[MPlayer-users] MENCODER: AuDIO OF SYNC when recording from TV

[Andre Bruce]

Thnx a lot for your help, you should write an article or something with
all those info .. It would probrably be usefull to other people :)

Andre

On Thu, 2003-08-07 at 20:25, D Richard Felker III wrote:
> [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> On Thu, Aug 07, 2003 at 03:01:24PM -0300, Andre Bruce wrote:
> > [Automatic answer: RTFM (read DOCS, FAQ), also read DOCS/bugreports.html]
> > i forgot to ask an other thing.
> > What are the ideal fps ?!? why 25? How many fps does a normal TV have
> > ?:P
> 
> PAL (European) TV is 25 fps. NTSC (US, Japan, etc.) is 29.97. You MUST
> record at the actual framerate or you'll get horrible bogus choppy
> video. There's no way to resample video in time (because there are too
> few samples to begin with) so if you try to record at a different
> framerate, you'll throw away or duplicate images.
> 
> This problem is greatly amplified by the fact that TV is not frames,
> but *fields*. A field is half a frame, either the even lines, or the
> odd lines, shown alternately so you have an illusion of smoother
> motion without using too much bandwidth on the air. So you really have
> 50 fields per second with PAL, or 59.94 fields per second with NTSC.
> 
> When you capture, you get 2 fields at a time, combined as one frame,
> but they're actually images from 1/50 or 1/59.94 second apart, so
> you'll see an effect known as "combing". This looks rather ugly when
> played on a non-interlaced display device such as a computer monitor
> or projection screen.
> 
> How do you deal with it?
> 
> First point: when dealing with interlaced video, whatever you do, DO
> NOT SCALE IT VERTICALLY. If you do, it will be permenantly ruined and
> there's no way you will get a clean picture out of it ever again! :(
> 
> Unfortunately there is no "correct" ideal way, but you can just record
> the video as-is (interlaced) and play it back on an interlaced display
> device, or with deinterlacing.
> 
> MPlayer can deinterlace in several ways (see -pphelp), but all of
> these essentially throw away half the framerate and lose lots of
> information. With MPlayer G2, you can use the "tfields" filter to
> deinterlace to 50 (or 59.94 with NTSC) fps, giving quite nice output,
> if your system is fast enough.
> 
> On the other hand, if you're watching a movie on PAL tv, it's probably
> not interlaced at all. That's because film is recorded at 24 fps, then
> sped up slightly to 25 fps for PAL tv. So, pairs of fields come from
> the same original frames in the movie, rather than distinct points in
> time.
> 
> For NTSC, dealing with movies gets more complicated. I won't bother
> explaining here since it sounds like you're in a PAL region, but if
> you care to learn about it, browse the archives for info about
> "telecine" or "pulldown".
> 
> > What about the bitrate?
> 
> Analog video has no such thing as bitrate. IMO you should not use
> bitrate when recording live from TV capture, but instead use vqscale=2
> for constant (near-max) quality, then figure out an appropriate
> bitrate later and do 2pass encoding with mencoder to make a copy at
> the desired quality for archival purposes.
> 
> Rich
> 
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