[Ffmpeg-devel] [PATCH] increase max numbers of B frames
Erik Slagter
erik
Wed Feb 22 19:39:31 CET 2006
On Tue, 2006-02-21 at 13:07 -0800, Loren Merritt wrote:
> Do not compare just bitrate. Remember that one of the reasons
> B-frames
> improve compression is that they allow asymmetric allocation of
> quality,
> whereby the B-frames are quantized more and the P-frames less. But if
> you
> encode with constant QP, then it quantizes B-frames more and doesn't
> change the P-frames to match, thus decreasing overall quality a
> little.
> You could encode with a different constant QP, but QP's granularity is
> too
> coarse for such a comparison.
> So run 2pass encodes with the same target bitrate, and compare PSNR
> or
> other quality metric. (That being easier than encoding with a target
> PSNR
> and comparing bitrate.) Keeping in mind that PSNR sucks, it's still
> better
> than ignoring quality entirely.
So this is what I did, I ran mencoder with this (x264enc opts) command
line with bframes = 0..5 (didn't try higher values, no interesting
results...)
-x264encopts "pass=$pass:turbo=$turbo:nofast_pskip:bframes=
$b:nr=500:bitrate=2000:vbv_maxrate=9000:vbv_bufsize=5000:scenecut=-1:threads=2"
pass = [0,1], turbo is 1 when pass is 0 and vv.
The result is that average qp goes down just a little bit when going
from 0 to 1 bframes, after that the difference really is insignificant.
Am I doing something wrong here?
Attached the relevant output.
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B frames = 0
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.38 size: 30872
x264 [info]: slice P:1992 Avg QP:26.11 size: 9936
x264 [info]: mb I I16..4: 39.2% 0.0% 60.8%
x264 [info]: mb P I16..4: 20.6% 0.0% 4.3% P16..4: 44.6% 15.5% 4.8% 0.0% 0.0% skip:10.2%
x264 [info]: kb/s:2004.0
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.25 size: 30617
x264 [info]: slice P:1992 Avg QP:25.98 size: 9926
x264 [info]: mb I I16..4: 37.7% 0.0% 62.3%
x264 [info]: mb P I16..4: 17.9% 0.0% 3.7% P16..4: 42.9% 19.1% 6.2% 0.0% 0.0% skip:10.3%
x264 [info]: kb/s:2001.8
B frames = 1
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.62 size: 31746
x264 [info]: slice P:1113 Avg QP:25.03 size: 13540
x264 [info]: slice B:879 Avg QP:27.61 size: 5327
x264 [info]: mb I I16..4: 38.9% 0.0% 61.1%
x264 [info]: mb P I16..4: 24.1% 0.0% 8.4% P16..4: 38.7% 16.5% 6.0% 0.0% 0.0% skip: 6.4%
x264 [info]: mb B I16..4: 1.8% 0.0% 1.6% B16..8: 34.4% 0.0% 0.0% direct:14.8% skip:47.4%
x264 [info]: kb/s:2000.6
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:22.25 size: 34264
x264 [info]: slice P:1113 Avg QP:24.92 size: 13420
x264 [info]: slice B:879 Avg QP:27.43 size: 5471
x264 [info]: mb I I16..4: 35.5% 0.0% 64.5%
x264 [info]: mb P I16..4: 22.3% 0.0% 7.2% P16..4: 35.6% 19.9% 8.2% 0.0% 0.0% skip: 6.8%
x264 [info]: mb B I16..4: 1.6% 0.0% 1.1% B16..8: 32.7% 1.7% 4.6% direct:10.5% skip:47.7%
x264 [info]: kb/s:2001.9
B frames = 2
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.62 size: 31692
x264 [info]: slice P:1090 Avg QP:25.05 size: 13675
x264 [info]: slice B:902 Avg QP:27.57 size: 5379
x264 [info]: mb I I16..4: 39.1% 0.0% 60.9%
x264 [info]: mb P I16..4: 24.1% 0.0% 8.6% P16..4: 38.4% 16.5% 6.0% 0.0% 0.0% skip: 6.4%
x264 [info]: mb B I16..4: 1.9% 0.0% 1.7% B16..8: 35.1% 0.0% 0.0% direct:14.5% skip:46.8%
x264 [info]: kb/s:2001.1
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:22.25 size: 34315
x264 [info]: slice P:1090 Avg QP:24.93 size: 13563
x264 [info]: slice B:902 Avg QP:27.38 size: 5513
x264 [info]: mb I I16..4: 35.6% 0.0% 64.4%
x264 [info]: mb P I16..4: 22.4% 0.0% 7.3% P16..4: 35.4% 19.9% 8.3% 0.0% 0.0% skip: 6.6%
x264 [info]: mb B I16..4: 1.7% 0.0% 1.1% B16..8: 33.3% 1.8% 4.6% direct:10.4% skip:47.1%
x264 [info]: kb/s:2003.1
B frames = 3
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.62 size: 31692
x264 [info]: slice P:1090 Avg QP:25.05 size: 13675
x264 [info]: slice B:902 Avg QP:27.57 size: 5379
x264 [info]: mb I I16..4: 39.1% 0.0% 60.9%
x264 [info]: mb P I16..4: 24.1% 0.0% 8.6% P16..4: 38.4% 16.5% 6.0% 0.0% 0.0% skip: 6.4%
x264 [info]: mb B I16..4: 1.9% 0.0% 1.7% B16..8: 35.1% 0.0% 0.0% direct:14.5% skip:46.8%
x264 [info]: kb/s:2001.1
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:22.25 size: 34317
x264 [info]: slice P:1090 Avg QP:24.92 size: 13574
x264 [info]: slice B:902 Avg QP:27.38 size: 5514
x264 [info]: mb I I16..4: 35.5% 0.0% 64.5%
x264 [info]: mb P I16..4: 22.4% 0.0% 7.3% P16..4: 35.4% 19.9% 8.3% 0.0% 0.0% skip: 6.6%
x264 [info]: mb B I16..4: 1.7% 0.0% 1.1% B16..8: 33.4% 1.8% 4.6% direct:10.4% skip:47.1%
x264 [info]: kb/s:2004.4
B frames = 4
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.62 size: 31692
x264 [info]: slice P:1090 Avg QP:25.05 size: 13675
x264 [info]: slice B:902 Avg QP:27.57 size: 5379
x264 [info]: mb I I16..4: 39.1% 0.0% 60.9%
x264 [info]: mb P I16..4: 24.1% 0.0% 8.6% P16..4: 38.4% 16.5% 6.0% 0.0% 0.0% skip: 6.4%
x264 [info]: mb B I16..4: 1.9% 0.0% 1.7% B16..8: 35.1% 0.0% 0.0% direct:14.5% skip:46.8%
x264 [info]: kb/s:2001.1
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:22.25 size: 34340
x264 [info]: slice P:1090 Avg QP:24.92 size: 13580
x264 [info]: slice B:902 Avg QP:27.37 size: 5517
x264 [info]: mb I I16..4: 35.4% 0.0% 64.6%
x264 [info]: mb P I16..4: 22.4% 0.0% 7.3% P16..4: 35.4% 19.9% 8.3% 0.0% 0.0% skip: 6.6%
x264 [info]: mb B I16..4: 1.7% 0.0% 1.1% B16..8: 33.4% 1.8% 4.6% direct:10.3% skip:47.1%
x264 [info]: kb/s:2005.3
B frames = 5
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:23.62 size: 31692
x264 [info]: slice P:1090 Avg QP:25.05 size: 13675
x264 [info]: slice B:902 Avg QP:27.57 size: 5379
x264 [info]: mb I I16..4: 39.1% 0.0% 60.9%
x264 [info]: mb P I16..4: 24.1% 0.0% 8.6% P16..4: 38.4% 16.5% 6.0% 0.0% 0.0% skip: 6.4%
x264 [info]: mb B I16..4: 1.9% 0.0% 1.7% B16..8: 35.1% 0.0% 0.0% direct:14.5% skip:46.8%
x264 [info]: kb/s:2001.1
x264 [info]: using SAR=64/45
x264 [info]: using cpu capabilities MMX MMXEXT SSE 3DNow!
x264 [info]: slice I:8 Avg QP:22.25 size: 34329
x264 [info]: slice P:1090 Avg QP:24.92 size: 13579
x264 [info]: slice B:902 Avg QP:27.36 size: 5526
x264 [info]: mb I I16..4: 35.5% 0.0% 64.5%
x264 [info]: mb P I16..4: 22.4% 0.0% 7.3% P16..4: 35.4% 19.9% 8.3% 0.0% 0.0% skip: 6.6%
x264 [info]: mb B I16..4: 1.7% 0.0% 1.1% B16..8: 33.4% 1.8% 4.6% direct:10.4% skip:47.0%
x264 [info]: kb/s:2006.0
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