DVD-RB + CCE Basic Inverse-pulldown question

[himadriatt]

(a) The SOURCE DVD has VOB files with 29.970fps.
(b) The ENCODE PHASE produces M2V files with 23.976fps...courtsey CCE Basic?
(c) The REBUILD PHASE produces VOB files with 29.970fps.
(d) Frame by frame advance of (b) and (c) using DGIndex (F6 Play with Single Frame advance) seems to be identical.

Question: I thought DVD-RB again performing a 3:2 pulldown on (b) to produce (c). What explains my observation (d)? Is the playback length affected in anyway?

I am also curious if a DVD is still valid & playable if the VOB's had 23.976fps? I mean can we save on space that way?

[SpazzHH]

All NTSC discs are processed by DVD-RB at 23.976fps, to allow for the proper processing of hybrid(telecined) sources. They are then returned to there original frame rate during Rebuild so that the playback length is correct.

It would not be possible to leave them at 23.976, as they would not be DVD compliant. NTSC discs must be at 29.97. The file size on progressive material is not really affected as the frame rate conversion is usually done with flags that the player reads, not with the actual insertion of extra frames.

I'm sure there is more that other members could add to this, but it seemed like the easiest explanation.

[himadriatt]

Thanks SpazzHH for your info with DVD-RB behavior.

...The file size on progressive material is not really affected as the frame rate conversion is usually done with flags that the player reads, not with the actual insertion of extra frames...
Hmm...I did not know this. That seems to explains the equality of total frame count in the M2Vs from (b) and the VOBs from (c). So, how is this frame rate conversion done during playback. Does it mean the Player is introducing frames (3:2 pulldown) on the fly? Is this fps info within the MPEG2 stream? I am sure I am missing something here.

[SpazzHH]

So, how is this frame rate conversion done during playback. Does it mean the Player is introducing frames (3:2 pulldown) on the fly?

Yes.

Is this fps info within the MPEG2 stream?

Yes. Rebuilder copies the flags from the original, and inserts them back into the same place in the re-encoded stream. The use of flags is the most commonly used practice since the bitrate can be allotted to a fewer number of frames, increasing quality, and since most NTSC film cameras shoot at 23.976 in the first place.

[himadriatt]

Thanks SpazzHH. I see now...the use of flag is pretty efficient then. It never occurred to me thus far since I had been literally interpreting the 29.970fps in VOBs. Is there a lookup tool to show "true fps" encoded plus the "flag info" for any given VOB?

[wmansir]

You can use DGIndex on the original .VOB. Hit F5 and it will preview the file and tell you the video type (FILM= 23.976fps with pulldown flags, NTSC = really 29.97fps video) as it goes. It may just say FILM or NTSC that means it 100%, if it's mixed it will say 90% FILM etc. It can take a while though. If you want to do the whole file you can save a project file, open it in a text editor and check the last line of the file.

Also, ignore the FRAME RATE info, it is based on the program settings not the video flags.

[himadriatt]

Thanks wmansir. Based on your post, I now see/interpret better with DGIndex...that answers my question.