[theora] More examples?

[xiphmont at xiph.org]

On Mon, Feb 25, 2008 at 7:31 AM, Manuel Dahmen <manuel.dahmen at gmail.com> wrote:
> Hello,
>
>  I want to make a program to extract frame from a theora movie as
>  images. I tried with the decoding example located at theora web site
>  (dump_video.c. I use it to extract a frame as yuv image but when I try
>  to convert it to ppm with yuvtoppm program i obtain a strange image
>  ( see http://poux.be/tmp/file.ppm ). I think it's a problem with the
>   byte order for yuv, but don't I don't know anything about this format.

There are multiple problems here-- it looks like the conversion
routine is expecting way more bytes than it's getting.

>  What is the yuv format issued from dump_video.c (444, 422, 420 ?)

Whatever the Theora vide is in.  Currently, this will almost always be
420, but it could be any of 444, 422 or 420.

>  and
>  when can I find a not-too-hard-to-understand explanation of this format?

One plane of Y in raster order, left-to-right, top-to-bottom, then two
planes (U and V) in the same order but 1/4 the total size of Y.

Monty