Im delighted to hear you are planning a knowledgebase, because these
encoding issues get complex and theres plenty to say on the subject. I
reckon on average I spend at least a few hours every week talking
about various encoding issues, usually in response to specific questions. 

Ive never tried to summarize everything thats been said about mpeg4
encoding here, its not a small task, but if theres anything of use in
psat messages of mine, you are welcome to reuse anything Ive written.

In repsonse to specific questions youve asked or others have
subsequently raised:

Yes quicktime is just a container format. Most of the quicktime .mov
files used today are also mpeg 4. The advantages of not wrapping mpeg4
up as a mov are so that it can be playted without conversion by a
wider range of software and hardware.

The downsides include some servers not setup to handle mpeg4 mimetype,
some users computers not setup to have an app associated with .mp4
files, and .mp4 files currently dont support metadata, wheras .movs
have metadata capabilities. Also the fact that 3ivx only seems to want
to export its mpeg4 to .mov files (at least on the mac anyways).

For a time many believed that .mp4 files also lacked the fast start
option, which is an important thing, but I believe it turned out not
to be true, though I forget how the confusion started in the first
place, or what settings are needed.

So anyway if you are already experienced with encoding to mpeg4 .movs,
 most of the 'science' behind the settings is identical. Bitrate,
framerate, keyframe, audio settings and considerations should be the
same. (unless you are targetting specific hardware devices that can
play mpeg4, but only up to certain resolutions, bitrates, or profiles.
Eg some devices may only support mpeg4 basic rather than improved, but
until the hardware mp4 video market becomes clearer I wouldnt start
worrying about this too much yet) 

What may vary is where the options are and exactly ho they are
labelled. Also beware that because many people use mpeg4 .movs, if you
ask for advice about mpeg4 you might get people giving you settings
that only show up when saving movs. 

Also if you already have video encoded as mpeg4 .mov's, it is possible
to convert them to .mp4 files without having the reencode at all! This
is potentially very important or useful to some people, so I will make
a seperate message about this later.

Regarding your audio, it all seems a bit odd to me. I listened to both
of your clips, and the biggest difference appears to be the volume of
the audio. I wouldnt expect the extreme difference in volume to be due
to bitrate, unless something is malfunctioning. Maybe its to do with
mono/stereo options. Is most of the audio on one channel rather than
the other? Is it possible you changed any other audio setting for the
2nd version? Or maybe for some reason it is bitrate, but it shouldnt
be as far as my brain knows. Audio with too low a bitrate should
suffer from loss of detail and artefacts, just like video at too low a
bitrate. But video isnt less bright with a lower bitrate, and thats
the video equivalent to low volume?

I prefer higher quality audio settings than many videobloggers use, in
terms of Khz, but people vary greatly in how much fo the filesize they
are prepared to accept being taken up by audio. The key is to match
Khz and mono/stereo to an appropriate bitrate, just as with video the
resolution and framerate will set boundaries on what a sensible
bitrate to use is. I could say a lot more about this, but I wont right
now as this emails getting too long already.

If I have time, I would like to try to rewrite all of my encoding
thoughts into a structured resource, and you and anybody else are
welcome to reuse it.  As I dont understand what Im saying myself on
these issues sometimes, Im desperate to find ways to simplify this. If
a newcomer to videoblogging is met with replies like mine in response
to realtively straightforward questions, its a barrier to
videoblogging. The existing guides that people have done are very
cool, and Ive no doubt they have saved many may humans, many many
hours of messing around. 

But Im never satisfied, I see that quite a few issues to do with
encoding are more about personal preference, than technical
limitations. So there needs to be choice, theres so many factors that
there is not one answer to the encoding quesstion. I therefore like
the idea of creating a variety of different encoding 'profiles',
collections of settings to suit different needs. 

eg if the popular 320x240 15fps 600kbits/sec mpeg 4 settings had a
name, it would be easy to refer to them quickly, and it would also
show that they are one great option, not the only great option. Then
there would be a profile for people who want extra-small filesizes,
one for quality junkies, a few different HDV ones. 

Anyway Ive said more than enough for now.

Steve of Elbows

--- In, JD Lasica <[EMAIL PROTECTED]> wrote:
> Today I spent a little while experimenting with MPEG-4 settings.
> Because some people prefer MPEG4 to QuickTime, I've been hoping to do
> more of my video in mp4, but I've never been pleased with the default
> settings.
> So, I thought I'd ask the wise people on this list for some advice or
> pointers for MPEG-4 compression settings for publishing a video for
> display on Ourmedia. (And, yes, I know all about Michael Verdi's PDF
> primer on Video compression with 3iv ...

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