Re: Fix for AV-sync with FFMPEGrec

[joe briggs <jbriggs@xxxxxxxxxxxx>]

Thanks - great clarification!

On Monday 31 December 2001 04:15 pm, you wrote:
> joe briggs (jbriggs@xxxxxxxxxxxx):
> > Isn't this standard conversion a hardware process?
>
>   Being able to output a composite NTSC signal, a VGA signal, or a PAL
> signal is a hardware process handled by the video card.  However,
> software still needs to provide the images to display.
>
> > For example, you have long been able to buy analog standard converters
> > from RadioShack, and you have certainly been able to purchase digital
> > standard convertser which frame grab in one standard, and clock out in
> > another - these are used by tv stations and tape conversion houses.
>
>   There are many poor methods of framerate conversion.  See my repost
> where I describe one way of using 50-50 image blurring to deal with
> motion.  Other converters screw motion.  I see some really strange
> artifacts sometimes when watching PAL-recorded material broadcast here,
> and often the motion is just messed up.
>
>   Do a search on 'pal ntsc conversion' for more discussion.  There's
> also a really great article on it that I found once and I'll try to find
> again...
>
> > However, many "book pc's" - these small footprint PC's, usually a i810
> > chipset, have both VGA and composite/s-video output as well.  In the
> > bios setting for these, you have the option of selecting the TV video
> > mode to PAL/NTSC/SECAM.  Even if you are running Linux and set X to
> > 640x480, it looks great on the TV out.
>
>   Watching low-framerate material, like using your desktop or watching a
> 24fps video, looks fine on displays at 50hz (PAL TV), 59.94hz (NTSC TV),
> and a VGA monitor (50hz+).
>
>   Watching 25fps or 29.97fps material on an NTSC TV is also pretty safe,
> you'll likely only see a stutter every 30 seconds or so depending on how
> different your clocks are.
>
>   But watching true 50fps or 59.94fps material on any of these displays,
> you start to get into trouble.
>
>   Remember, when you watch a PAL TV, you're watching 50 images per
> second, and with NTSC TVs, it's 59.94 images per second.  Recording at
> half rate like 25fps or 29.97fps you're already protecting yourself
> against framerate judder.