Why x264 is much slower in 2 pass ???

[cd090580]

Hi,

I've tried the x264.exe encoder. Works great but i have a question, why is the 2 pass mode 4 times slower than the 1 pass mode ??? Theorically a 2 pass mode would be 2 times slower not 4.

I tried it with the following settings:

source: 720*576 DVD mpeg2

with 1 pass: x264.exe --bitrate 1000 --pass 1 ==> about 26 fps encoding speed
with 2 pass: x264.exe --bitrate 1000 --pass 2 ==> about 6 fps encoding speed

which such a decrease in encoding speed ???? I though i got about 12 - 13 fps

I run it on Windows 7, 1,5 GB DDR RAM on an Athlon 64 3500+

Thanks

[jagabo]

You're not comparing single pass with two pass encoding. You're comparing the speed of the first pass vs the speed of the second pass of a 2 pass encoding. The default for the first pass is to skip some of the details to make it faster. Ie, the first pass is much faster than the second pass where the real work is done. If you performed a single pass encoding it would be close to the speed of the second pass of a 2 pass encoding.