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Old 3rd January 2002, 00:25   #1  |  Link
IcedT
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Setting Mpeg2 aspect ratio

Hi all,

I would like to know how change/set the aspect ratio of a mpeg2 stream (unencrypted). Is there some tool that can do that?
I'm using flaskMpeg with the LSX plugin to encode my mpg2's. The thing is that LSX doesn't set any aspect ratio flag or whatever it is, it just takes whatever it gets. In flask you can check 'Keep aspect ratio', in my case usually 16:9, but unfortunately in that cases it sends the frames with black-bars to compensate for the aspect ratio and LSX willingly encodes those too: You get letterboxed video WITH 16:9 flag so that PowerDVD adds its own letterbox-bars when playing and you get a distorted image or have to change PowerDVD's settings (then it displays correctly, but it still wastes bandwidth). When I uncheck 'Keep Aspect Ratio' in flask, only the actual data gets encoded, but without the aspect ratio data, it's a pain to play in PowerDVD (I usually encode at high quality with AC3.) I also use bbmpeg, virtualdub, avisynth, well, the usual stuff, but couln't find a solution.

Many thanks for your help!

IcedT
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Old 3rd January 2002, 00:44   #2  |  Link
xzquala
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hrmm....

seems to me that if you posted a flask question in the flask forum you might get better results.
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Old 3rd January 2002, 01:29   #3  |  Link
IcedT
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While that might be true, the flask forum is under 'DivX', but I'm concerned with MPEG2 generally... so some smart-ass could easily tell me that it's the wrong forum over there, too

Also, I'm fairly certain that flask can't do the job (since I tried every combination I found...), the same way that flask itself doesn't do multiplexing, bbmpeg does.
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Old 3rd January 2002, 01:44   #4  |  Link
xzquala
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Re:

Quote:
Originally posted by IcedT
While that might be true, the flask forum is under 'DivX', but I'm concerned with MPEG2 generally... so some smart-ass could easily tell me that it's the wrong forum over there, too
ok, here, let me try again, I have no idea but someone in the flask forum might. this is a plug in for flask you are asking about right?

just out of curiosity, why would you want to set a flag? wouldn't you prefer to just encode at the right resolution? or are you trying to author a dvd? if this is the case you may just want to go and post the question in the dvd authoring forums.
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Old 3rd January 2002, 01:46   #5  |  Link
IcedT
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Clarification

I'm not really concerned with any flask setting.
Rather I'd like to know how to change the aspect ratio of any given Mpeg2 stream. I think that it maybe is just a flag, maybe all over the file, I don't know. Maybe it isn't possible without lengthy recompile. Generally, it's more a LSX problem than flask related. And I'm not so sure if I qualify for customer support
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Old 3rd January 2002, 02:03   #6  |  Link
IcedT
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let it go, xzquala.
I appreciate your trying to help, but it really is much more complicated than that.
E.g. it doesn't have anything to do with resolution or any other newbie stuff.
MPEG2 streams have aspect ratio information inbedded in them, that tells players how to display the images. The actual video data can be quite differen, but the player 'distorts' the stream so that it conforms to the AR flag, again I don't know if it really is a flag. This process if done correctly can minimize or completely obliterate the need for letterbox bars. That's why anamorphic DVDs are better than ordinary letterboxed widescreens. They don't waste space. It's only a small, cosmetic consideration - but I'd really like to get it perfect. If you encode with bbmpg, there's a flag for that, I think, but it simply is too slow. (about three times as long)
If changing the AR information is done as quickly as multiplexing the AC3's with the video, than that would a very viable way of doing it.
And I'd like to know if there is a tool that can do that.
Enough said, cat is hungry.
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Old 3rd January 2002, 02:17   #7  |  Link
IcedT
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umm

DVD authoring *scratches head*
well, yeah, I guess what I'm doing is DVD authoring.
Never thought of it in those terms. Sounds too grand. lol.
LSX is actually a more or less professional plug-in for premiere, it also works with flask, which is very convenient.

Well, I'm tired
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Old 3rd January 2002, 06:13   #8  |  Link
Kedirekin
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I've seen a post similar to this somewhere recently. Wish I could remember where.

Anyway, what was recommended in that thread was to actually use a hex-editor to change the flag. Encode a small clip in your favorite encoder as 4:3, and then again as 16:9. Compare the two in a hex editor to find the position and value for the DAR flag, then change it in (a copy of) your full file.

I don't know enough about MPEG streams to know if this was good advice or not, but it sounded reasonable. Thought it might help.
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