Confusion about (soft) 3:2 pulldown and extra frames

[SDeC]

I thought I understood the process, but I am confused and frustrated that my new M2V streams contain extra frames.

To illustrate, I have an uncompressed AVI comprising 217 progressive frames for 23.976 playback.

Using either MainConcept, TMPGEnc, or Vegas (with its modified MC plugin), I can NEVER encode 217 frames with 3:2 pulldown for NTSC DVD.

What I get is an MPEG with about 240 frames (give or take a few depending on the encoder). In all three cases, GSpot reports both IL and 3:2. Huh? The encoders were not configured to construct extra frames--only to add the 3:2 flag. I thought the whole point of using a 3:2 pulldown flag (which I think is called 'soft telecine') is to avoid encoding the interlaced frames.

Thus, how does one properly encode a 24fps film sequence for 29.97i DVD so that the player (and not the media) handles the rate adjustment?

I'm stumped

[manono]

Hi-

Thus, how does one properly encode a 24fps film sequence for 29.97i DVD so that the player (and not the media) handles the rate adjustment?

I have no idea how you're getting your video into those encoders, and since I use none of them, I can't help much with the specifics. However, to answer your question, you encode for progressive 23.976fps with 2:3 (or 3:2) pulldown applied by the encoder or applied afterwards by an outside program (such as DGPulldown).

You can check if it was encoded properly and had the TFF/RFF flags applied correctly by opening the resulting M2V or VOBs (if it's been authored already) in DGIndex and running the Preview (File->Preview). If the Information screen says Video Type=Film and Frame Type=Progressive, then you're OK. I think you probably are OK.

And GSpot is correct in saying you have both 3:2 pulldown and interlaced video because you do. With 3:2 pulldown applied, the output is interlaced 29.97fps (or, more properly, 59.94 fields per second). It should also say Pics/s=23.976, Frames/s=29.97 and Fields/sec=59.94.

[guns1inger]

Are you encoding at 24 fps or 23.976 fps ?

Have you tried encoding at 23.976 fps without adding pulldown, just to see how many frames you get ?

You can always add pulldown after the fact with DGPulldown.

[jagabo]

In TMPGEnc Plus set Encode Mode to "3:2 pulldown when playback" and Frame rate to "23.976 fps (internaly 29.97 fps)". This will create a file with progressive frames at 23.976 fps and 3:2 pulldown flags. The flags tell the DVD player how to create 59.94 fields per second from the 23.976 frames persecond for display on standard definition TV. Gspot will show 23.976 pics per second, 29.97 frames per second, 59.94 fields per second, 3:2 pulldown, and interlaced.

[SDeC]

Well, jagabo's post only reinforces that I knew what I was doing in the first place - thanks

I think what is happening is that most playback and review applications (such as VirtualDub) are telling me how many frames would be rendered during playback. I suppose that is sensible; but it is confusing as heck if you are literally inclined.

[jagabo]

Well, jagabo's post only reinforces that I knew what I was doing in the first place - thanks :)

I think what is happening is that most playback and review applications (such as VirtualDub) are telling me how many frames would be rendered during playback. I suppose that is sensible; but it is confusing as heck if you are literally inclined.

Yes, current versions of VirtualDub (the MPEG plugin, actually) performs the pulldown to create 29.97 fps frames (you'll see interlace comb artifacts). The reasoning behind this is that pulldown doesn't always use the standard 3:2 or 2:3 pattern. The way flags are used the picture rate can be anywhere from 19.98 to 29.97 on a GOP by GOP basis -- ie, the picture rate isn't necessarily constant in an MPEG file. But the frame rate after pulldown is always 29.97 fps and 59.94 fields per second on an interlaced TV. If VirtualDub decoded the frames without performing the pulldown you would be risking A/V sync problems. VirtualDubMod doesn't perform the pulldown; you won't see comb artifacts but you may lose A/V sync.

[manono]

I think what is happening is that most playback and review applications (such as VirtualDub) are telling me how many frames would be rendered during playback.

Not if the figures you gave are to believed. That's what I thought at first, too, until I did the math. That's why I didn't address that part of the question as I didn't want to guess. Either your figures are wrong and the 29.97fps frame count is being reported, or something else is at work:

217 x (29.97/23.976) = 271.25 (and not 240 as you said, or anywhere close to it). Maybe it was a typo and you meant to write 270.

[jagabo]

Use DGIndex to get the number of pictures (before pulldown, "Coded #") and frames (after pulldown, "Playback #") in your MPEG files.

[SDeC]

@manono

Thank you for the DGIndex reference. The numbers are good:

Coded # 216
Playback # 269

And I just re-checked the M2V through VirtualDub-MPEG2 again--but on a different machine--and now it is reporting 270 frames. Strange. I am confident that those ~240 numbers were genuine. The problem might have been a settings, codec or DLL issue (for example, I had three variants of VirtualDub sharing the same folder).

Nonetheless, I can be confident that the encode was correct (and precise). Thanks to everyone for responding and bouncing ideas.