[theora-dev] Legalese. What is stride?

Philip Jägenstedt philipj at telia.com
Mon Jul 7 15:46:58 PDT 2003

Hello all.

I've been playing around with theora since it first entered CVS, and I
like what I'm seeing. Today I've been fixing xine's theoraplugin to
understand theora_info.frame_{width,height} and
theora_info.offset_{x,y}. I only got it working after some experimenting
and basically copying the code from player_example. A few questions
related to this:

1. What are the legal requirement in regard to copying code from your
BSD-style license to xine, which is under the GPL. It would seem that
the original author made no mention that he had used code from
player_example (which it is obvious he had), so I'd like for everything
to be in order. Is it enough if there is a comment beside the relevant
code, or perhaps in the header section of the source file?

2. Getting said plugin to work was basically possible only because I'm
good at using emacs copying functions, using your code for
clipping+offset. I couldn't really understand why it worked, because
there was one relevant concept which I simply can't understand --
stride. There's y_stride and uv_stride. Everything works now, but I'd
rather understand _why_ it works, so if someone could explain what
stride is (from a little googling it seems to be a concept which exists
in most YUV codecs), I'd be very greatful.

Other stuff: I was talking to meu on #theora about the aspect values. I
wanted to add support to encoder_example to set these values, and he
voluntered to do it for me (because I could easily make a mess of it).
We agreed that the two values probably indicated pixel ratio, not the
aspect ratio for the whole image, but it doesn't appear to be clearly
defined in any docs yet that this is the case. Hence, I file a RFD
(request for documentation) in the general direction of the theora
developers, to include this in the spec. When it's clearly defined what
they are supposed to do, I will attempt to add support for it to the
xine plugin.

That is all, thank you for doing cool stuff.
  // Philip Jägenstedt
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