Where did my 16:9 go?

[Raterus]

I have a very basic question and yes I'm a noob (am I missing a college education about video processing?, I feel so stupid sometimes with all the different things you can do with video!). I'm running some AVI's I've captured from my DV camera through AviSynth, which I'm then loading the .avs file into VirtualDub to create a new AVI reflecting the changes.

Anyway, my problem is my original video is 16:9 720x480, after it runs through AVISynth the .avs file is keeping the radio, but after I "dub" this .avs to a new .avi, the final avi is "squished" together, like it's resizing the video to remove the letterbox view. I want to avoid this if possible, by keeping the aspect ratio the same and having black at the top/bottom of the video.

I'd like to know how to do this in VirtualDub. I went through about every configuration screen I could trying to figure out what was doing this, but came up blank. Can someone let me know what I'm missing here?

Thanks
--Michael

[MaximRecoil]

If you want the AVI to be 16:9 then you need to resize it, either in VDub or AviSynth. 720x405 is exactly 16:9 (1.77:1). In case you are wondering what is going on, your 720x480 video is actually 1.5:1 with square pixels. With NTSC DVD however, the pixels are not square, they have a pixel aspect ratio of 0.911. Discounting the overscan area on the sides we have 702x480 and accounting for the PAR, this gives you 1.33:1 (4:3). Now, to get to 16:9 from the NTSC standard of 4:3, the video is anamorphic which basically means it is distorted in such a way so that when it is resized by the player in real time, it looks "correct" at a 16:9 AR. What you are seeing with your "squished" AVI is anamorpic video in the "before" stage.

So, an AVI uses square pixels, so you simply resize it to the correct aspect ratio. Some codecs "prefer" the sizes to be multiples of 16 so you can try "close enough" sizes such as 720x400, 704x384, 640x352, etc; or you can figure up an exact one and see how it goes too.

[Raterus]

Thanks for your response,

Are you essentially saying my player is playing tricks on me? The original video is already squished, but the player is compensating for me by expanding the pixels so they are square? What exactly in the AVI is telling the player that it should compensate?

Is there anything I should do, or will this work itself out when it makes it to the TV? Like you mentioned, resizing works great, but should I really be doing this? I just want it to look correct when it makes it on the DVD. If my TV is going to compensate like my player is, I can live with the squish during editing.

Thanks,
--Michael

[MaximRecoil]

Are you essentially saying my player is playing tricks on me? The original video is already squished, but the player is compensating for me by expanding the pixels so they are square? What exactly in the AVI is telling the player that it should compensate?Nothing in an AVI tells the player to compensate, which is why you need to "hardwire" the size you want it to be during the encoding process (using a resize filter in AviSynth or VDub). With DVD files (VOB's and IFO's) the aspect ratio when viewed can be set with flags that the player understands. This is how they can have 4:3 video show up as 16:9 when played. Even in the case of non-anamorphic DVD video, it will be in an incorrect aspect ratio if you simply convert it to AVI, because AVI's use square pixels and NTSC DVD video does not. Anamorphic video simply compounds the problem.
Is there anything I should do, or will this work itself out when it makes it to the TV? Like you mentioned, resizing works great, but should I really be doing this? I just want it to look correct when it makes it on the DVD. If my TV is going to compensate like my player is, I can live with the squish during editing.You are converting to AVI, right? If this is the case, I assume you will be watching it on a DVD player that supports MPEG-4 and stuff, the type with a built-in file browser? If so, you need to resize the video, the same as watching it on a media player on your PC. AVI's are square pixel and have no provisions for setting flags for the player to resize them. What you see is what you get. If you are converting to AVI as an intermediary step, with plans to later author as a DVD, then your DVD authoring software can take care of your aspect ratio issues.

[Raterus]

Thanks for your insight into this, you certainly have much more experience with this than I do! I had never thought of pushing the aspect ratio issues to my DVD authoring software, I guess that would be the best solution since that's where my video will be permanently stored. I can live with some squished footage during editing.

So are you essentially saying that when I have the final mpg and it comes to writing the DVD, I can configure my DVD software to display it correctly, based on the screen size of the TV? That is, if it is a standard 4:3 TV my DVD player will add the black lines at the top/bottom?

Thanks again!
--Michael

[MaximRecoil]

So are you essentially saying that when I have the final mpg and it comes to writing the DVD, I can configure my DVD software to display it correctly, based on the screen size of the TV? That is, if it is a standard 4:3 TV my DVD player will add the black lines at the top/bottom
Yeah, in order for it to be a full D1 DVD compliant MPEG-2 stream it has to be 720x480 (4:3), so your DVD authoring software will make sure of this. Since it sounds like you are working with a 16:9 anamorphic video stream,when you encode to AVI you can leave it as is as far as the resolution is concerned; and when you author it in DVD software, "tell it" that it should be 16:9 (how to do this depends on your software); and it will put in the proper flags when it encodes it to a DVD compliant MPEG-2 stream.

[Raterus]

Thanks, you've been more than helpful!

[SeeMoreDigital]

So you're saying you have a camcorder that can capture in true 16:9, rather than 4:3?

When these camcorders first came out there were not many applications that could understand the 16:9 DV.AVI format, as they were all based around 4:3... but things have moved on now!

Even so, once the DV.AVI stream has been converted to say, an 720x480 MPEG-2 (or MPEG-4) stream, it's possible to manually alter the AR signalling flag of the stream to 16:9, if it's stuck at 4:3 ;)


Cheers

[superunknown]

Here's a small tool that'll help you calculate the new resolution
hxxp://rapidshare.de/files/3510217/VideoSizeCalc.rar.html