What is pull down?

[indiannawaf]

I generally use HCEnc for my conversions. Whenever i load an avisynth script HCEnc gives a message that it is recommended i check the pull down checkbox.
I never really did Check it. It also does not have any mention on this forum.Checked the HCEnc guide too. Just couple of days ago i read comments on the latest HCEnc 0.20 that some pull down function has been fixed.

So guyz what is pull down? Should i check it or not when converting my videos?

Thanks.

[guns1inger]

Pulldown is a set of flags embedded in the mpeg stream that tell the playback device how to display the video. The most common usage is NTSC video that is encoded at 23.976 fps. Standard interlaced NTSC is displayed at 29.970 fps, however if the movie is encoded at 23.976 fps there is a problem. Pulldown flags tell the player which fields to duplicate, in what order, to produce smooth 29.970 fps playback.

However it doesn't end there. You can also use pulldown flags to fool the player into other tricks. PAL video plays back at 25 fps, with a resolution of 720 x 576. To convert it to NTSC requires changing the framerate to either 23.976, by slowing it down, or 29.970 by duplicating and blending frames. Either way, it also requires altering the length of the audio to avoid sync problems. It is a major pain in the arse, and difficult to get right. However you can solve most of these problems by resizing to 720 x 480 and encoding at the original PAL framerate of 25 fps. The video remains the same length, so audio stays in sync. You can then apply the appropriate pulldown flags to tell an NTSC player to display 29.970 fps to the TV.

Pulldown flags can be applied while encoding (CCE, ProCoder and Tmpgenc seem to do this pretty well), while authoring (DLP will add pulldown to 23.976 fps footage) or after authoring with DGPulldown - the most flexible solution of the lot.

So short answer - if you encode 23.976 material then you need pulldown. If you use HCEnc .20 you can let it apply the pulldown - it seems to work. If you have an earlier version then dont let it apply the pulldown, use DGPulldown instead.

[indiannawaf]

Thanks mate....that was clear enough. Ya i use the new HC so no problem.

[guns1inger]

Note : I said it seems to work. Test it carefully to make sure it does. If your video seems to playback strangely, use DGPulldown instead. The author of HCEnc is from PAL land (sane chap) and so some of the idiosyncrasies of NTSC are only just starting to mature.

[indiannawaf]

One more doubt though. How do you make out whether pulldown has been applied or not? For example, how did you come to know that the lower versions of HCEnc donot apply pulldown correctly?

[Alex_ander]

Pulldown flags can be applied while encoding (CCE, ProCoder and Tmpgenc seem to do this pretty well), while authoring (DLP will add pulldown to 23.976 fps footage) or *after authoring with DGPulldown* - the most flexible solution of the lot.

You must have meant 'after encoding' .
DGPulldown software will reject anything but elementary progressive MPEG2 stream (accepts neither system nor program streams, even without audio encoded), independently of file extension.

[Abond]

One more doubt though. How do you make out whether pulldown has been applied or not? For example, how did you come to know that the lower versions of HCEnc donot apply pulldown correctly?

Load the encoded mpeg video file in GSpot. Look for the frms/sec = 23.976, but pics/sec = 29.97 (or it was the opposite). As for not correctly applied - well jerkiness, audio asynch and so on can show that it was not correctly applied.

[guns1inger]

You must have meant 'after encoding' smile.gif .

Fair call.

One more doubt though. How do you make out whether pulldown has been applied or not? For example, how did you come to know that the lower versions of HCEnc donot apply pulldown correctly?

FulciLives found this when he was testing HCEnc for a guide he was working on. He found some strange behaviour when reviewing the results and followed it up with the author. The author has since made adjustments to both GOP settings for NTSC, and the Pulldown routines. FulciLives has tested again and found that these issues appear to be resolved, however it is still early days.

[indiannawaf]

Thank you masters! This site sure is a storehouse of valuable info!