Frame rate vs file size

[Chengbin]

I thought if you had a lower frame rate, it means you have less frames to encode, which means a smaller file size. But I did this encoding of Family Guy that just proved to be the opposite. I used the same setting for both, and the 29.976fps encode is smaller than the 23.976! (144kbps vs 146kbps).

How is this possible? Did I misunderstand what frame rate is?

[poisondeathray]

filesize = bitrate x running time

*note fps doesn't even enter the filesize equation

think of the same bitrate as distributed over more frames with a higher fps, so each frame is of lower quality, but the motion is smoother (assuming they are not just poor dupes)

[Chengbin]

So lower fps = better quality (assuming I can't see the motion smoothing from the higher fps)?

[kemuri-_9]

framerate doesn't have anything to do with the number of frames to encode, it only represents the speed of how they appear on the screen.

i suspect you're getting decimation/inverse teleclining confused with setting the framerate here.

you should have the encoded video at the same fps as what you started with (unless you did apply some decimation/pulldown)

[poisondeathray]

The pratical example where this applies is 30i video footage; either you deinterlace it to 30p or bob it to 60p

The 60p is smooth as butter, and makes 30p look jerky in comparison. But 2x the number of frames means more bitrate is required for the same image quality per frame (not necessarily in a linear fashion)

If you are just using a normal progressive DVD or blu-ray source, none of this should apply, as kemuri says above

[Chengbin]

I'm encoding from a DVD. The fps on it is 29.976.

Is it a good idea to convert it to 23.976?

A little OT but is that the way those 120Hz HDTVs work? By converting them to 120fps, and motion becomes smoother?

I still don't really get this. If fps is just the speed the video plays back, why can't you just play it at 30 (or 60fps)? The only reason I can think of is in a 30fps video, there are 30 frames per second, and that's the speed you play it back. Also, when I used x264, the number of frames to encode in 29.976fps is 9000, but for 23.976 it was 7200.

[kemuri-_9]

I still don't really get this. If fps is just the speed the video plays back, why can't you just play it at 30 (or 60fps)? The only reason I can think of is in a 30fps video, there are 30 frames per second, and that's the speed you play it back.
if you play the video at the wrong fps rate, audio desync occurs.

Also, when I used x264, the number of frames to encode in 29.976fps is 9000, but for 23.976 it was 7200.

then you applied 1 in 5 decimation (hopefully proper inverse telecline) to drop the frame count as well.