[MEncoder-users] Flashvideo for YouTube using mencoder

[Gilles Pelletier]

I have been reading this thread. In spite of the sometimes aggressive
language, it is quite instructive. It has forced the gods to come down
from the heights, as it were, and discuss things in a
human-understandable way and for that I am grateful. I have learned a
lot and will continue to research the links provided.
Thanks again.

On Wed, Feb 27, 2008 at 8:49 PM, Rich Felker <dalias at aerifal.cx> wrote:
> On Wed, Feb 27, 2008 at 09:22:17AM -0800, Phil Ehrens wrote:
>  > Reimar Döffinger wrote:
>  > > On Tue, Feb 26, 2008 at 09:51:09PM -0500, Rich Felker wrote:
>  > > > On Tue, Feb 26, 2008 at 10:26:09AM -0800, Phil Ehrens wrote:
>  > > > > Geez. And here I thought I was explaining why P-frame size didn't
>  > > > > matter. Oh well...
>  > > >
>  > > > Did I accidentally target my comments at the wrong person?
>  > >
>  > > I think so. But I fear he is involuntarily used to being targeted :-)
>  >
>  > I think I got into trouble when I referred to the temporal
>  > domain in general, not with reference to timestamps.
>  >
>  > What I meant was that nobody experiences the presentation of
>  > I/P frame encoded material as inherently degraded, because
>  > humans cannot distinguish between the same frame being
>  > presented twice and two frames that were recorded at different
>  > times with identical content.
>  >
>  > So there is no perceptual difference between a displayed
>  > I-frame and the null P-frame that follows. This is a
>  > wonderful result, because the average bitrate is halved
>  > without affecting image quality.
>
>  There is nothing "perceptual" about this result. It is a purely
>  mathematical result. The contents are bit-for-bit IDENTICAL.
>
>
>  > The huge potential win
>  > from dynamic GOP size follows from this.
>
>  Huh?? Now I think you really have no idea what you're talking about.
>
>  There is only one advantage to using a short keyframe interval (aka
>  keyint and very similar to the idea of "GOP size" with minor technical
>  differences): increased seeking efficiency. Most players only allow
>  you to seek to keyframes; seeking to other frames requires first
>  seeking to the prior keyframe then decoding all the reference frames
>  up to the desired frame.
>
>  [Actually there's another tiny issue, that if the encoder and decoder
>  IDCT implementations differ slightly in behavior, extremely long
>  keyint values will result in image corruption. This is only noticable
>  with extremely bad implementations or keyint values larger than 500 or
>  so, which no one uses anyway.]
>
>  Other than that, keyint should be made as large as possible. At a
>  fixed bitrate, a video with large keyint will have much higher quality
>  than one with low keying. At a fixed quality, the video with large
>  keyint will be much smaller.
>
>  FYI, regardless of keyint, encoders can choose to encode a frame as a
>  keyframe even if the whole keyint has not elapsed. This is usually
>  referred to as "scene change detection", and it serves two goals:
>  making it possible to seek to the exact point of a scene change, and
>  taking advantage of the fact that it's usually more efficient to
>  encode a completely new picture as an I frame instead of as a P frame.
>
>  Rich
>
>
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-- 
Gilles