Basic avi to mpeg questions

[hankys]

Hello,
I have a few questions regarding .avi files;
What is the difference between a traditional avi file and a DivX avi file? Which produces a better mpeg 1 or mpeg 2 file? How does one tell which is which?

Finally, when you are downloading an mpeg file, how does one tell whether or not it is an mpeg1 or mpeg2 file?
Thanks!

[Truman]

DivX is an AVI compression codec.
At same bitrate/ resolution there is no difference between MPEG-1/ MPEG-2.
VCD standard requires MPEG-1
SVCD standard requires MPEG-2
Open a MPEG in TMPG's demultiplex dialog to see, which MPEG format you have.

<font size=-1>[ This Message was edited by: Truman on 2001-10-01 06:43:20 ]</font>

[hankys]

Thanks.....can all avi files be converted to MPEG-2 format? For example, is it possible to convert an MPEG-1 to an AVI file. Can that AVI file then be converted to MPEG-2? And if so, will that MPEG-2 file have similar video quality as an MPEG-1 file made from the same avi file?
thanks

[Truman]

Avi->MPEG-2 / MPEG-1->AVI / MPEG-2->AVI / MPEG-1->MPEG-2 / MPEG-2->MPEG-1.....
Everything is possible, with every conversion you'll loose some quality. More or less, depends on the encoder and its settings.
As I said, at same resolution/ bitrate a MPEG-1 has the same video quality as a MPEG-2 in theory. But one encoder has a better MPEG-1 output, the next has a better MPEG-2 output. And some encoders suck at all...

[xaanin]

Truman, I remember reading that MPEG-1 was more optimized for bitrates <2200, and MPEG-2 for bitrates >2200, is that true?

[hankys]

Great, thanks.....

[Truman]

xaanin, yes there are some slight compression improvements over MPEG-1. MPEG-1 was optimized for a bitrate of
about 1.5 Mbit/sec. That's why 1150kbit/sec+224kbps became the standard of VCD. MPEG-1 was also designed to be used with small image sizes like 352x240/288. MPEG-2 is
optimized for higher bitrates. Since SVCD and most dvd players (when playing SVCD) are limited to about
2750 kbps over all bitrate, I can not use the real advantages of MPEG-2, when really high bitrates like 6000 kbps come into the game. From my own experience I can say, in the range from 1300-2500 kbps there is no difference
between MPEG-1 and MPEG-2.

[thxkid]

I have compared the same video image at 2520 of a MPEG1 at 352x240 and a 2520 MPEG2 at 480x480 and the MPEG2 is sooo much sharper than the MPEG1, to get MPEG1 to look sharp I have had to use Edge Enhancement in TMPGE when encoding to MPEG1 to get a some what sharp picture. This is using a high quality a source also like Hi8mm, SVHS, DVD or Laser Disc. I imagine if you are using VHS you won't see much differnece since VHS is of Sub par quality anyway(I never use just VHS)

[Truman]

<TABLE BORDER=0 ALIGN=CENTER WIDTH=85%><TR><TD><font size=-1>Quote:</font><HR size=1 color=black></TD></TR><TR><TD><FONT SIZE=-1><BLOCKQUOTE>
On 2001-10-01 10:37:35, thxkid wrote:
I have compared the same video image at 2520 of a MPEG1 at 352x240 and a 2520 MPEG2 at 480x480 and the MPEG2 is sooo much sharper than the MPEG1.....
</BLOCKQUOTE></FONT></TD></TR><TR><TD><HR size=1 color=black></TD></TR></TABLE>
Sure your MPEG-2 is sharper. It is sharper due to the higher resolution. Please compare next time MPEG-1 480x480 to MPEG-2 480x480 @ same bitrate (same source).