What makes a good MPEG file?

[AndrewDV]

Hi,

I thought this would be a good topic. There are zillions of ways to make a MPEG file. There are also zillions of people trying different ways to do this.

How does one analyze a MPEG file to determine its full quality ratings. Obviously, one can use the "eye-ball" test to do this. What other tools are out there to give an understanding of the finished product? In conjunction to that, what would be a set of quality levels to compare? Why those levels?

I'm asking this because I showed files from various hardware and software sources to different people. Most found all sources more than acceptable.

Thank you

[wkulecz]

Two fundamental problems.

1) the very high compression of MPEG comes mostly from perceptual coding -- how much can be thrown away before people complain, so ultimately people have to debate which is "better" at a given data rate.

2) the general viewing public is amazingly uncritical as to technical quality -- otherwise VHS would have died an early death and nobody would be watching TV with "rabbit ear" antennas.

Nobody I know has had trouble deciding which encodings were "better" after a brief session where I point out the various artifacts to look for. MPEG artifacts are very different from VHS artifacts and if the viewer has never seen the high quality original there is little basis for comparison. Playing back full screen (instead of in a window) is pretty much necessary for serious evaluation. This is where its worth spending ~$65 for an OEM G450 and enabling DVDmax to a TV set.

I'm sure there are utilities to compare the reconstructed frames to the original and report some numerical "figure of merit" but I've never bothered with looking for them.

I generally stick with TMPGEnc, but sometimes I find Ligos does a better job for certain clips. CinemaCraft is out of my price range.

--wally.

[Dr Mordrid]

One tool you can use to estimate MPEG quality is BitRate Viewer. It'll show you most of the MPEG's specs plus its "Q", or compression ratio.

Just as with most other codecs the compression ratio can be an indication of quality, all other factors being equal. The shareware version shows the below stream values while the full version will also show the IBP settings.

Here is an example of the sharware BitRate Viewer output generated from an MPEG-2 DVD formatted file (Q of 4 or less is excellent quality);

Peak Q: 3.78
Avg. Q: 3.04

Num. of picture read: 107,989
Stream type: MPEG-2 MP@ML VBR
Resolution: 720*480
Aspect ratio: 4:3 Generic
Framerate: 29.97
Nom. bitrate: 9000000 Bit/Sec
VBV buffer size: 112
Constrained param. flag: No
Chroma format: 4:2:0
DCT precision: 10
Pic. structure: Frame
Field topfirst: No
DCT type: Field
Quantscale: Linear
Scan type: Alternate
Frame type: Interlaced

http://tecoltd.com/bitratev.htm

Dr. Mordrid

[wkulecz]

A nominal bitrate of 9 mb/s is only about 1/3 the 25 mb/s of DV straight from the camcorder. While I haven't investigated MPEG2 at these data rates, since I don't yet have a DVD-R, based on samples I've seen I'd be hard pressed to tell one encoder from another on video I've not see many times before. Its at VCD and SVCD data rates played back full screen where the encoder used really matters and the differences are pretty obvious.

What does bit rate viewer say about TMPGEnc vs old and "new" MSP bundled Ligos GoMotion for VCD and SVCD formats?

--wally.