x264 & meGUI

[edekba]

Hmm I was wondering why does meGUI using x264 give a bitrate so much lower than the target. Here is the command log file.

"--pass 1 --bitrate 1798 --stats "G:\temp\XMENSE_DISC1\VIDEO_TS\xmen.stats" --bframes 2 --direct auto --nf --no-cabac --subme 1 --analyse none --qpmin 18 --vbv-maxrate 25000 --qcomp 0.3 --me dia --threads 2 --thread-input --progress --no-psnr --no-ssim --output NUL "

and after the 1st pass it says this.
"encoded 150067 frames, 30.29 fps, 1157.22 kb/s"

2nd pass command line is
"--pass 2 --bitrate 1798 --stats "G:\temp\XMENSE_DISC1\VIDEO_TS\xmen.stats" --no-fast-pskip --bframes 2 --b-rdo --bime --direct auto --nf --no-cabac --subme 7 --analyse all --8x8dct --qpmin 18 --vbv-maxrate 25000 --qcomp 0.3 --me umh --threads 2 --thread-input --progress --no-psnr --no-ssim --output "G:\temp\XMENSE_DISC1\VIDEO_TS\xmen.mp4" "

The Result is
"avis [info]: 720x384 @ 23.98 fps (150067 frames)
x264 [info]: using cpu capabilities MMX MMXEXT SSE SSE2
x264 [warning]: VBV maxrate specified, but no bufsize.
x264 [warning]: Error: 2pass curve failed to converge
x264 [warning]: target: 1798.00 kbit/s, expected: 1332.02 kbit/s, avg QP: 18.0040
x264 [warning]: try reducing target bitrate or reducing qp_min (currently 18)
mp4 [info]: initial delay 1001 (scale 24000)
x264 [info]: slice I:1839 Avg QP:18.00 size: 17519
x264 [info]: slice P:66933 Avg QP:18.00 size: 8184
x264 [info]: slice B:81295 Avg QP:20.00 size: 2675
x264 [info]: mb I I16..4: 45.4% 28.3% 26.2%
x264 [info]: mb P I16..4: 6.5% 6.7% 4.4% P16..4: 25.1% 12.7% 1.8% 0.4% 0.2% skip:42.2%
x264 [info]: mb B I16..4: 0.4% 0.7% 0.4% B16..8: 24.2% 1.5% 2.2% direct: 2.5% skip:68.0%
x264 [info]: 8x8 transform intra:37.5% inter:43.9%
x264 [info]: direct mvs spatial:63.2% temporal:36.8%
x264 [info]: kb/s:1019.3

encoded 150067 frames, 8.69 fps, 1019.37 kb/s

desired video bitrate of this job: 1798 kbit/s - obtained video bitrate (approximate): 1021 kbit/s"


I set a target of almost 1800 and it came out as only about 1000? Is this normal?

[Sharktooth]

Remove qpmin 18

[edekba]

thanks, i'll try that.

[foxyshadis]

You probably won't see any difference between 1000 and 1800 at that rate, so forcing twice the size is kind of silly. Maybe you should use a larger video frame, don't resize down quite so much? That can make an instant quality gain.

[DarkZell666]

@edekba : why is it a problem when the quality is near-perfect ? (your log states average QP = 18.xxx which is very good) ;)
The explanation is simple : your source is probably very clean, so x264 simply didn't need all the bitrate you asked for to achieve a very decent quality.

By default qpmin is 10, which is too low imho, since I can't see too much of a difference between QP10 and QP18 without zooming in, and eats up bitrate almost for nothing. (qpmin 15 would be the lowest I'd go).

The only thing you could do about your resolution is to encode anamorphic (720x576 or 720x480) instead of re-scaling vertically. Upsizing isn't something I would do (though some people here do that indeed, and are happy with that). Oh well, when I get an HDTV I'll probably change my mind, but until then ...

In fact, I'm extremely surprised about your logfile, since you disabled cabac and inloop filter and still got an insanely low bitrate considering your source ... w00t x_o