[MEncoder-users] capture: synchronization problems

[Kyle Schmitt]

--- Oded Shimon <ods15 at ods15.dyndns.org> wrote:
> On Wed, Mar 23, 2005 at 11:28:22AM +0100, amber
> wrote:
> > > Plus, if you are going to re-encode to MPEG2/4
> later, it's better to stick with a
> > > codec in the same family.
> IMO, I really don't agree with this. You should
> capture using some kind of 
I have to agree with you there.  A high bitrate lossy
codec doesn't loose very much, and rarely produces
artifacts (thats why they use one for things like
laserdisc and dvd etc).  I would use a lossless codec,
but even when I have the space, it frequently over
runs my disc bandwidth and then the whole capture
process goes to hell.

As far as the keyint issue is concerned, the default
keyint is absolutely fine for video capture.  I havn't
had any issues editing those files either, but perhaps
thats due to my way of editing which isn't very
efficient.

> > i understand mjpeg causes some artifacts.
> I've never seen such artifacts. I could be wrong
> though. Could someone tell me 
> exactly what artifacts? MJPEG by definiton is lossy,
> but for all my capturing 
> needs I found it very high quaality at small
> filesize.
Ahh here's the rub.  Although both mjpeg and mpeg1/2/4
are lossy codecs, the artifacts they produce are
different.  <oversimplification>Mpeg codecs simplify
the image into blocks that can be shifted.  The fewer
blocks it uses, and the more blocks it reuses, the
smaller the file.</oversimplification>  <gross
oversimplification>Jpeg translates the image into
math, and then saves space by simplifying the math NOT
the image.  The more the math is simplified the
smaller the file.</gross oversimplification>
  The result is if you have an artifact in an well
created mpeg1/2/4 stream, things usually look blurred.
 With Mjpeg (and of course jpegs in general) even
though there was real data loss, preceptually (what we
see) there is MORE data (think of it as an awful ugly
texture)  I've posted an image here
http://www.slackwaregallery.com/displayimage.php?pos=-1910
in tiff format to give you an idea.


		
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