AVI v.s. MPEG

[moviebuff2]

Would someone please help my solve this mystery?

Recently, I converted an AVI file to MPG. The result was an MPEG file that is 3X the size of the AVI. I used AVI2VCD version 1.4.3.

So, I reasoned that AVI files must be more compressed than MPEG files.

I just converted an MPEG file to AVI (this is a completely different file from the one above). The result is an AVI file that is 20X the size of the MPEG file. I used TMPGEnc.

My question is: which format is more compressed?

Thanks

[moviebuff2]

Sorry this somehow got posted twice. Please delete one of them. Thanks.

[MpegEncoder]

Both AVI and MPEG are compressed video with compressed or uncompressed audio (usually compressed). The video compression varies based on the technique used. Like for MPEG, the bitrate will affect the the size of the output. As will VBR/CBR. Similar things apply to AVI (which is just a container).

Bottom line is you need to know that the compression types are for both file types.

P.S. An AVI video could also be uncompressed but that would be huge and most ppl would not use that.

[Gurm]

Ok, let's talk some generalities. All of this is subject to the YMMV rule, as well as others.

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MPG files are compressed with standard MPEG compression. The size of the file is directly proportional to the size of the video. The compression of the video is done with either MPEG1 or MPEG2 compression, and the audio is either uncompressed or compressed in one of a couple standard ways.

Now your standard VCD-size MPEG file (352x240, MPEG1) is around 10megs a minute.

AVI files can be uncompressed, lightly compressed, or heavily compressed. Modern AVI codecs (encode/decode filters) allow for pretty heavy compression with great video quality - at the expense of requiring a hefty CPU load to decode them. MPEG1 requires nearly no CPU overhead on a modern machine. MPEG2 at DVD resolutions can be decoded just fine (with 6-channel audio, no less) by a P3-500. But a fullscreen XVID with tight compression - that requires a fair bit of CPU usage, even on a modern box.

So it's all a trade-off.

When you used TMPGEnc to output to an AVI file, you either used "no compression" (the default) or picked some other light-compression method, which resulted in a very large file - but which also can be decoded very easily with little CPU power.

It's all a trade-off.

Sorry, I know this is rambling. Feel free to ask followup questions, so that I can give a more focused/coherent answer!

[MpegEncoder]

MPG files are compressed with standard MPEG compression. The size of the file is directly proportional to the size of the video. The compression of the video is done with either MPEG1 or MPEG2 compression, and the audio is either uncompressed or compressed in one of a couple standard ways.

Now your standard VCD-size MPEG file (352x240, MPEG1) is around 10megs a minute.

Somewhat true, but not complete. The output file size is always some direct ratio of the size of the input file (which really doen't say much).

VCD is mpeg-1 CBR (constant bit rate) at a fixed rate of 1.15Mbps.

DVD's use mpeg-2 and allow a variable bitrate (which is useful to optimize space). Since the bitrate is not fixed, the size of the output is determined by the bitrate used.

Lower bitrate = smaller file with potentially less quality (depends how low you go).

Higher bitrate = larger file (with generally better quality).

[Gurm]

Yes I knew I was forgetting something.