Increase the resolution of default timebase

The old value 1000 was too low, which caused the effective duration and
frame rate calculation to have an 1% error for typical 30 frame/second
inputs. Symptom of the issue has been that most 2 pass encodings were
undershooting target bit rate by 1% or so for 30 fps input.

Change-Id: Ice204e86f844ceb9ce973456f2b995cc095283cf