Resizing 704x480i keeping correct aspect ratio

[wbo]

I have been capturing HDTV transport streams and encoding them using xvid for archiving. Up until now all the streams I have been working with have been 1920x1080i telecined film. So, I have been using AVISynth along with Decomb to restore the progressive frames and resizing to 1280x720 before encoding.

Now I have several 704x480i transport streams that I also want to encode with xvid. However, I am not sure what the proper pixel aspect ratio is for 704x480i DTV streams.

I know that 1920x1080 streams have a 1:1 pixel aspect ratio (1920/1080 = 16/9). But 704/480 does not equal 4/3 or even the NTSC equivalent of 3/2. Are 704x480i streams supposed to have a 1:1 pixel aspect ratio?

I would like to encode the strings with a 1:1 pixel aspect ratio for playback on a PC monitor, so I need to know what the pixel aspect ratio of the streams are so I can calculate what resolution I should resize them to. If the streams were NTSC 720x480 I would of course resize them to 640x480, but I am not sure what I should do with the 704x480i streams.

[bugster]

I would like to encode the strings with a 1:1 pixel aspect ratio for playback on a PC monitor, so I need to know what the pixel aspect ratio of the streams are so I can calculate what resolution I should resize them to. If the streams were NTSC 720x480 I would of course resize them to 640x480, but I am not sure what I should do with the 704x480i streams.

Not an expert on divx/xvid encodeing or HDTV but here are a few ideas.

AFAIK, HDTV transport streams are mpeg encoded which means they carry a Displa Apsect Ratio flag that will be either 16:9 for widescreen or 4:3 for normal display. I don't know if HDTV allows any other DAR's, it may. But this information is important in deciding the resolution when encoding for PC display. If it is 4:3, then 640*480 would be a good choice, but if it is 16:9 then 852*480 would be better whilst preserving the original Display ASpect ratio.

[edDV]

704x480 is the normal SDTV frame size for DTV (16:9 & 4:3) and also part of the DVD specification. A DVD player or computer player like PowerDVD will resize the image correctly. In that case resizing to square pixels is not necessary and burns the bridges for going back to DVD without another resize.


http://www.mir.com/DMG/aspect.html
http://www.lurkertech.com/lg/pixelaspect.html
https://www.videohelp.com/forum/userguides/174200.php
http://www.doom9.org/index.html?/capture/sizes_newbies.html

[Cornucopia]

As ALL HDTV formats are 16:9, you could always force your encoder to set that DAR.

As edDV said, 704x480 (as well as 720x480) in DVD, supports both 4:3 and 16:9. If you're going straight from MPEG2 (HDTV Transport Stream)-->MPEG2 (SDTV/DVD Program Stream) you would probably retain the correct DAR flag. If you are going to an intermediate AVI or something, that will be lost and you will have to manually specify it.
But it sure sounds like it should be set to 16:9.

Scott