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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good questions. 1) legalese. I'll let someone else post a definitive answer, but the only real requirement of our license is that you give proper credit. Check out the license stuff at xiph.org. <p>2) Stride (Also sometimes called pitch) is the number of bytes (or pixels, same in most YUV cases) between one horizontal line of pixels and the next. This number *might* be equal to width -- in the simplest case, that would be so. However there are often times when it is convenient or necessary to have stride > width. An example would be when your destination memory represents physical video memory of some sort (direct screen memory or, more often these days, an 'overlay'). Say your destination memory is 512 x 512 bytes, but your image is only 320 x 240. Height is no problem (just compute an offset into the destination memory), but width cannot equal stride or the image will look like a scrambled strip of pixels. In this case, width=320 and stride=512. This is why many video API's include stride as a separate parameter -- it often reduces the need for intermediate buffers and extra copy routines. 3) aspect ratio -- that's an important issue. My assumption is that we mean the aspect ratio of the pixels as opposed to the actual frame, but this should definitely be clarified. ___ Dan Miller (++,) Founder, On2 Technologies> -----Original Message----- > From: Philip Jägenstedt [mailto:philipj@telia.com] > Sent: Monday, July 07, 2003 6:47 PM > To: theora-dev@xiph.org > Subject: [theora-dev] Legalese. What is stride? > > > 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 > --- >8 ---- > List archives: http://www.xiph.org/archives/ > Ogg project homepage: http://www.xiph.org/ogg/ > To unsubscribe from this list, send a message to > 'theora-dev-request@xiph.org' > containing only the word 'unsubscribe' in the body. No > subject is needed. > Unsubscribe messages sent to the list will be ignored/filtered. >--- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'theora-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.
hi Mau -- I personally think it is necessary or at least highly advisable. VP3 has strong codec support on multiple platforms. A transcoding path will make many tasks much easier. I think we are at least a year away from stable quicktime and (if ever) windows native codecs for Theora. Transcoding allows a way around this in the short term. Everyone at the meeting seemed to agree that adding the flag is not a problem. If anyone disagrees, please speak up now. -----Original Message----- From: Mauricio Piacentini [mailto:mauricio@tabuleiro.com] Sent: Monday, July 07, 2003 7:23 PM To: theora-dev@xiph.org Subject: Re: [theora-dev] Legalese. What is stride? <p>Hi dan. Sorry I missed the monthly meeting.> 3) aspect ratio -- that's an important issue. My assumption is that wemean the aspect ratio of the pixels as opposed to the actual frame, but this should definitely be clarified. I have added support (at Philip's request) for the encoder to accept aspect ration and frame rates from the command lines. It is in cvs. Also added support for splayer to be able to play streams with no audio, in order to help me test the transcoder draft on Windows. There is one pending issue, regarding the transcoder from VP3. I am implementing it as a separate tool, trying not to alter libtheora functions. I already did a tool to extract video frame data from .avi, and dump it with the appropriate headers etc to a theora stream. Did not work at first, of course ... :) Before I spend several days debugging the byte data compared with VP3 codecs I would like to ask a question: is this something we all agree is necessary? Are we willing to make alpha3 for this change? It will mean at least one header change (the reversed image flag.) Regards, Mauricio --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'theora-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered. --- >8 ---- List archives: http://www.xiph.org/archives/ Ogg project homepage: http://www.xiph.org/ogg/ To unsubscribe from this list, send a message to 'theora-dev-request@xiph.org' containing only the word 'unsubscribe' in the body. No subject is needed. Unsubscribe messages sent to the list will be ignored/filtered.