[parsec-users] X264 is nondeterministic in terms of output size (1 thread)?

Zhunping Zhang jzz at mit.edu
Thu Jan 17 17:14:39 EST 2013


Hello,

In my experiment, I seem to have different sizes of output from different runs
of the same x264 executable. In my executions, the deterministic flag
(h->param.b_deterministic) is set to one and I only use one thread. I run the
program three times to encode eledream_640x360_128.y4m, and I got 5Mb, 5.4Mb
and 5.3Mb for output sizes.

Wonder if someone know the reason and can pinpoint me to the source?

I collected some further information to diagnose the problem. It seems that
different runs encode each frame into different sizes. The following table
shows the encoding size for the first 16 frames for three different runs.

Frame_No. 1stRun_Frame_Sizes(in B) 2ndRun_Sizes 3rdRun_Sizes
1         73623                    73623        73623
2         73518                    73518      **73519**
3         7431                     7431         ...
4         7286                     7286         ...
5         7140                     7140         ...
6         6706                     6706         ...
7         66012                    66012        ...
8         38288                    38288        ...
9         65971                    65971        ...
10        34793                    34793        ...
11        66053                    66053        ...
12        66098                    66098        ...
13        37602                    37602        ...
14        39738                    39738        ...
15        40088                    40088        ...
16        66592                  **37931**      ...

Any help will be appreciated!

- Justin




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