[MPlayer-users] Re: Size of MP4 video not correctly recognized.

[Joakim Plate]

Just wanted to bump this once more. as the discussion once more came on
doom9.org. it is very possible the file is corrupt. but...

> width and height specify the track's visual presentation size as
> fixed-point 16.16 values. These
> need not be the same as the pixel dimensions of the images, which is
> documented in the sample
> description(s); all images in the sequence are scaled to this size,
> before any overall transformation of
> the track represented by the matrix. The pixel dimensions of the images
> are the default values.
> 

notice how it says scale in the above quote from the standard. it really never
ever talks about cropping the image to the given size. 

> In ISO/IEC 14496-14( MP4 File Format)you will find this:
> In MPEG-4 both visual and aural composition are done using the BIFS
> system. Therefore structures marked as “template” in the ISO Base Media
> Format which pertain to composition, including fields such as matrices,
> layers, graphics modes (and their opcolors), volumes, and balance
> values, from the MovieHeaderBox and TrackHeaderBox, are all set to their
> default values in the file format. These fields do not define visual or
> audio composition in MPEG-4; in MPEG-4, the BIFS system defines the
> composition.
> The fields width and height in the VisualSampleEntry and in the Track
> Header Box shall be set to the pixel dimensions of the visual stream.

this is where it get's ambiguous, what is really meant with visual stream? it
could be interpreted as what is to be presented to the user (or out from
decoder), wich then causes no trouble given the scaling above.

/Joakim