[vlc-devel] why vlc change my picture size??

David Flynn davidf+nntp at woaf.net
Thu Mar 26 18:42:03 CET 2009

On 2009-03-24, JUN LIN <lang83115 at gmail.com> wrote:
> I spend some time plugin a new v4l2 module into vlc which will capture media
> data from a Video capture card.
> on one screen:vlc will change the size of the picture which i capture from
> the PCI card
> (for instance, the original size is 352x288 but vlc will change into
> 384x288), i don't want to change my picture size really.

The format you are viewing is called CIF (it is half the height and
width of 576line SD).  SD video formats do not use square pixels (if
you look were to measure the pixels on your old SD television, you would
find that they are not square).  Your computer monitor (and HDTV) uses
square pixels, in order for the image to look correct, it is necessary
to resample the image.

As to how to fix, it depends what you are doing.
  --aspect-ratio 11:9 will fix it for local display

If you are streaming, you'll need to use the canvas module (or check if
the v4l module allows you to set the aspect ratio)

Note, if this is capture from off air television, or a TV camera, the
pictures will not be correct unless the conversion is applied.


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