A comparison of different codecs in QuickTime Player
Let's take a look at the exciting H.264 codec and compare it to othe popular codecs used in QuickTime movies.[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
original file
The original captured movie: (no compression, 312.29MB)

All movies below are exported from QuickTime 7 Pro with different codec. All quality settings are default settings, same dimension, and the frame rate is kept the same as the original captured movie, key frames are set to automatic.
[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
H.263
The same desktop show is exported in H.263 codec, the standard for video conferencing. iChat AV 2.1 is believed to use this codec.
watch this movie. (191.02kbits/sec, 1.03MB)

[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
H.264
watch this movie. (163.11kbits/sec, 904.92KB) (QuickTime 7 Player required to watch this movie.)

The file size saving is not great between H.263 and H.264, however, one can easily see the huge improvement over the picture quality.
To complete the comparison, we add some other popular codecs used in internet for movie delivery.
[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
Sorenson Video 3
watch this movie. (256kbits/sec, 1.38MB) (QuickTime 5+ or recent version of RealPlayer required to watch this movie.)

Sorenson Video 3 is a great codec, the picture is clear, and the file size is acceptable. However if we compare this with H.264, the file size (encoded in Sorenson Video 3) is about 56% more than the same file encoded in H.264.
It is a bit hard to compare the output difference in Sorenson Video 3 and H.264.
[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
MPEG4 (basic)
watch this movie. (68.18kbits/sec, 378.21KB) (QuickTime 6+ required to watch this movie.)

Quality is not acceptable, however, this is encoded in very low bit rate.
[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
MPEG4 (improved)
watch this movie. (277.83kbits/sec, 1.5MB) (QuickTime 6+ required to watch this movie.)

The video quality of this MPEG-4 encoded clip is a bit disappointing. However, taking that MPEG-4 is newer than Sorenson Video 3, but granted, MPEG-4 in high bit-rate can produce very good quality video.
[H263 | H264 | Sorenson 3 | MPEG 4 (basic) | MPEG4 (improved)]
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