Lossless 29.97p to 23.976p?

[DoctorM]

Since mpeg2 can be cut, joined and NLE'ed, is it theoretically possible to take 29.97 progressive video (with a pattern of 4 unique/1 duplicate in every five) and convert it to 23.976 progressive without re-encoding?

It sounds plausible, but I've never heard of software that would allow you to apply decimation directly to mpeg without re-encoding.

Any ideas?
(I would have posted this under the editing section, but frankly, I don't think it fits any of those categories which include avi intermediate steps.)

[neuron2]

If it is soft pulldown, then yes, you can remove it losslessly.

[DoctorM]

No, I'm talking about progressive frames ABCDD.
Doesn't soft pulldown suggest interlaced playback?

[neuron2]

The converse of my statement is: If it is NOT soft pulldown then you cannot remove frames from the stream without re-encoding.

You can run a decimate filter during playback.

[DoctorM]

Sure, AFAIK there is no tool currently capable of it, but it should in theory be possible.
If you were ambitiously crazy, you could take a program like Womble Mpeg Wizard and manually cut every duplicate frame. Which suggests there's no reason something couldn't be created to do it manually.

I'm just thinking out loud at this point...

[neuron2]

With all due respect, you're just demonstrating your ignorance of MPEG2. How do you think Womble achieves what it does? Yes, by re-encoding.

[DoctorM]

But not by fully re-encoding the entire stream. It will copy almost all the original video if no changes beyond straight cuts and joins are made.
IIRC it manages this by making a small encode at the cut/join points, but that's tiny, imperceptible and negligible compared to fully re-encoding video (which Womble absolutely blows at, having the worst mpeg2 encoder ever written).

It is not the only software that (NEARLY) losslessly allows cutting and joining of mpeg2.
I didn't think you'd quibble over minutiae since most of that software manages it without a true mpeg encoder even involved.

[FlimsyFeet]

I'm pretty sure you are right in how Womble works, if you make a cut or a join, then the only bit of the video that is reeoncded is that either side of the edit point until the next I frame is reached. But, if you are making a cut every 5 frames, then you will end up reencoding the whole thing!

[manono]

That's right. Womble and all the Smart Renderers that can do frame accurate cutting have to reencode in between the I-Frames. And since you'll be making several cuts inside each I-Frame of the entire video, you'll have a much easier time just reencoding the entire thing, leaving Womble out of the equation entirely. Give it up, DoctorM, you're beating a dead horse here.

[neuron2]

I didn't think you'd quibble over minutiaeYou seem to be forgetting that your title asked for lossless removal, and your first post stated "without re-encoding". Answering your specific question is not quibbling.

Womble re-encodes GOPs around the cut point. If you remove every 5th frame, you'll be re-encoding every GOP, which is equivalent to re-encoding the entire stream.

[DoctorM]

Ok, got it. I tend to consider Womble and the like lossless, but you are correct it would be equivalent to a full recode.

[blutach]

Womble is great if you are only doing one or 2 cuts. But removing every 5th frame will, as you have now been explained, perforce require a full re-encode.

Regards