Even an early G4 should be able to handle MPEG-2 at DVD resolution just fine.
Other than that, in decreasing order of CPU usage:
MPEG-1
Sorenson
Cinepak
Raw/None
Which also happens to be in INCREASING order of file size, given equal resolution, frame rate, and duration. In general, the more taxing to the CPU, the better compression, therefore the smaller the file.
I can play back 320x240, 8-bit, 15 fps Cinepak on my Color Classic II just fine.
Also, MKV is another 'container' file, like AVI or MOV; it could contain any codec inside. (For example, I rip both my DVDs and Blu-rays to MKV files - the DVDs are in MPEG-2, while the Blu-rays may be in MPEG-2, VC-1, or H.264, depending on the disc.) Your MKV files probably play fine because they're DVD-quality MPEG-2 inside. If you tried to play a Blu-ray-quality H.264 MKV, your system would choke on it.
Other than that, in decreasing order of CPU usage:
MPEG-1
Sorenson
Cinepak
Raw/None
Which also happens to be in INCREASING order of file size, given equal resolution, frame rate, and duration. In general, the more taxing to the CPU, the better compression, therefore the smaller the file.
I can play back 320x240, 8-bit, 15 fps Cinepak on my Color Classic II just fine.
Also, MKV is another 'container' file, like AVI or MOV; it could contain any codec inside. (For example, I rip both my DVDs and Blu-rays to MKV files - the DVDs are in MPEG-2, while the Blu-rays may be in MPEG-2, VC-1, or H.264, depending on the disc.) Your MKV files probably play fine because they're DVD-quality MPEG-2 inside. If you tried to play a Blu-ray-quality H.264 MKV, your system would choke on it.