divx 23.976-convert to 29.97 or not?

[banny]

If I have a divx (avi) file that is at 23.976 fps, when converting to DVD using TMPGenc should I leave the output at 23.976 or convert it to 29.97?

It doesn't seem to make any difference to the quality either way?

thanks

[adam]

Leave it at 23.976fps but turn on the 3:2 pulldown while playback option. This will make the dvd player do a real time telecine of the movie as it plays. Basically it is encoded at 23.976fps but is played back at 29.97fps because that's what the NTSC standard requires.

The short answer is that if you have a 23.976fps source you NEVER want to convert to 29.97fps if you are creating a digital format like VCD, SVCD, or DVD. The only reason you would ever want 29.97fps footage is if you were creating an analog format like VHS or Laserdisk where there is no support for a real time telecine. If you were to do this than you would also have to use the 3:2 pulldown filter in TMPGenc's advanced options. Simply setting output to 29.97fps will cause TMPGenc to randomly repeat frames which will create a horribly choppy output which will be unwatchable.

No the quality is definitely not the same. When you telecine film (24fps) to 29.97fps you create new frames that did not exist before. These are created from the existing fields. This means that you have about %20 more frames per second and that means that your bitrate is spread out %20 more which yields a definite decrease in quality.

NTSCfilm (23.976fps) material has 20% less frames, but its not necessarily 20% more efficient. The additional frames at 29.97fps are repeated fields, so they are really redundant information. So while they will waste your bitrate it won't necessarily add up to a 20% difference. According to most authorities ntscfilm is about 15% more efficient than NTSC, and thus at the same bitrate should be 15% higher quality.

[banny]

that clears that one up

thanks adam