Why fps and frame size are not affecting my file size?

[hillel@kaltura]

I am exporting from After with Media Encoder a composition. I open the export settings, and from there I choose H.264. In the basic video settings panel, no matter which frame size or frame rate I am setting, the file size is always the same. Only the bitrate has an impact on the file size.

This is very weird to. I can't understand why a video 1920x1080, 30fps has the same file size than 800x600, 24fps. Anybody has an answer?

[Mylenium]

It's probably simply a bug in the estimation code. in any case, it's just a prediction, not the real file size. You won't know how large the files actualyl are until you render them.

Mylenium

[hillel@kaltura]

The actual file also remain the same.

[Dave_LaRonde]

You're using the same bit rate.  Change it and the file size changes.

[hillel@kaltura]

Why is that? I just don't understand. How come only the bitrate change the file size?

[Rick Gerard · Accepted solution]

If you have the same data rate set for both frame sizes then the smaller frame size and lower frame rate will have less compression than the larger clip so the file sizes will be close to the same size. Multiply the data rate by the length of the clip and you get the approximate file size. A 4K file will be highly compressed at a data rate of 25 mb/sec but an SD (720) clip at the same data rate will have much better edge and chroma detail because it is far less compressed. Both will be very close to the same size.

You should spend some time learning how MPEG compression works. Take a look at the YouTube or Vimeo compression recommendations and check out the different recommended data rates for the different frame sizes. That should help you understand the problem.

[BIGMAMA]

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