[MPlayer-users] How To: best way to rescale

[Rolf Ernst]

On Tue, Feb 23, 2010 at 1:51 AM, Oliver Seitz <info at vtnd.de> wrote:

>
> > The resolution is part of the container information (AVI/MP4/MATROSKA).
> > Whatever this info says, that'll play. There is no recording involved.
>
> Sorry, I thought the encoded video frames were encoded in a certain
> resolution. So, if I set the video resolution in the header to some other
> value I had feared the video wouldn't decode at all. Well, it is no
> straight video format, but yuv4mpeg e.g. has size information in the
> header only, and if this information is altered, the video can not play
> anymore.
>
> Besides, If a true video format allows to have the video some resolution
> differing from the frames, it might still not play on the limited hardware
> as frames of more than 800x600 would have to be decoded and then scaled
> down to what's given in the file header. I can't imagine the home theatre
> player is stupid enough to cheat itsself like that.
>
> Greets,
> Kiste
>

There is a native resolution inside the file. For example, I like to encode
my files all in 720x480 *it's a arbitrary number, I could choose 600*600
just as well). Then there is something in the header that says (depending on
container) that contains information about the display aspect ratio (which
translates to the rectangular shape of a pixel) and/or output size, width
and length.

Of course, it depends on the player whether that will actually be observed.
As an example: I use XBMC which has its own player. This player will observe
all these things, it actually allows you to switch between various
interpretations of this information. There are hardware players which will
not observe this information although most players that play Matroska format
are pretty compliant. Most players that play AVI files will ignore the
aspect ratio placed into it by mplayer. Mplayer itself will observe
information from Matroska.

I guess in the end it depends on what soft/hardware plays it back. Again, if
you use mplayer you can simply tell it how you want it rendered through
command line switches (or resizing the window if you can do this in you
particular application).