bit rate vs resolution vs fps

[wc]

I remember a while back there was a formula relating bit rate with fps with resolution. Can any tell me what that is? Thanks.

- wei

[RadicalEd]

well :\ you can find the bitrate of uncompressed video using resolution and framerate, and lossless video through approximations, but lossy video's bitrate is framerate and res independent (well, save for quality/constant quant modes, but those aren't really predictable). Anyway
Pixels width * pixels height * bits per pixel * framerate / 1024 bits in a kilobit should do it for uncompressed
i.e. 640 * 480 * 24 (rgb) * 23.976 / 1024 = 172,627 kbps

Lossless depends on the approximate efficiency of the compression algo. For instance huffman compression is usually allotted about 33%. This way we would use
Pixels width * pixels height * bits per pixel * compression reduction % * framerate / 1024
i.e. 640 * 480 * 16 (yuy2) * 0.66 (66% of the uncompressed size) * 23.976 / 1024 = 75,956 kbps

that last one would be about equivalent to huffyuv

[wc]

Thanks for the reply, but I guess I asked the question poorly. There was a formula gives a suggested min bitrate for a given output resolution and fps. I was wondering what that formula was.

- wei

[r6d2]

Sorry if I do not get your point, but why FitCD will not do here?

FitCD will calculate BR independently of resolution, but if then you fix the compression you want, you may move the BR slider to match it on any resolution.

I know it's not "the formula", but it works.

[RadicalEd]

Originally posted by wc
Thanks for the reply, but I guess I asked the question poorly. There was a formula gives a suggested min bitrate for a given output resolution and fps. I was wondering what that formula was.

- wei

Bits per pixel, the reccommended minimum (going by GKnot) is about 0.2. That way you could calculate W * H * fps * 0.2 / 1024.
Though 0.2 seems kinda high :| 1.5 mbps for 640x480 23.976fps

[scharfis_brain]

There was a formula gives a suggested min bitrate for a given output resolution and fps.

IMO there is NO formula for all circumstances, because the bitrate depends extremely on the motion, cripsness, noise and other things.

I have some movies encoded 560kbps (SBC) @ 720x304 / 25fps with very good quality

while others needed about 1200kbps with only 640x272 for good quality!

[r6d2]

Originally posted by scharfis_brain
[B]IMO there is NO formula for all circumstances, because the bitrate depends extremely on the motion, cripsness, noise and other things.

Agree with that, but I guess that theoretically at least there should be something, like for instance if you use a lossless codec, it would give you a maximum average BR. Does it make sense?