MPEG-1 and MPEG2 file differences
 

I'd pretty much been using Mpeg-2 as my dvd player won't play anything but standard VCDs, but will play almost any kind of SVCD, until someone pointed me in the direction of the header trick.

I get some quite strange results after doing this. Basically, I encoded a file using a KVCD template (but fiddled with the resolution), and got a mpeg-1 file that was 887 meg. After using TMPGenc to do the header trick, the file size is 546 meg. I'm not complaining, I just don't understand.

What version of tmpg are you using?
(2.59 has vcd muxing bug wich actually muxes it as mpeg1)

When you mux an m1v or m2v with audio to the desired mpeg format
like mpeg1, vcd, mpeg2, or mpeg2,
the file gets padded with bits for the appropriate format.

The result usually causes the file to grow in size just a little bit
due to the padding, but smaller, uh ohhh...

-phibertron

The thing I've found, and this is probably old news to everyone here, is that if I encode a movie as MPEG-1, then as MPEG-2 using identical settings, the MPEG-2 file is considerably smaller. The MPEG-1 file may well look a bit better, but I can up the settings for the MPEG-2 file and get a much better bitrate with the same file size.

For example, a movie I did using the PAL kvcd template, had a bitrate of around 2000 and a CQ of around 50. It fitted on one CD (100 minutes or so), and looked reasonable. I then did the same movie as MPEG-2, but was able to up the bitrate to nearly 3000 and the CQ to 80, and the difference was enormous. The quality was so much better. It still fitted on one CD. Could it be my player just doesn't care for MPEG-1?

no that's not possible :wink:
check your results, because an MPEG-1 file should always look better at low bitrates (which you certainly have, fitting a movie on 1 CD), compared to an MPEG-2 file. The filesize will always be slightly SMALLER for the MPEG-1 file. Are you sure you are using the same resolution / framerate / CQ for both?
you also need to watch out, as you might encode as Interlaced when using MPEG-2, which will also lead to a smaller filesize, but which is not recommended for VCD/SVCD.
I don't think that you can use an average bitrate of 3000kb/sec for a movie on 1 CD, unless it's no more than 30 min. long... you must be mistaken there. see if you made any errors in your observations :!: :wink:

Well, I'll double double check everything, but I'm fairly certain that the results I'm getting are correct. What I can say for definite, is that if I de-multiplex an 800 meg KVCD, and multiplex it as an SKVCD, it'll be around about 600 meg. Unless I'm completely losing it.

The file size difference is due to padding :!:

In the other case it is needed and in the other it is not.

This is the first I had heard of this! I encode 99% of my KVCD's as Interlaced (544x480). Does this mean I am doing something wrong? Should I be adding FieldDeinteralce () to all my scripts ?!?

Thanks,
Icarus

I also always use interlace.

I should point out that the SKVCDs of 3000 max bitrate and CQ of up to 80 are using the KVCD resolution, ie 352x288.

I just load the kvcd template, and change the format to mpeg-2 and the system to SVCD. ( i also up the DC Component to 10, as this makes a hell of a difference in quality IMO)

As for padding, are you saying MPEG-2 doesn't use padding? If I forget to change the system to SVCD and leave it at MPEG-2, VCDEasy says it'll pad it for me on the fly.

Padding depends on the encoded file. I don't remember what exactly causes padding to happen, but I think that if the VBV buffer is low (~22KB) and your max bitrate is high (>2000), padding may occur. I'm sure someone will be able to explain this better. VCD and SVCD use different mux settings.

Now we're talkin! I thought you meant an Average Bitrate of 3000kb/sec...
ok, here are my 2 cents : at this low resolution (352x288) it might actually be possible that MPEG-2 will look slightly better, since the I-Frames of an MPEG-2 file are less blocky. However, you should use blockbuster for such a low resolution in MPEG-1 which will give you excellent quality.
Have you actually compared the 2 files on a TV, using File Prediction on both of them, so that both fill out the full CD? Try that again!
I really don't want do offend anyone, or sound like smart-ass to you.

As for the Interlacing. don't get me wrong guys. in my eyes it's a simple rule. Encode Interlaced material with interlacing, and progressive material with no interlacing. Since I live in a PAL region, almost no interlaced material here. you're not doing anything wrong guys, I'm sure! 8)

Sorry, I didn't mean average bitrate.

I have compared the two, and on my player, the MPEG-2 looked better, HOWEVER, in hindsight, this could be because I'd always been using interlaced mode. The interlaced MPEG-1 was terrible quality, all shaky and glitchy, so I'll give it a go non-interlaced, and compare the results.

I'm sure in general, that comparing MPEG-1/2 using identical bitrate and CQ levels, will show the MPEG-1 to be better, however, my original query was regarding the file sizes. The MPEG-2 file is considerably smaller, so I can afford to up the bitrate etc to levels that would push the MPEG-1 file over the 1 CD mark. Although, the MPEG-2 does look a little blurry, not too bad, but I assumed this was due to the resolution.

Cheers.

MPEG-1 doesn't support interlaced content! That's why it didn't look good at all.

Hmmm... I couldn't find reference to this anywhere else in these forums, why do you say MPEG-1 doesn't support interlaced?

I usually encode my KVCD's as MPEG-1 interlaced @ 544x480, and haven't had a problem.

Thanks,
Icarus

It's doesn't :!:
MPEG-1 was defined as progressive(non-interlaced) only. It's in the MPEG-1 specifications :!:

-kwag

Kwag:

Maybe I missed it somewhere in the guides, but does this mean that I should ALWAYS encode KVCD's as non-interlaced ??

Just when I thought I had the hang of this, I am now very confused again!

Thanks,
Icarus

You don't have any choice if you're encoding MPEG-1 :)
TMPEG will ALWAYS encode MPEG-1 as progressive. You can't change any options :!:
Take a look under Settings/Video tab, and you'll see that the "Encode mode:" is grayed out, and you can't change it. Only if you select MPEG-2 you will be able to make changes :wink:

-kwag

Is it greyed out because these options are no longer relevant? Or because you just shouldn't change them? If I change it to MPEG-2, change it to interlace, then back to MPEG-1 again, it'll be greyed out but still say interlace. Likewise with the DC Component setting (I always up it to 10).

It's greyed because not relevant in MPEG1.

Maybe I have been asking the wrong question. :?

When encoding an interlaced source to MPEG-1, do I need to do anything specific to "De-interlace" ? (ie: use decomb.dll in the .avs script). Or does it not matter since the final product will be progressive ?

Thanks,
Icarus

i do not use deinterlace when encoding an interlaced source to mpeg1
no problems till today