[Ffmpeg-devel] [PATCH] increase max numbers of B frames (original) (raw)

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 -------------- next part -------------- A non-text attachment was scrubbed... Name: smime.p7s Type: application/x-pkcs7-signature Size: 2771 bytes Desc: not available URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20060222/2da56bed/attachment.bin>

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