Changing the display aspect ratio of VCD without re-encoding

[DRP]

I have D/L'd a MPEG1 file which is set up for standard VCD (1150/224 bitrates) but its display aspect ratio has been incorrectly set at 16:9 and it should be 4:3. Other than that one thing, it could be burnt straight to disc and played as is.

Is it possible to just change the display aspect ratio of an existing MPEG1 without re-encoding it? If so, what do I need to be able to do it?

Cheers,

DRP

[mats.hogberg]

IIRC mpeg1 doesn't have DAR at all?!? Might be wrong tho...

/Mats

[bugster]

You could try a simple multiplex in TmpGenc mpeg tools. Just select the mpeg as both audio and video sources and set the type to VCD. This ought to fix it though I can't claim to have actually done this so no guarantees.

[Gideon25]

I have D/L'd a MPEG1 file which is set up for standard VCD (1150/224 bitrates) but its display aspect ratio has been incorrectly set at 16:9 and it should be 4:3. Other than that one thing, it could be burnt straight to disc and played as is.

Is it possible to just change the display aspect ratio of an existing MPEG1 without re-encoding it? If so, what do I need to be able to do it?

Cheers,

DRP

Use dvdpatcher to patch it to what you want:

https://www.videohelp.com/tools?tool=154#comments

[bugster]

I have D/L'd a MPEG1 file which is set up for standard VCD (1150/224 bitrates) but its display aspect ratio has been incorrectly set at 16:9 and it should be 4:3. Other than that one thing, it could be burnt straight to disc and played as is.

Is it possible to just change the display aspect ratio of an existing MPEG1 without re-encoding it? If so, what do I need to be able to do it?

Cheers,

DRP

Use dvdpatcher to patch it to what you want:

https://www.videohelp.com/tools?tool=154#comments

DVDPatcher
Change MPEG2 headers such as aspect ratio, resolution and more.

[FOO]

I don't think MPEG1 supports DAR either , but if it does
Restream will fix it.

[DRP]

I don't think MPEG1 supports DAR either , but if it does
Restream will fix it.

If you start up TMPGEnc and select MPEG-1 Video as the stream type you are given the following options in the drop down box for Aspect Ratio:

1:1 (VGA)
4:3 (525 line NTSC)
4:3 (625 line PAL)
16:9 (525 line NTSC)
16:9 (625 line PAL)

That would seem to indicate to me that MPEG-1 does support DAR.

[DRP]

You could try a simple multiplex in TmpGenc mpeg tools. Just select the mpeg as both audio and video sources and set the type to VCD. This ought to fix it though I can't claim to have actually done this so no guarantees.

For future reference, this doesn't work.

[Cornucopia]

Little bit of background info for you all...

1. MPEG1 supports Pixel Aspect Ratios, but not Display Aspect Ratios

e.g. ~1.095:1 (NTSC Non-square pixels) or ~.91:1 (PAL Non-square pixels), 1:1 (VGA square pixels), many others

2. MPEG2 supports Display Aspect Ratios, but not Pixel Aspect Ratios

e.g. 4:3 (Full screen), 16:9 (Wide-screen), 2.21 (Very Wide-screen), etc.

3. DVD-Patcher and ReStream will ONLY work on MPEG2 streams.

4. TMPEG allows adjustment for encoding only, not (re-)muxing.

So....Use something like MPEG Corrector, MPEG Repair, or a few other tools like that (most of them VERY obscure).

HTH,
Scott

>>>>>>>>>>edit<<<<<<<<<<<<<<<

MPEG SequenceMaker --in Debug mode

[Cornucopia]

Yep, just did another test (to assure myself of having provided a correct answer). MPEG SequenceMaker does the trick. And quickly.

*Note: Most video player apps, esp. those based on Windows Media Player, IGNORE the MPEG Pixel Aspect Ratio Flags. They just display in Square Pixel 1:1 ratio. Sometimes, they will work correctly when flipped into Full-Screen Mode, but even then there are problems.
Which apps will display correctly? For one, Quicktime. It doesn't accept ALL of the "allowable" aspect ratios, but does work for the most standard ones.

One thing you may want to check, however, is that your movie(s) may have been hard-coded as letterboxed. I know one of the test files I just tried was. Changing the PAR won't help too much there, you'll just have to crop & re-encode.

HTH,
Scott

[FOO]

2. MPEG2 supports Display Aspect Ratios, but not Pixel Aspect Ratios

You'll have to explain that one. The official term for pixel aspect ratio is
SAR (sample aspect ratio) this is the dimensions of the actual data
storage. It is obviously necessary to store the SAR in both MPEG 1 and 2
MPEG2 just has a DAR in addition.

[Cornucopia]

To clarify:

1. MPEG may officially use the term Sample Aspect Ratio to refer to the same idea as Pixel Aspect Ratio. Doesn't matter to me. The majority of working videographers, video editors and video graphics artists understand the definition of Pixel Aspect Ratio. This doesn't nullify what I was referring to.

2. While the MPEG2 spec DOES indeed include support for PAR (SAR) flags, as far as the usual MPEG2 decoder is concerned, ONLY DAR and TV system (NTSC or PAL) are referenced in determining the screen positioning/dimensions.

Example:

DVD decoder sees MPEG2 NTSC stream. It looks at DAR flags (16:9 wide-screen) and takes given resolution (720x480) and modifies it to appropriately fill the display. The PAR part can be implied in the confluence of the choice of TV system and DAR.

If you think about what the different MPEGs were created for (1--CDROM, various low-to-medium resolution multimedia devices, 2--Broadcastable, Full-screen medium-to-high resolution video and movies) it kinda makes sense.

Scott

[FOO]

I was just complaining about the inference that MPEG2 does not have a
SAR.
MPEG2 is an enhancement to MPEG1 and simply adds another
field for DAR.
Open a MPEG of any kind in Vdub and you will get the SAR

not Pixel Aspect Ratios

[DRP]

It's okay now anyway gang. I did some editing of the dodgy MPEG-1 with Womble (cutting out some frames here and there) and then resaved it out as another MPEG-1 and this fixed it. The new MPEG-1 created by Womble is right and displays correctly.

Problem sorted. Thanks for all the replies.

[Cornucopia]

That's cool FOO, that's cool DRP!

Scott