Same file: PAR correct in VLC, MPlayer. False in QT/Perian.

[porg]

Note:

viewtopic.php?t=18847 deals with the same syndrome (wrong pixel/display aspect ratio) but I have the specialty, that I corrected the PAR with a utility, and after that playback was fine in VLC and MPlayer, but not in QuickTime/Perian. Thus I opened a new thread. I suspect a bug.


PAR modification works in VLC/MPlayer, fails in Perian

I came across a video file: AVI container, XviD codec, 544x320 native pixels, pixel aspect ratio (PAR) falsely set to 1:1, resulting in distorted playback. It should rather be 13:10.

To not have the need to correct the PAR while each playback, I wanted to permanently correct the PAR within the file, at best lossless, without the need to re-encode. I ran MPEG4 Modifier 1.4.4 obtained from http://moitah.net/ on a Windows machine, which did just that!

After the modification, playback was CORRECT in VLC 1.0.3 and MPlayer OSX Extended rev13, BUT NOT CORRECT in QuickTime Player 7.6.6 using the Perian 1.2.1 component!

Analyzing the video files with the tool VideoSpec shows the modified files with the corrected PAR as expected. See attachment.

The issue must be within Perian or QuickTime, or the hack, which MPEG4 Modifier applies, is not standard compliant, and "just works" in VLC and MPlayer, as it utilizes a supposed tolerance or even flaw of them, but considering the analysis of VideoSpec, I guess it is more likely a bug in Perian.


How I calculated the correct PAR

The video is 544px wide and 320px high, giving a DAR of 1.7.

I guess the original came from a 16/9 DAR DVD plus a "PAR stretching marker", which was lost/ignored in the transcoding process.

So the supposedly original DAR was very likely 1.78, only then the transcoder likely used some cropping and/or applied a macroblock (modulo 16) friendly width/height, and that resulted in 544/320 = PAR 1.7.

Using a playback DAR of 2.21 in VLC made it look right.

Thus I considered the original DAR and the corrected DAR, to conclude that the necessary PAR must be 2.21/1.7 = 1.30

Then I applied the 13/10 DAR on the file with MPEG4 Modifier, and after that playback was fine in VLC and MPlayer, but still distorted in Quicktime/Perian.

[Mr VacBob]

Perian almost definitely does the wrong thing here, but it's easier to ask you for your file than it is to make my own to check it. Can you post the file to Mediafire or etc.?

[porg]

The issue is currently handled in a PM session between Mr VacBob and porg.
Results of this investigation will be posted here.

[porg]

The problem seems to be that Perian doesn't parse enough of the file headers (due to historical accident).
It should be fixable, but I'm quite busy so the next Perian release won't be anytime soon.
Follow http://trac.perian.org/timeline if you're interested (and patient).

[anna23]

If i'm not mistaken the link is empty
At least I can't find any needed information there

[porg]

http://trac.perian.org/timeline by default only shows changes of the recent 7 days, and nothing has happened in this timeframe.
Simply change the filter settings (in the brown box on the right) to get results accordingly.

[porg]

And btw, in Perian 1.2.3 on Mac OS X 10.6.8 the bug still exists!
Both in Quick Time Player 7.6.6 and Quick Time Player 10.0.