit.
But it can be useful to know that, when removing every Nth frame, ChangeFPS (whether by quirk or by design) always removes the last of every N, exactly what was requested here.

(Conversely, when increasing frame rate by repeating every Nth frame, it repeats the first of every N.)