why software players ignore pixel ratio of avi file

[compusic]

I just met such a problem, many software players ignore pixel ratio of avi file.
through seraching here, I find someone also mentioned this problem, but didn't give reason.


how can this happen? any official infomations?

thanks.

[mats.hogberg]

How? Because the programmers of the players are lazy, had to meet a deadline and decided drop some little noticed detail, ignorant... About as many different reasons as there are players, I'd imagine That's why I always recommend to always use 1:1 PAR in AVI, as that's the only way to be sure it will play back properly on as many players as possible.

/Mats

[jagabo]

The AVI container as defined by Microsoft does not support display or pixel aspect ratios. AVI was originally designed as a computer-only file format and assumes square pixels and progressive video. AVI was abandoned by Microsoft many years ago.

[mats.hogberg]

...but, there is such a thing as AVI PAR, and there are players that pay attention to it. Did a 4:3 CVD mpg to AVI with AutoGK, and somehow the AVI came out the same res as the source mpg - 352x576. Of course looked very stretched vertically on the computer, but the standalone player played it in nice 4:3 format on the TV.

/Mats

[jagabo]

...but, there is such a thing as AVI PAR, and there are players that pay attention to it. Did a 4:3 CVD mpg to AVI with AutoGK, and somehow the AVI came out the same res as the source mpg - 352x576. Of course looked very stretched vertically on the computer, but the standalone player played it in nice 4:3 format on the TV.

Yes, any particular codec can implement a DAR/PAR function internally. But it's not part of the AVI container. Programs have to be specifically written to the extract that information from the codec. That's why many programs do not respect the DAR/PAR flags.

[mats.hogberg]

True - I didn't think of the distinction between container and codec here.

/Mats

[compusic]

thanks for reply.

well , the dispaly problem makes me crazy.

It seems that quick time file . mov has the same problem. qt player can't recognize mov PAR. since for the same resolution files, but with different PARs, qt player displays the same size videos.

I did even more tests, and confused more.

though 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.

my brain is bleeding .......

[mats.hogberg]

[quote="compusic"]if the source video has different pixel ratio, the players will scale the video accordingly.[quote]Should. Not will.
Just find a player that does what you want most of the time. I'm confident you'll never find any kind of software that always do exactly what you want, unless you write your own! (That's how I became a developer)

/Mats

[celtic_druid]

With directshow based players, it really comes down to the filters used, not the player.

For MPEG-4, the PAR info is in the stream, so it works no matter the container but ODML avi's can actually store AR info. Think mplayer is the only player that reads them though. Don't think even VLC supports it.

[jagabo]

Media Player Classic can be set up to play videos with AR flags correctly (MPEG2 and MPEG4 for example). For files that don't have AR flags it has overrides where you can force 4:3, 5:4, 16:9, or "fit to window".

[compusic]

thanks for all your replys.

now the problem of recognizing PAR is sovled.

next is the scaling problem. as I have wrote:


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.

[jagabo]

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

Is the native resolution of your monitor 1280x1024 (5:4)? That may be complicating matters.

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!!

640 * (4/3) / (5/4) = 682. The player is adjusting the frame for a 5:4 monitor?

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.

What codec? 720x576 with 1.422 PAR is 16:9 DAR.

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.

854x480 would be 16:9 with square pixels. Once again, 854 * (4/3) / (5/4) = 910.

[compusic]

thanks for reply.

My PC is a dell model, the monitor is dell 1907fp, a 19'' LCD said to have 1280x1024 resolution. and I use digital connection for display.

yes, if the monitor is set to 800x600 resolution, those scalings seem correct.

but to my surprise, no matter what resolution the monitor is set, the number of pixels after scaling is the same.

then should I doubt what DELL has said about their monitor's resolution?

[jagabo]

With the exception of the monitors native resolution, any resolution you feed it is scaled by the monitor to its native resolution.

[compusic]

but at the monitor's native resolution, there's also scaling!!!

[Cornucopia]

...but, there is such a thing as AVI PAR, and there are players that pay attention to it. Did a 4:3 CVD mpg to AVI with AutoGK, and somehow the AVI came out the same res as the source mpg - 352x576. Of course looked very stretched vertically on the computer, but the standalone player played it in nice 4:3 format on the TV.

/Mats

mats,

In AVI v1.0 there is only DwHeight and DwWidth in vid stream header, so square pixels is assumed and the DAR is just SAR derived from these two fields.

With OpenDML (AVI v2.0), there are additional fields that can help with scaling and AR. The "video properties" header has "Video Standard" (NTSC, PAL, etc), "dwFrameAspectRatio", "FieldInfo", etc.

This is IN ADDITION to headers built into individual codec-type's video streams, like DV and DivX/Xvid/MPEG4.

A --really GOOD-- video player should look at all these fields and make adjustments based on some smart prioritizing of the values (should they have occasion to conflict).

Scott

[jagabo]

With OpenDML (AVI v2.0), there are additional fields that can help with scaling and AR. The "video properties" header has "Video Standard" (NTSC, PAL, etc), "dwFrameAspectRatio", "FieldInfo", etc.

Thanks for that info. I guess I need to study the ODML spec. I checked a bunch of AVI files that I have sitting around. The only ODML info I saw was the dmlh which only includes dwTotalFrames. Do you know any common conversion apps that include vprp (where the AR, etc are stored) or anything else?

[Cornucopia]

Here's a link to the spec: http://www.the-labs.com/Video/odmlff2-avidef.pdf.

Don't know WHICH apps do or don't support all of it. Would be interesting to find out, though!...

Scott

[jagabo]

Here's a link to the spec: http://www.the-labs.com/Video/odmlff2-avidef.pdf.

Yes, I have a copy, I've just never looked at it in detail. Thanks though.

Don't know WHICH apps do or don't support all of it. Would be interesting to find out, though!...

Nandub doesn't. Virtualdub and variants don't. I guess that means AutoGK doesn't. TMPGEnc Plus doesn't.