[MEncoder-users] Flashvideo for YouTube using mencoder

[Nicolas George]

Le quartidi 4 ventôse, an CCXVI, Ben a écrit :
> That's actually contradictory to reality. If I reduce the number of
> keyframes, the bitrate of the video lowers, meaning quality
> requirement is lower. I don't think it improves quality, ever.

There is no contradiction, but some misunderstanding on the terms.

For a fixed quality, enlarging the maximum interval between keyframes will
reduce the average bitrate.

For a fixed average bitrate, enlarging the maximum interval between
keyframes will increase the quality.

A simple mathematical reasoning will show that is so. The purpose is to
optimize the balance between quality and bitrate. Mathematically, that means
finding, among all the possible bitstreams, the bitstream that gives the
maximum result for the function b |--> balance(bitrate(b), quality(b))
where balance and quality are function you define according to your own
taste.

Well, max is an increasing function: if A is a bigger set than B, then or
any function f, the maximum of f over A is greater than or equal to the
maximum of f over B, since the value that gives the maximum in B is also in
A.

Decreasing the maximum interval between keyframes means accepting a smaller
set of bitrates. Thus, the maximum of our function is smaller. QED.

Regards,

-- 
  Nicolas George