dvd-hq.info

compusic · Joined: 22 Sep 2006 Posts: 35

I have just done a test for doing a widescreen dvd. I let some applications to output anamorphic videos, that's 720x576 w/pixel ratio=1.422.

if I use the mpeg2 codec for output, the playback of the videos has no problem, that means when the videos are playbacked by any software players on pc and mac, the frame ratio is correct, that's 16:9.

but if I choose to output avi files uncompressed or using certain codec (the codec used here is not critical), here comes the strange thing. all the software players playback the avi files incorrectly, the displayed frame's ratio is 4:3, squeezed horizontally. both the pc and mac have the same problem. I have checked those files, yes, they are 720x576 w/ pixel ratio=1.422.

how can this happen? software players can't recognize avi files' pixel ratio? the players I have tried include windows media player 9, realplayer 10, quick time player 7, media player classic. only media player classic has the option to override the ratio, and if overrided to 16:9, that can let the video playbacked in correct ratio, but default setting "keep aspect ratio" gives the wrong result.

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and more info below.

the first video file is rendered by 3d max, using dv codec in 720x576 with pixel ratio=1.422. this file can't be playbacked by software players correctly. the frame ratio is 4:3.

then I use premiere pro 2 to creat a pal widescreen project and import that file. in premiere the file is recognized and displayed correctly, that's 16:9 ratio. then after some editting, I let premiere export movie. if mpeg2 codec is used, the playback has no problem. if output in avi format, problem occurs.

compusic · Joined: 22 Sep 2006 Posts: 35

just did another test. quicktime player and windows media player has the " save as " function, then use them to save the avi file as other 2 files, import those 2 files into premiere to check the properties.

the avi file saved by wmp is 720X576 w/ pixel ratio=1.422, nothing changed. it seems wmp only copies the origional file, since the size is the same.

the mov files saved by qt is 720X576 w/pixel ratio=1.067!!!!!
wha, quicktime player discarded the origional file's pixel ratio!!!
that's the reason, I'm afraid.

searching the net for info, I found that someone also mentioned that many software players discard avi files' pixel ratio. but didn't tell why.

anyone can explain this? any cause due to the avi standard?

thanks in advance.

RMN · Posted: Sat 10 Mar 2007, 0:25 Post subject:

I doubt 3DS MAX will even pass its internal aspect ratio value to the codec; most people using MAX (and other 3D rendering applications) don't create AVI files directly (if there is a problem during rendering and the program crashes or locks up, there's a good chance the entire AVI file will be unreadable). The "standard" procedure for 3D rendering is to save TGA (or RPF) sequences, and then load those sequences directly into editing or compositing software (which will usually let you set the aspect ratio manually).

In other words, AVI files created from 3DS MAX will not contain any aspect ratio information, which means the player will assume they use square pixels (so 720x576 doesn't even render as 4:3, it renders as 5:4).

This should be changed, of course, and it's probably trivial to do. I think there's a "wishlist" address somewhere in the 3DS MAX section of autodesk.com. You could send them a message asking them to include the render aspect ratio value in the AVI file header, but I doubt Autodesk considers it a very high-priority issue (because very few people export AVIs directly from MAX).

P.S. - If you don't have it, get GSpot. It's a small utiity that will show you a lot of information about video files and installed codecs.

RMN
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compusic · Joined: 22 Sep 2006 Posts: 35

thanks for reply.

in other forum, got the answer to the recognizing problem. that's due to as a container, both avi and mov do not support PAR info.

but there's a scaling problem.

many people have told that computers display in square pixels, if the source video has different pixel ratio, the players will scale the video accordingly. It seems definitely true, right?

then here is my test. I set my lcd monitor to 800x600, a 4:3 ratio. all videos are played at origional sizes.

first is a pal 720X576 w/PAR=1.067 mpg file, played by windows media player, check the properties I can see that the resolution is 682 x 480, not a 4:3 ratio!!

then next is a pal 720X576 w/PAR=1.422 avi file, if players discard avi files' PAR, then should use square pixel, right? check in wmp, the relosution is 640X480, wooo.... a 4:3 ratio for square pixel. but 720x576 in square pixel is not a 4:3 ratio.

next is a anamorphic mpeg2 file, 720X576 w/PAR=1.422, check in wmp, resolution is 910x480, not a 16:9 ratio. in fact, I thought this video is larger than my monitor screen can display, but to my surprise, the video didn't occupy the whole screen, there's much empty space.

and for the same avi file, qt player's window occupies more space that wmp's window. qt player only shows the video files' origional resolution, not the scaled one.

RMN · Posted: Sat 10 Mar 2007, 1:48 Post subject:

compusic · Joined: 22 Sep 2006 Posts: 35

RMN · Posted: Tue 13 Mar 2007, 5:08 Post subject:

Why would WMP scale down the image to a width of 640 or 682 pixels? If the source file is 720 pixels wide, it should be displayed with that width (at least).

At 800x600, I could understand if some parts of the interface filled the rest of the screen, and the video would have to be scaled down. But at 1280x1024, there's no reason to scale the video down automatically; it should play with its native resolution (even if the aspect ratio wasn't corrected), or scaled to (nearly) full screen.

If WMP is scaling the video down when there's plenty of free space, something isn't right.

I notice that 640 x 1.067 is 682. So it would seem that you have a 640x480 file with a 1.067 pixel aspect ratio. Not a 720x576 file (which would have been scaled to 768x576, since there is enough space on the 1280x1024 monitor).

Have you loaded the file(s) into GSpot?

RMN
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compusic · Joined: 22 Sep 2006 Posts: 35

yes, I do check those files in G-Spot.

and the numbers of pixels are 720x576 for both files.

strange!? can't figure out the reason. ;(

RMN · Posted: Wed 14 Mar 2007, 17:20 Post subject:

Have you tried other players (ex., MPC)? Looks like something wrong in WMP's configuration. For some reason it's resizing the videos down to 640x480 (although there is plenty of free space in your desktop), and then applying the aspect ratio correction.

Make sure you have "fit player to video on start" enabled, in WMP's options.

RMN
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compusic · Joined: 22 Sep 2006 Posts: 35

thanks for your patience.

I have found the cause.

the video decoder used is ffdshow MPEG-4 Video Decoder. and the "resize & aspect" option is checked. after uncheck, the numbers of pixels are correct.

In fact, I don't know how to let a player use certain decoder and/or filter, and why certain decoder becomes the default decoder.

any web page explains this?

thanks.

RMN · Posted: Wed 21 Mar 2007, 6:23 Post subject:

Different filters and splitters can cause a lot of different behaviours, so there's no simple way to explain it (things can be different depending on which order they were installed in, etc.). You can use GSpot to disable some decoders and filters, and try to resolve conflicts.

RMN
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