sneaker_ger
6th March 2009, 15:46
Ok, found it:
The reason is because CRF weights frame quantizers by overall frame complexity.
Having large black areas in a frame makes it simpler, so CRF lowers the quantizer.
Thus, the only valid way to measure the effect of the black areas on compression is constant-quantizer encoding, or qcomp=1 encoding with CRF.
/edit:
Found another post, saying it doesn't add black borders:
x264 doesn't mirror, it pads with repeated lines. Mirroring makes more sense for JPEG and intra-only formats in general.
I'll think it's still possible that is has something to do with the way CRF works, but I don't have enough knowledge to be of any help here. Perhaps some x264 pro can elaborate on this.
The reason is because CRF weights frame quantizers by overall frame complexity.
Having large black areas in a frame makes it simpler, so CRF lowers the quantizer.
Thus, the only valid way to measure the effect of the black areas on compression is constant-quantizer encoding, or qcomp=1 encoding with CRF.
/edit:
Found another post, saying it doesn't add black borders:
x264 doesn't mirror, it pads with repeated lines. Mirroring makes more sense for JPEG and intra-only formats in general.
I'll think it's still possible that is has something to do with the way CRF works, but I don't have enough knowledge to be of any help here. Perhaps some x264 pro can elaborate on this.