Hi, A while ago, I asked about resizing and aspect ratio here in this mlist, and thanks Andrew for writing up the following Wiki for me to understand the topic:
Calculating Frame Size And Aspect Ratio http://www.transcoding.org/cgi-bin/transcode?Calculating_Frame_Size_And_Aspect_Ratio My questions were stopped in the middle because I couldn't find more time on it, and only now I managed to find some more time to follow up on the topic. Here is the situation. Suppose I have a 720x480 16:9 DVD video source, and I want to convert it to a 668x 4:3 mpeg video stream. Which example should I follow? I chose Example 5, in which the calculation consists of two steps: zooming the frame to match the new PAR, then clipping or adding borders to match the new DAR (same method with Example 6). Now, if the DVD source's aspect ratio is 4:3 instead of 16:9, there might be simpler ways, but would following Example 5 to do the calculation be wrong? I.e., would it matter for the Example 5 whether the source and destination DAR the same or not? Following Example 5, here is my calculation to convert a 720x480 4:3 DVD video source to a 668x 4:3 mpeg video stream: Note to distinguish the DAR & PAR between source and dest, I use DARs DARd and PARs and PARd to make it clearer. PAR of source 720x480 DVD video stream with 4:3 aspect ratio (DARs=4/3) is: PARs=480*4/3/720=0.888889 I want to convert to 668x480 4:3 mpeg video stream after the 2nd step padding. So, the PAR of such (destination) DVD video stream with 4:3 aspect ratio (DARd=4/3) is: width=668 height=480 PARd=$height*4/3/$width=0.958084 Now determine the zoom size for the 1st step: height = (PARd * width ) / DARs = (0.958084 * 668 ) / (4/3) = 480 This does not make sense to me, the calculated height should be smaller than 480, shouldn't it? Please see where did I go wrong. Thanks -- Tong (remove underscore(s) to reply) http://xpt.sf.net/techdocs/ http://xpt.sf.net/tools/
