Changing AR ratio flag on MPG file

[DRP]

I've got a few downloaded MPEG files which have been encoded with the wrong DAR flag in the header so they play distorted. The idiots that made them encoded with a 16:9 flag instead of 4:3 so they play stretched horizontally. Whilst I can easily correct this by re-encoding, I was just wondering if there's any software out there that can edit the DAR flag of MPEG files without re-encoding to a new file?

Anyone know of anything that can do that?

[Baldrick]

restream or dvdpatcher

you must demultiplex the source, you can use tmpgenc for that under file->mpeg tools.

[gastorgrab]

restream or dvdpatcher

you must demultiplex the source, you can use tmpgenc for that under file->mpeg tools.

Does it also work with MPEG-1 files?

[mats.hogberg]

IIRC, mpeg1 is always 4:3...

/Mats

[DRP]

IIRC, mpeg1 is always 4:3...

/Mats

I thought that too, but apparently we're both wrong because I have here right in front of me an MPEG-1 with a 16:9 DAR as being reported by AVIcodec.

"Video : 41 MB, 1152 Kbps, 29.970 fps, 352*240 (16:9), MPG1 = MPEG 1 (VCD), Supported"

[DRP]

restream or dvdpatcher

you must demultiplex the source, you can use tmpgenc for that under file->mpeg tools.

Thanks for those suggestions, unfortunately both appear to only work on MPEG-2 files. Do you know of anything that can do the same on MPEG-1?

[gastorgrab]

You could always use a Hex Editor with the information on this page;
http://homepage.mac.com/rnc/EditMpegHeaderIFO.html

[Cornucopia]

It's right under your noses!

MPEG Sequence Maker has options for changing the AR flag (can't remember if it's PAR or DAR in MPEG1--hangover!)

Scott

[DRP]

Thanks very much for that Cornucopia, it worked perfectly. That was exactly what I was after.

I now have another question I hope you can all help with. What do I need or how can I do exactly as described above only to AVI files instead this time?

[mats.hogberg]

IIRC AVIs don't have DAR/PAR either - they always have square pixels. But I've been wrong before...

/Mats

[Cornucopia]

Windows Media Player assumes that ALL AVIs have square pixels. It actually depends on the codec's system basis when digitizing.

Example: Most codecs like Cinepak, etc expect square pixels. Systems based on broadcast video/601 have non-square pixels. Most common here are the DV codecs.

Therefore, when playing in WMP or other "dumb" players, the aspect ratio will be wrong/stretched. Sometimes this is fixed when playing in FULLSCREEN mode.

There are smarter players that understand the basis of digitization and include pixel aspect ratio compensation. Quicktime is one. It even (prematurely) lists the the "compensated" resolution as the actual resolution.

If you're worried about non-square aspect ratio on AVI's, either IGNORE the stretching, play in only SMART players (or those that allow manual PAR adjustment), or play out through to your TV (where it will be corrected).

Scott

>>>>>>>>

edit: but mats.hogberg was correct in that there is NO flag available with AVIs that denote PAR. It is just implicit (and therefore subject to misinterpretation).

[DRP]

Sorry, I should have been more specific. I didn't realise we were talking about pixel aspect ratios. To be honest I didn't even know there was such a thing. I thought I was adjusting the display aspect ratio on the MPEG before not anything to do with pixel shape.

Anyways, I have an AVI file here which has been encoded with a DAR of 16:9 *but* somewhere along the line it must at one time have included a 4:3 amount of black bar letterboxing because it displays at an aspect ratio of 3.16:1 (1.778^2). The video itself is of a 2.35:1 AR so it displays too wide by a factor of 4:3. I'm using MPC to play it on the computer.

How can I adjust the headers of the AVI to make it display at the correct 2.35:1 AR instead of 3.16:1?