The private options chromaoffset, sc_threshold, and noise_reduction were set to 0 rather than -1, and were always initializing values in libx264 rather than letting the library use its default.
b340bd8 libx264: Make sure to preserve default option values
libavcodec/libx264.c | 11 +++++------
1 file changed, 5 insertions(+), 6 deletions(-)