[MPlayer-users] Re: slightly confused by mencoder output

[Matthias Wieser]

Am Montag, 12. September 2005 22:49 schrieb Rich Felker:
> On Mon, Sep 12, 2005 at 10:37:41PM +0200, Matthias Wieser wrote:
> > Am Montag, 12. September 2005 06:39 schrieb RC:
> > > On Sun, 11 Sep 2005 22:08:25 +0200
> > >
> > > The Eye <mhellwig at gmx.at> wrote:
> > > > video0:width=720:height=530:
> > >
> > > A height of 530 is nonsensical.
> >
> > Right.
> >
> > > Since the content is interlaced, you
> > > can only capture at the card's full heigh (576 PAL / 480 NTSC) or
> > > exactly half (or 1/4 1/8 etc).
> >
> > Or any other supported resolution if you have a saa7134 card because
> > the saa7134 chip has a not-so-bad deinterlacer.
> >
> > > > crop=688:518:16:6,pp=fd
> > >
> > > Your output dimentions should be exact multiples of 16.
> >
> > That's not so important if you don't care about the bitrate. If in
> > doubt add 10% to the bitrate if your output dimentions are not
> > multiples of 16.
>
> Are you sure? IMO you're still likely to get artifacts on the border
> blocks.

Did not see any when dimensions are multiples of at least two. But I did 
not test any uneven dimensions. Some time ago there was a comparison of 
different video dimensions on this mailinglist (or -dev-eng). IIRC the 
PSNR showed a sawtooth like curve for increasing video dimensions. Local 
maxima were at multiples of 16. 
=> Yes, it's bad not to have multiples of 16 but it's not the end of 
world.


> Also it's totally invalid to crop with a y-offset that's not a 
> multiple of 4 if you video is interlaced. You'll be exchanging the
> fields and the chroma will not line up with the luma.

Huh? Did you read my email? That's what I wrote.


> > I think it is much more important to take care that the vertical crop
> > offset is a multiple of four which is not the case in The Eye's
> > mencoder command line.
>
> Yes... most definitely. Glad you caught it too.

Glad you read my email.

> BTW can we make vf_crop fail to initialize with bad y-offset unless
> you pass a force option to it..?

Would be very nice. Maybe some printf's for bad video dimensions, too.

Matthias