Faster Than Real-Time: MPEG-4 Encoding With DivX 4.11

DVD2AVI 1.76 - Connections Between PAL And NTSC

While converting, we noticed something very interesting - we compared a PAL DVD (Europe) with an NTSC DVD (North America). Both DVDs contain the same movie. While the CPU barely reached the 25 fps barrier on the PAL DVD, it managed to hit 30 fps with the NTSC version. Despite the fact that it was the same movie, the conversion surpassed the real-time barrier in both instances. The frame rate for PAL is 25 fps, while 30 fps is the rate for NTSC. These rates aren't anything unusual, but are based on physical principles. The following formula should explain this somewhat:

*PAL pixel rate: 720 x 576 Pixel x 25 fps = 10.4 MPix/s*NTSC pixel rate: 720 x 480 Pixel x 30 fps = 10.4 MPix/s

In the same color space, the pixel rate is directly proportional to the bit rate. In other words, it makes no difference whether your video is in PAL or NTSC format. If a CPU manages to break the real-time limit for a video format such as PAL, it should be able to do the same for NTSC. Please note the video format we refer to for each benchmark.

Tip for all our persnickety readers: According to the NTSC specifications, the frame rate is actually 29.97 fps, but this formula is still a meaningful approximation.

When used with the 4.02 version of DivX, the Pentium 4/2000 still can't quite catch the Athlon 1900+/2000+. It isn't until DivX 4.11 gives it a boost that it manages to overtake the competition. When not converting audio signals, all the CPUs exceed the real-time limit (30 fps for NTSC) in YUV color space. Even if the Pentium 4/2000 is head and shoulders above its opponents, the Athlon XP owners can also see some improvement.

Uwe Scheffel