WMV actual vs. reported frame dimensions - how to handle?

[F. Ehrhardt]

Hello, tried Search for existing posts but could not find, so here goes.

Have some WMV files I want to shrink / join. Both File->Properties and MediaInfo report their dimensions as 720x480 (3:2), but the actual frame size is 850x480 (16:9). Some tools I have tried (Machete, SolveigMM) choke on this discrepancy - that is, the split or joined files have squeezed the images into 720x480, so people & objects are "skinny" - the original Aspect has been destroyed. Curiously, Media Player 11 isn't bothered so I guess it ignores that metadata.

Would appreciate advice on (a) tools that figure out the real frame sizes and / or (b) a tool to edit the metadata so that it accurately reflects the frame size.

Many thanks!!

[poisondeathray]

what you probably mean is the actual coded frame size is 720x480, but it is displayed as 16:9 (the media player stretches upon playback)

you can try wmvarchanger to "patch" the AR of the joined file to 16:9

[F. Ehrhardt]

Thanks for reply. I don't think the situation is as you describe. The file properties (from Explorer or MediaInfo or WMP) all say 720x480. But play the file(s) in WMP, tell it to render actual size, take a screenshot, measure the frame. It is 850x480. Thanks for tip on wmvarchanger; may try it once I wrap my head around PAR vs. frame aspect ratio.

[jagabo]

Thanks for reply. I don't think the situation is as you describe. The file properties (from Explorer or MediaInfo or WMP) all say 720x480. But play the file(s) in WMP, tell it to render actual size, take a screenshot, measure the frame. It is 850x480. Thanks for tip on wmvarchanger; may try it once I wrap my head around PAR vs. frame aspect ratio.

No, he is right. The frames within the file have a 720x480 frame size. There is a flag that tells the player to resize the image to a 16:9 aspect ratio during playback. Hence the ~850x480 result.

By the way, the situation is the same with DVDs. They are encoded with a 720x480 frame size, then flagged for either 4:3 or 16:9 display.

[poisondeathray]

Thanks for reply. I don't think the situation is as you describe. The file properties (from Explorer or MediaInfo or WMP) all say 720x480. But play the file(s) in WMP, tell it to render actual size, take a screenshot, measure the frame. It is 850x480. Thanks for tip on wmvarchanger; may try it once I wrap my head around PAR vs. frame aspect ratio.

That is what I am describing. Read up on "aspect ratios", "anamorphic" . These concepts are discussed frequently here and elsewhere

The actual coded frame size is 720x480 . This is not a square pixel format . The PAR is 40:33 (or 32:27).

16:9 NTSC DVD's work the same way

A media player will look at the aspect ratio information and "stretch" the display to 854x480 because monitors display as "square pixels". In other words, the square pixel equivalent is 854x480 (some software might display as 852 or 850px width)

Display Aspect Ratio = Frame Aspect Ratio x Pixel Aspect Ratio
16/9 = 720/480 x 32/27

The square pixel equivalent is 1:1 PAR
16/9 ~ 854/480 x 1/1

*Warning: some different terms are used for the same concept. For example PAR, pixel aspect ratio is sometimes called SAR , or sample aspect ratio. It can be really confusing, but there are different standards or nameing conventions for the same thing. But the math is always the same

[F. Ehrhardt]

Ah...so much for my novice assumptions - this is more involved than I suspected . Thanks to all for the education.

Which brings me back to why I created this thread, and hope now to make a more intelligent question. SolveigMM Video Splitter does a fine job of splitting these WMVs and saving the edited version, which plays with the right aspect in WMP. And it has IMHO a decent user interface.

But when I join several edited files into one larger WMV using SolveigMM, that resulting file plays as though the "flag that tells the player to resize the image to a 16:9 aspect ratio during playback" is not being set in the new output file.

Any suggestions either on a cheap joining app, or a way to set that "resize aspect ratio" flag in resulting file? Again, many thanks.

[poisondeathray]

Did it not work? wmvarchanger in post #2 ?

http://forum.doom9.org/showthread.php?t=116761

The other method is to use gdsmux to mux the wmv into mkv and use mkv AR flags (mkvtoolnix)


you might be able to use asfbin or movica to join the files, but they might have problems preserving AR issues as solveig (don't know)

[F. Ehrhardt]

I think I've got it... It turns out (I imagine poisondeathray saying, well, of course) according to wmvarchanger the original joined file has no aspect ratio, while the original wmv AR is reported by that utility as 1:1. I guess that means for the original, that there's some other metadata directing the player to render the desired AR.

So the [screen?] aspect ratio needs to be set to (16 / 9) / 1.5 = 1.18518519...just as poisondeathray commented:

>>Display Aspect Ratio = Frame Aspect Ratio x Pixel Aspect Ratio
>>16/9 = 720/480 x 32/27

If I set x=32, y=27 then indeed the joined video renders in WMP very close to (I'd say within 1%) of the original file's AR.

Thanks especially to poisondeathray

[poisondeathray]

There are 2 variations on PAR for NTSC

If 32:27 is slightly off, then try 40:33

40:33 is based on 704px width image (with pillarbox) , 32:27 is based on 720px width image

There is no necessarily "right" way to do things, it depends on how the file was made and processed before that. The only "correct" way is to examine some known object, like a circle , like tire or something and examine if it's distorted (e.g. oval instead of perfect circle)