NTSCFilm 23.976 versus NTSC 29.97 VCD Picture Quality?

[TheOne2424]

Would I theoretically get better picture quality if I encoded my MPG VCDs at 23.976FPS versus 29.97FPS based on this simple math:

1150bits/29.97FPS=38.37bits/frame
versus
1150bits/23.976FPS=47.96bits/frame

Wouldn't the higher bit rate per frame offered by NTSCFilm give me a better quality picture in additon to a smaller file size because of the lower frame rate? Also, would there be any audio sync problems if the source was originally 29.97? Thanks for any input.

<font size=-1>[ This Message was edited by: TheOne2424 on 2001-10-21 18:00:47 ]</font>

[BlackWinterDay]

I had a similar train of though, but my plan was to jack up the maximum variable bit rate of my xVCD's so as to obtain even better quality due to the smaller file size created by fewer frames per second... My problem is that I am capturing in MPEG-1 with ATI's MMC and I cannot seem to convert the video in TMPGEnc to 23.97 without screwing it up. Any help would be appreciated

[Kdiddy]

My train of thought is the same and I do all my DVD rips this way...as most are NTSCfilm..and I do not get any sync problems..Ive never tested to see if the file size was smaller than 29.97 or not...I think, not 100%, should not get any sync probs as long as you enocde at the same rate that you decoded the vob...so if you do DVD2AVI forcefilm 23.97, & encode that way, you are fine, because you audio gets decoded at the same rate...same with 29.97 to 29.97..think the prob comes in if you do 29.97 to 23.97 ro vice versa is where you get sync probs I think.

[vitualis]

To answer your question TheOne, NTSC-FILM VCDs (23.976 fps) look MUCH better than an NTSC (29.97 fps) or PAL (25 fps) VCDs, even from the same source.

As you've worked out, with NTSC-FILM, you are essentially getting an additional 25% boost to your bitrate for free. This makes an enormous difference.

The file size will not be smaller for NTSC-FILM though (the overall bitrate is the same and the length of the movie is the same).

Regards.

[Anonymous65]

There are some problems using 24 frames when the source is 30 frames: the mpeg software compressor needs to spend a lot of extra time converting the frame rate, and you might get motion artifacts since there are 6 frames missing from the video every second.

[vitualis]

True.

However, most DVDs (NTSC) are inherently in FILM framerates anyway...

Regards.

[snowmoon]

Using NTSC-FILM from film sources will create a better output. There are 2 resons why.

1) More bits/frame ( already covered )

2) Motion promlems with 29.97. With source that is nativly ( or IVTC'ed to film speed ) ntsc film rate converting it to 29.97 can be done in one of seval ways.

2a) Combine fileds. This will just merge the two fields together leading to a bland soft picture that breaks down most during movement. These can easly be spotted by single stepping through actions scenes. 2 blurry 3 clear 2 blurry 3 clear.

2b) Drop field or de-interlace. This will leave 6 almost duplicate frames per second in the video. This leads to a slightly jerky effect during action or panning. Easly spotted by single stepping. 4 ok frame, 1 duplicate,...

Using the right framerate is very important for good looking output. NTSC-FILM rate source can also be converted to 25 PAL without to much hassle using the AssumeFPS(25,sunc_audio=true) function in avisynth.

Good luck.