On Sun, 04 Feb 2007 08:29:28 +0000, Andrew Church wrote: >>hmm... further, is the Example 6 supposed to be the standard way to convert >>between 4:3 & 16:9 videos? > > It's one example of such a method. There are many different possibilities. > >>I tried to apply the mechanism to convert a 640x480 @ 4:3 video back to >>720x DVD video, but get a 720x540 one instead of the original 720x576. >>Why the difference? Here is how I calculate: >> >>The 640x480 @ 4:3 video has 60 pixels black border on top and bottom. So I >>"use the -j option to change the size of the input video before the zoom >>is performed. ", as in Example 4. That'll give me 640x360 @ 4:3. > > Actually, it gives you 640x360 @ 16:9. -j and -Y change the frame size > without changing the PAR, so the DAR must change.
Please forgive my dense, I still don't understand it. in Example 4, after clipping with -j, the 16:9 video is still considered to be 16:9. I think that make sense, you can arbitrarily clip the video into any weird shapes (even tall), but 16:9 still hold. I.e. whatever left, will still play fine, without distortion. Now suppose this 640x480 @ 4:3 video is handed over to me by somebody else. I don't know how he come up with it, whether it was from 16:9 source, or 4:3 or 1:1, as long as it plays fine in movie players, or on TV, It is true 4:3. Otherwise, there will be distortion. >>The output frame sizes would be >> >> width = 720 >> height = (PAR * width ) / DAR = ( 1/1 * 720) / (4/3) = 540 >> >>If there is no distortion during the 2 DAR conversion, the result should >>be exactly 720x576. What's wrong here? > > Leaving aside the DAR issue, you're using the wrong PAR. As I mentioned > before (and as is also mentioned on the main "aspect ratio" page), DVDs > do not use a PAR of 1:1. what PAR should I use then, suppose this 640x480 @ 4:3 video is handed over to me by somebody else. and I don't know how he come up with it. but it plays fine. > In fact, since DVD players adjust their PAR to > match the video's frame size and DAR, there is no need to perform these > calculations at all; you just need to resize the video to the proper DVD > frame size with -Z and use the proper --export_asr code, as in Example > 2. Again, I'm lost here. What is the condition that there is no need to perform these calculations? any arbitrary video, eg 672x272 one? sorry again for my dense, as I said, the more I looked into it, the more convoluted it appears to me. -- Tong (remove underscore(s) to reply) http://xpt.sf.net/techdocs/ http://xpt.sf.net/tools/
