QPs 52 to 69 are the virtual ones. They show up as "51" on the summary.
When I run `x264 --crf 1 --vbv-maxrate 1 --vbv-bufsize 1 --tune grain`, I get:
Code:
yuv [info]: 1280x528p 0:0 @ 25/1 fps (cfr)
x264 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
x264 [info]: profile High, level 3.1
x264 [warning]: VBV underflow (frame 0, -1800 bits)
x264 [warning]: VBV underflow (frame 1, -208 bits)
x264 [warning]: VBV underflow (frame 2, -200 bits)
x264 [warning]: VBV underflow (frame 3, -232 bits)
x264 [warning]: VBV underflow (frame 4, -208 bits)
... (warning for every frame)
x264 [info]: frame I:21 Avg QP:51.00 size: 262
x264 [info]: frame P:516 Avg QP:51.00 size: 36
x264 [info]: frame B:487 Avg QP:51.00 size: 31
x264 [info]: consecutive B-frames: 13.5% 61.7% 22.9% 2.0%
x264 [info]: mb I I16..4: 0.0% 100.0% 0.0%
x264 [info]: mb P I16..4: 0.0% 0.0% 0.0% P16..4: 0.0% 0.0% 0.0% 0.0% 0.0% skip:100.0%
x264 [info]: mb B I16..4: 0.0% 0.0% 0.0% B16..8: 0.0% 0.0% 0.0% direct: 0.0% skip:100.0%
x264 [info]: 8x8 transform intra:100.0%
x264 [info]: coded y,uvDC,uvAC intra: 0.0% 0.0% 0.0% inter: 0.0% 0.0% 0.0%
x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 0% 0% 100% 0% 0% 0% 0% 0% 0%
x264 [info]: i8c dc,h,v,p: 100% 0% 0% 0%
x264 [info]: Weighted P-Frames: Y:0.0% UV:0.0%
x264 [info]: kb/s:7.60
And the output video is not merely unwatchably low quality but rather contains no information at all: x264 quantized all of the coefficients to 0, leaving a blank grey rectangle. This
still wasn't low enough bitrate, because there is no such thing as a 1kb/s 25fps h264 video. Frame headers alone are bigger than that, before you even get to the skipped MBs which cost a fraction of a bit each.