[theora-dev] further debugging of my ogg/theora decoder

salsaman salsaman at gmail.com
Tue Nov 18 07:47:59 PST 2008

On Tue, Nov 18, 2008 at 7:28 AM, Ralph Giles <giles at xiph.org> wrote:

> On Tue, Nov 18, 2008 at 2:21 AM, salsaman <salsaman at gmail.com> wrote:
> > Right, that is what I would expect. I think I will write an ogg file
> checker
> > that checks all granulepos and keyframes to make sure the problem is not
> in
> > my test files. Some of the files were created with older versions of the
> > encoder. For example I have one file where I need to subtract 2 from all
> > keyframe values in order for it to decode properly.
> Hmm. Some of the alpha encoder releases recorded the frame index, not
> the frame count. Such stream declare their version to be 3.2.0 instead
> of 3.2.1 as in the current theora spec.
>  -r

Yes, I think the file

is like that (0 based keyframes).

I am seeing other oddities in the file (I think) maybe somebody can confirm
or deny this:

there is a granulepos 68516 in the file, which is (1070,1106) zero based. If
I begin decoding from that page, I get (2 pages) [68516, 68518] 1107 (?), (2
pages) [68518, 70976] 1108 (?)  (keyframe) (2 pages) 1109 (?).

However, the keyframe should be 1109 (zero based) according to later gpos.

I think what is messing me up is that there are 2 granulepos in a row with
the same value. If I start from the second page with gpos of x, then I miss
a page (because I should be starting on the first occurance of x).

Surely the second page should have granulepos of -1 ? Is this another known
issue ?

Is this something that ogg_page_packetsout() could solve ?

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