Questions about settings and scenecut detection?

jassenjj · 22nd January 2012, 11:34

Hi everybody!

Be prepared - this could be a really LAME thread if you know the answer of my questions.

Occasionally I encode some vids in the last 15 years and I'm really glad that finally there are outstanding encoders like x264. I'm saying this, because I am able to tune every parameter for my encodes except the scene cut detection, which I am used to consider as important. The problem is that no matter what combination of --keyint and --scenecut values I use I always get an I-frame on each --keyint interval (tried even --scenecut values like 4000).

The goal:
1. I encode Blu ray content and I want it to be 4~6 times smaller in size than the original (should I say "... and preserve max quality"?). Actually the quality is important mainly in terms of avoiding obvious compression artifacts;
2. Source resolution and frame rate are preserved;
3. DXVA compatibility;
4. Processing time is not important.

The settings:
In this case the video has a lot of static scenes, interlaced.

Code:

--preset veryslow --tune film --crf 24 --qpmin 5 --qpmax 51 --qpstep 8 --non-deterministic 
--fps 25 --force-cfr --tff --min-keyint 5 --keyint 126 --scenecut 100 --no-fast-pskip --sar 1:1 --level 4.1 
--open-gop --b-pyramid normal --bframes 16 --ref 4 --partitions p8x8,b8x8,i4x4,i8x8 --8x8dct --subme 10 --tff
--aq-mode 2 --aq-strength 0.9 --slices 4 --rc-lookahead 60 --colorprim "bt709" --transfer "bt709" --colormatrix "bt709"

The questions:
1. Should I worry about the improper placement of the I-frames? I know that nowadays the correct detection is not so crucial for the quality, but I keep thinking that with better placement *something* could be better in the overall result? I would sleep better if I am able to set high keyint and rely on a proper scene cut detection.

2. The settings above are DXVA compatible on my configuration (I tested with ffdshow DXVA and with Daum PotPlayer). How likely it is these settings to be DXVA incompatible on different PC configurations?

And finally I'll try to explain what I consider to be an improper scene cut detection - with the above settings i get an I-frame on frames 125,250,375,500,625,750....
In the video one almost static, dark, very well compressed scene finishes at frame 490 and is replaced by another almost static very well compressed scene that seems to be very different - much more details, colors and light. Because I'm forced to use a short keyint, too often I get I-frames just a few frames before the actual scene cut and none of the information in the I-frame *seems* to be reusable.

Thank you for your answers!

nm · 22nd January 2012, 14:15

Quote:

Originally Posted by jassenjj

And finally I'll try to explain what I consider to be an improper scene cut detection - with the above settings i get an I-frame on frames 125,250,375,500,625,750....
In the video one almost static, dark, very well compressed scene finishes at frame 490 and is replaced by another almost static very well compressed scene that seems to be very different - much more details, colors and light. Because I'm forced to use a short keyint, too often I get I-frames just a few frames before the actual scene cut and none of the information in the I-frame *seems* to be reusable.

Sounds like you might be getting wrong information about frame types on playback, maybe because of B-frames and decoding vs. display order.

Could you post a sample clip?

And what's up with all these scenecut topics lately...?

jassenjj · 22nd January 2012, 16:11

Quote:

Originally Posted by nm

And what's up with all these scenecut topics lately...?

It is possible that many people are confused (or not) with the role of the I-frames in x264 and the impact on the quality and efficiency of the encoding.

Others have a real problem when it comes to adjusting subtitles manually and they would definitely benefit from a proper placement.

I can't promise example movies soon. For me it is strange that I encode 3 hours of BD movie (one disc of the BBC Life series) and there are all types of scenes - static, dynamic, bright, dark, grainy, clean... and I don't have even one I-frame that is not on a keyint interval. The final encode was done with --scenecut set to 1000 (one thousand) after I had the same behavior with lower values and larger keyints.

nm · 23rd January 2012, 02:06

Quote:

Originally Posted by jassenjj

It is possible that many people are confused (or not) with the role of the I-frames in x264 and the impact on the quality and efficiency of the encoding.

Others have a real problem when it comes to adjusting subtitles manually and they would definitely benefit from a proper placement.

I was just thinking that maybe there's an actual bug in current x264 since people are reporting all these issues with scenecut detection.

Quote:

Originally Posted by jassenjj

For me it is strange that I encode 3 hours of BD movie (one disc of the BBC Life series) and there are all types of scenes - static, dynamic, bright, dark, grainy, clean... and I don't have even one I-frame that is not on a keyint interval.

That certainly doesn't sound right.

jassenjj · 23rd January 2012, 07:53

Well... this is what I get with --keyint 276 and --scenecut 9000000. Again scenecuts are are only on keyint interval and judging from the log there are at least 3 frames that are candidates for a scenecut around the choosen one: frame 722 seems to be very "heavy" compared to the neighbours. Frame 815 is just 10 frames before the I-frame but again it wasn't a good candidate.

I would definitely be glad if somebody help me to understand this or finally expose it as a bug.

Code:

x264 [debug]: frame= 689 QP=27.63 NAL=2 Slice:P Poc:1384 I:5343 P:2683 SKIP:134  size=42870 bytes
x264 [debug]: frame= 690 QP=27.91 NAL=2 Slice:B Poc:1380 I:2075 P:3816 SKIP:2015 size=26255 bytes
x264 [debug]: frame= 691 QP=28.12 NAL=0 Slice:B Poc:1378 I:546  P:1966 SKIP:5610 size=6254 bytes
x264 [debug]: frame= 692 QP=29.42 NAL=0 Slice:B Poc:1382 I:2480 P:2501 SKIP:3098 size=16831 bytes
x264 [debug]: frame= 693 QP=27.31 NAL=2 Slice:P Poc:1388 I:4243 P:3685 SKIP:232  size=37233 bytes
x264 [debug]: frame= 694 QP=29.04 NAL=0 Slice:B Poc:1386 I:2206 P:3496 SKIP:2151 size=22423 bytes
x264 [debug]: frame= 695 QP=26.74 NAL=2 Slice:P Poc:1396 I:5424 P:2614 SKIP:122  size=44366 bytes
x264 [debug]: frame= 696 QP=28.63 NAL=2 Slice:B Poc:1392 I:2038 P:4092 SKIP:1811 size=24287 bytes
x264 [debug]: frame= 697 QP=29.04 NAL=0 Slice:B Poc:1390 I:1898 P:3595 SKIP:2482 size=20968 bytes
x264 [debug]: frame= 698 QP=29.72 NAL=0 Slice:B Poc:1394 I:1957 P:2803 SKIP:3341 size=16146 bytes
x264 [debug]: frame= 699 QP=27.94 NAL=2 Slice:P Poc:1406 I:5148 P:2789 SKIP:223  size=40717 bytes
x264 [debug]: frame= 700 QP=28.64 NAL=2 Slice:B Poc:1402 I:4614 P:2303 SKIP:1016 size=34805 bytes
x264 [debug]: frame= 701 QP=29.61 NAL=0 Slice:B Poc:1398 I:140  P:1738 SKIP:6273 size=4110 bytes
x264 [debug]: frame= 702 QP=29.28 NAL=0 Slice:B Poc:1400 I:1506 P:4247 SKIP:2170 size=21772 bytes
x264 [debug]: frame= 703 QP=30.37 NAL=0 Slice:B Poc:1404 I:121  P:1658 SKIP:6367 size=3665 bytes
x264 [debug]: frame= 704 QP=27.09 NAL=2 Slice:P Poc:1408 I:3780 P:4034 SKIP:346  size=38718 bytes
x264 [debug]: frame= 705 QP=27.08 NAL=2 Slice:P Poc:1416 I:5788 P:2191 SKIP:181  size=44497 bytes
x264 [debug]: frame= 706 QP=27.93 NAL=2 Slice:B Poc:1412 I:1741 P:4773 SKIP:1375 size=31836 bytes
x264 [debug]: frame= 707 QP=29.38 NAL=0 Slice:B Poc:1410 I:1438 P:3857 SKIP:2617 size=19934 bytes
x264 [debug]: frame= 708 QP=30.47 NAL=0 Slice:B Poc:1414 I:105  P:1935 SKIP:6114 size=4515 bytes
x264 [debug]: frame= 709 QP=27.56 NAL=2 Slice:P Poc:1426 I:4898 P:3135 SKIP:127  size=47343 bytes
x264 [debug]: frame= 710 QP=29.69 NAL=2 Slice:B Poc:1422 I:1219 P:4513 SKIP:2195 size=23694 bytes
x264 [debug]: frame= 711 QP=29.97 NAL=0 Slice:B Poc:1418 I:751  P:4201 SKIP:3007 size=16508 bytes
x264 [debug]: frame= 712 QP=29.20 NAL=0 Slice:B Poc:1420 I:179  P:1872 SKIP:6086 size=4640 bytes
x264 [debug]: frame= 713 QP=30.16 NAL=0 Slice:B Poc:1424 I:1412 P:2911 SKIP:3790 size=15216 bytes
x264 [debug]: frame= 714 QP=27.61 NAL=2 Slice:P Poc:1434 I:4534 P:3442 SKIP:184  size=42685 bytes
x264 [debug]: frame= 715 QP=27.82 NAL=2 Slice:B Poc:1430 I:1855 P:4264 SKIP:1776 size=29316 bytes
x264 [debug]: frame= 716 QP=29.48 NAL=0 Slice:B Poc:1428 I:232  P:1923 SKIP:5971 size=5425 bytes
x264 [debug]: frame= 717 QP=29.53 NAL=0 Slice:B Poc:1432 I:1772 P:3893 SKIP:2360 size=21764 bytes
x264 [debug]: frame= 718 QP=27.10 NAL=2 Slice:P Poc:1442 I:4744 P:3278 SKIP:138  size=44210 bytes
x264 [debug]: frame= 719 QP=27.94 NAL=2 Slice:B Poc:1438 I:2167 P:4067 SKIP:1705 size=29142 bytes
x264 [debug]: frame= 720 QP=30.16 NAL=0 Slice:B Poc:1436 I:1542 P:3013 SKIP:3565 size=15241 bytes
x264 [debug]: frame= 721 QP=29.21 NAL=0 Slice:B Poc:1440 I:196  P:2114 SKIP:5843 size=5436 bytes
x264 [debug]: frame= 722 QP=28.02 NAL=2 Slice:P Poc:1450 I:8091 P:69   SKIP:0    size=106610 bytes
x264 [debug]: frame= 723 QP=27.39 NAL=2 Slice:B Poc:1446 I:125  P:1769 SKIP:6261 size=4803 bytes
x264 [debug]: frame= 724 QP=30.81 NAL=0 Slice:B Poc:1444 I:74   P:1451 SKIP:6633 size=2178 bytes
x264 [debug]: frame= 725 QP=31.28 NAL=0 Slice:B Poc:1448 I:834  P:5219 SKIP:1542 size=46652 bytes
x264 [debug]: frame= 726 QP=27.83 NAL=2 Slice:P Poc:1458 I:3863 P:4109 SKIP:188  size=73567 bytes
x264 [debug]: frame= 727 QP=29.75 NAL=2 Slice:B Poc:1454 I:799  P:5916 SKIP:1084 size=46704 bytes
x264 [debug]: frame= 728 QP=31.66 NAL=0 Slice:B Poc:1452 I:193  P:5357 SKIP:2541 size=20833 bytes
x264 [debug]: frame= 729 QP=31.47 NAL=0 Slice:B Poc:1456 I:55   P:3162 SKIP:4930 size=6852 bytes
x264 [debug]: frame= 730 QP=28.59 NAL=2 Slice:P Poc:1468 I:3757 P:4315 SKIP:88   size=75266 bytes
x264 [debug]: frame= 731 QP=31.41 NAL=2 Slice:B Poc:1464 I:771  P:5610 SKIP:1334 size=40269 bytes
x264 [debug]: frame= 732 QP=31.70 NAL=0 Slice:B Poc:1460 I:175  P:5862 SKIP:1985 size=23056 bytes
x264 [debug]: frame= 733 QP=31.45 NAL=0 Slice:B Poc:1462 I:107  P:3538 SKIP:4455 size=8525 bytes
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x264 [debug]: frame= 735 QP=28.53 NAL=2 Slice:P Poc:1472 I:2321 P:5537 SKIP:302  size=60525 bytes
x264 [debug]: frame= 736 QP=30.99 NAL=0 Slice:B Poc:1470 I:139  P:3167 SKIP:4797 size=7755 bytes
x264 [debug]: frame= 737 QP=27.91 NAL=2 Slice:P Poc:1480 I:3875 P:4098 SKIP:187  size=74235 bytes
x264 [debug]: frame= 738 QP=30.60 NAL=2 Slice:B Poc:1476 I:917  P:5521 SKIP:1301 size=41422 bytes
x264 [debug]: frame= 739 QP=31.11 NAL=0 Slice:B Poc:1474 I:777  P:5322 SKIP:1690 size=30428 bytes
x264 [debug]: frame= 740 QP=31.10 NAL=0 Slice:B Poc:1478 I:639  P:5363 SKIP:1763 size=28280 bytes
x264 [debug]: frame= 741 QP=27.97 NAL=2 Slice:P Poc:1488 I:3723 P:4227 SKIP:210  size=76874 bytes
x264 [debug]: frame= 742 QP=30.75 NAL=2 Slice:B Poc:1484 I:1024 P:5459 SKIP:1266 size=42398 bytes
x264 [debug]: frame= 743 QP=31.80 NAL=0 Slice:B Poc:1482 I:320  P:5253 SKIP:2476 size=21968 bytes
x264 [debug]: frame= 744 QP=31.22 NAL=0 Slice:B Poc:1486 I:742  P:4607 SKIP:2529 size=24529 bytes
x264 [debug]: frame= 745 QP=28.78 NAL=2 Slice:P Poc:1498 I:4407 P:3719 SKIP:34   size=75099 bytes
x264 [debug]: frame= 746 QP=30.65 NAL=2 Slice:B Poc:1494 I:2613 P:4072 SKIP:1050 size=47824 bytes
x264 [debug]: frame= 747 QP=31.54 NAL=0 Slice:B Poc:1490 I:84   P:3133 SKIP:4934 size=6427 bytes
x264 [debug]: frame= 748 QP=31.33 NAL=0 Slice:B Poc:1492 I:588  P:5583 SKIP:1604 size=33927 bytes
x264 [debug]: frame= 749 QP=32.83 NAL=0 Slice:B Poc:1496 I:21   P:1465 SKIP:6668 size=2436 bytes
x264 [debug]: frame= 750 QP=28.42 NAL=2 Slice:P Poc:1500 I:2316 P:5384 SKIP:460  size=56132 bytes
x264 [debug]: frame= 751 QP=28.16 NAL=2 Slice:P Poc:1508 I:4771 P:3190 SKIP:199  size=74230 bytes
x264 [debug]: frame= 752 QP=29.48 NAL=2 Slice:B Poc:1504 I:1127 P:5551 SKIP:1041 size=51136 bytes
x264 [debug]: frame= 753 QP=31.86 NAL=0 Slice:B Poc:1502 I:305  P:5320 SKIP:2368 size=22934 bytes
x264 [debug]: frame= 754 QP=31.18 NAL=0 Slice:B Poc:1506 I:60   P:2676 SKIP:5414 size=5318 bytes
x264 [debug]: frame= 755 QP=28.89 NAL=2 Slice:P Poc:1518 I:4368 P:3673 SKIP:119  size=70602 bytes
x264 [debug]: frame= 756 QP=31.26 NAL=2 Slice:B Poc:1514 I:1043 P:5300 SKIP:1361 size=42403 bytes
x264 [debug]: frame= 757 QP=31.56 NAL=0 Slice:B Poc:1510 I:253  P:5744 SKIP:1946 size=25958 bytes
x264 [debug]: frame= 758 QP=31.18 NAL=0 Slice:B Poc:1512 I:58   P:2308 SKIP:5760 size=5396 bytes
x264 [debug]: frame= 759 QP=31.00 NAL=0 Slice:B Poc:1516 I:645  P:5369 SKIP:1953 size=26145 bytes
x264 [debug]: frame= 760 QP=28.57 NAL=2 Slice:P Poc:1522 I:2963 P:4924 SKIP:273  size=58736 bytes
x264 [debug]: frame= 761 QP=31.46 NAL=0 Slice:B Poc:1520 I:69   P:2055 SKIP:6019 size=4488 bytes
x264 [debug]: frame= 762 QP=28.10 NAL=2 Slice:P Poc:1530 I:4328 P:3656 SKIP:176  size=73195 bytes
x264 [debug]: frame= 763 QP=30.14 NAL=2 Slice:B Poc:1526 I:1291 P:5349 SKIP:1118 size=44493 bytes
x264 [debug]: frame= 764 QP=31.33 NAL=0 Slice:B Poc:1524 I:535  P:5129 SKIP:2329 size=24398 bytes
x264 [debug]: frame= 765 QP=30.75 NAL=0 Slice:B Poc:1528 I:691  P:5247 SKIP:1823 size=28662 bytes
x264 [debug]: frame= 766 QP=27.77 NAL=2 Slice:P Poc:1538 I:4411 P:3575 SKIP:174  size=72655 bytes
x264 [debug]: frame= 767 QP=30.59 NAL=2 Slice:B Poc:1534 I:1143 P:5099 SKIP:1583 size=37041 bytes
x264 [debug]: frame= 768 QP=31.45 NAL=0 Slice:B Poc:1532 I:404  P:4978 SKIP:2651 size=21656 bytes
x264 [debug]: frame= 769 QP=30.97 NAL=0 Slice:B Poc:1536 I:459  P:4298 SKIP:3235 size=18512 bytes
x264 [debug]: frame= 770 QP=29.12 NAL=2 Slice:P Poc:1548 I:4508 P:3561 SKIP:91   size=67886 bytes
x264 [debug]: frame= 771 QP=30.40 NAL=2 Slice:B Poc:1544 I:2721 P:3843 SKIP:1148 size=48399 bytes
x264 [debug]: frame= 772 QP=31.35 NAL=0 Slice:B Poc:1540 I:68   P:2564 SKIP:5513 size=5797 bytes
x264 [debug]: frame= 773 QP=30.65 NAL=0 Slice:B Poc:1542 I:759  P:5512 SKIP:1439 size=36447 bytes
x264 [debug]: frame= 774 QP=32.07 NAL=0 Slice:B Poc:1546 I:66   P:2121 SKIP:5947 size=4154 bytes
x264 [debug]: frame= 775 QP=28.16 NAL=2 Slice:P Poc:1550 I:2880 P:4912 SKIP:368  size=60181 bytes
x264 [debug]: frame= 776 QP=27.90 NAL=2 Slice:P Poc:1558 I:5488 P:2445 SKIP:227  size=68079 bytes
x264 [debug]: frame= 777 QP=29.06 NAL=2 Slice:B Poc:1554 I:1295 P:5535 SKIP:899  size=53649 bytes
x264 [debug]: frame= 778 QP=31.16 NAL=0 Slice:B Poc:1552 I:290  P:5277 SKIP:2416 size=24305 bytes
x264 [debug]: frame= 779 QP=30.93 NAL=0 Slice:B Poc:1556 I:48   P:2444 SKIP:5660 size=5254 bytes
x264 [debug]: frame= 780 QP=28.45 NAL=2 Slice:P Poc:1568 I:4753 P:3263 SKIP:144  size=66267 bytes
x264 [debug]: frame= 781 QP=30.53 NAL=2 Slice:B Poc:1564 I:1384 P:4961 SKIP:1410 size=41080 bytes
x264 [debug]: frame= 782 QP=30.83 NAL=0 Slice:B Poc:1560 I:289  P:5554 SKIP:2066 size=25923 bytes
x264 [debug]: frame= 783 QP=30.03 NAL=0 Slice:B Poc:1562 I:96   P:2359 SKIP:5660 size=6073 bytes
x264 [debug]: frame= 784 QP=31.13 NAL=0 Slice:B Poc:1566 I:527  P:4376 SKIP:3158 size=18968 bytes
x264 [debug]: frame= 785 QP=28.04 NAL=2 Slice:P Poc:1572 I:2983 P:4883 SKIP:294  size=57686 bytes
x264 [debug]: frame= 786 QP=30.65 NAL=0 Slice:B Poc:1570 I:92   P:2318 SKIP:5721 size=5569 bytes
x264 [debug]: frame= 787 QP=27.82 NAL=2 Slice:P Poc:1580 I:4237 P:3772 SKIP:151  size=67392 bytes
x264 [debug]: frame= 788 QP=29.99 NAL=2 Slice:B Poc:1576 I:1189 P:5069 SKIP:1477 size=40117 bytes
x264 [debug]: frame= 789 QP=31.09 NAL=0 Slice:B Poc:1574 I:423  P:4475 SKIP:3108 size=19142 bytes
x264 [debug]: frame= 790 QP=31.06 NAL=0 Slice:B Poc:1578 I:514  P:4719 SKIP:2535 size=22706 bytes
x264 [debug]: frame= 791 QP=27.58 NAL=2 Slice:P Poc:1588 I:4312 P:3692 SKIP:156  size=67614 bytes
x264 [debug]: frame= 792 QP=29.87 NAL=2 Slice:B Poc:1584 I:1227 P:5109 SKIP:1432 size=39426 bytes
x264 [debug]: frame= 793 QP=31.48 NAL=0 Slice:B Poc:1582 I:427  P:4654 SKIP:2925 size=19990 bytes
x264 [debug]: frame= 794 QP=31.30 NAL=0 Slice:B Poc:1586 I:444  P:3871 SKIP:3759 size=16358 bytes
x264 [debug]: frame= 795 QP=28.96 NAL=2 Slice:P Poc:1598 I:4604 P:3423 SKIP:133  size=61232 bytes
x264 [debug]: frame= 796 QP=30.00 NAL=2 Slice:B Poc:1594 I:2962 P:3597 SKIP:1253 size=45141 bytes
x264 [debug]: frame= 797 QP=31.49 NAL=0 Slice:B Poc:1590 I:96   P:1962 SKIP:6095 size=4605 bytes
x264 [debug]: frame= 798 QP=30.49 NAL=0 Slice:B Poc:1592 I:893  P:5153 SKIP:1661 size=36406 bytes
x264 [debug]: frame= 799 QP=31.39 NAL=0 Slice:B Poc:1596 I:44   P:1814 SKIP:6285 size=3393 bytes
x264 [debug]: frame= 800 QP=27.83 NAL=2 Slice:P Poc:1600 I:3780 P:4134 SKIP:246  size=55172 bytes
x264 [debug]: frame= 801 QP=27.67 NAL=2 Slice:P Poc:1608 I:5601 P:2445 SKIP:114  size=62510 bytes
x264 [debug]: frame= 802 QP=28.74 NAL=2 Slice:B Poc:1604 I:1863 P:4900 SKIP:979  size=49699 bytes
x264 [debug]: frame= 803 QP=31.24 NAL=0 Slice:B Poc:1602 I:478  P:4725 SKIP:2801 size=20790 bytes
x264 [debug]: frame= 804 QP=30.55 NAL=0 Slice:B Poc:1606 I:79   P:2240 SKIP:5826 size=4927 bytes
x264 [debug]: frame= 805 QP=28.48 NAL=2 Slice:P Poc:1618 I:4978 P:3111 SKIP:71   size=65319 bytes
x264 [debug]: scene cut at 825 Icost:2860025 Pcost:1055207 ratio:0.6310 bias:89754.5469 gop:275 (imb:2104 pmb:5684)
x264 [debug]: frame= 806 QP=30.35 NAL=2 Slice:B Poc:1614 I:1232 P:5170 SKIP:1327 size=40674 bytes
x264 [debug]: frame= 807 QP=30.96 NAL=0 Slice:B Poc:1610 I:446  P:5117 SKIP:2388 size=23869 bytes
x264 [debug]: frame= 808 QP=29.81 NAL=0 Slice:B Poc:1612 I:79   P:1998 SKIP:6058 size=4869 bytes
x264 [debug]: frame= 809 QP=30.97 NAL=0 Slice:B Poc:1616 I:390  P:4439 SKIP:3226 size=17656 bytes
x264 [debug]: frame= 810 QP=27.83 NAL=2 Slice:P Poc:1628 I:5757 P:2360 SKIP:43   size=66475 bytes
x264 [debug]: frame= 811 QP=29.73 NAL=2 Slice:B Poc:1624 I:2853 P:3966 SKIP:982  size=47462 bytes
x264 [debug]: frame= 812 QP=30.35 NAL=0 Slice:B Poc:1620 I:882  P:5303 SKIP:1549 size=34856 bytes
x264 [debug]: frame= 813 QP=30.41 NAL=0 Slice:B Poc:1622 I:667  P:5519 SKIP:1549 size=36470 bytes
x264 [debug]: frame= 814 QP=30.51 NAL=0 Slice:B Poc:1626 I:1233 P:5330 SKIP:1207 size=42379 bytes
x264 [debug]: frame= 815 QP=24.14 NAL=2 Slice:P Poc:1636 I:8142 P:18   SKIP:0    size=90658 bytes
x264 [debug]: frame= 816 QP=29.13 NAL=2 Slice:B Poc:1632 I:869  P:5259 SKIP:1886 size=34983 bytes
x264 [debug]: frame= 817 QP=31.42 NAL=0 Slice:B Poc:1630 I:163  P:4497 SKIP:3200 size=16594 bytes
x264 [debug]: frame= 818 QP=30.44 NAL=0 Slice:B Poc:1634 I:2251 P:4430 SKIP:1171 size=47540 bytes
x264 [debug]: frame= 819 QP=24.88 NAL=2 Slice:P Poc:1648 I:819  P:5717 SKIP:1624 size=37264 bytes
x264 [debug]: frame= 820 QP=29.75 NAL=2 Slice:B Poc:1642 I:207  P:3118 SKIP:4759 size=9297 bytes
x264 [debug]: frame= 821 QP=34.40 NAL=0 Slice:B Poc:1638 I:54   P:1736 SKIP:6360 size=2225 bytes
x264 [debug]: frame= 822 QP=29.14 NAL=0 Slice:B Poc:1640 I:4    P:774  SKIP:7378 size=1037 bytes
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x264 [debug]: frame= 824 QP=30.93 NAL=0 Slice:B Poc:1646 I:18   P:2212 SKIP:5910 size=3040 bytes
x264 [debug]: frame= 825 QP=21.99 NAL=2 Slice:I Poc:1650 I:8160 P:0    SKIP:0    size=119399 bytes
x264 [debug]: frame= 826 QP=25.14 NAL=2 Slice:P Poc:1664 I:1300 P:5320 SKIP:1540 size=41522 bytes
x264 [debug]: frame= 827 QP=31.99 NAL=2 Slice:B Poc:1658 I:370  P:3023 SKIP:4655 size=11305 bytes
x264 [debug]: frame= 828 QP=32.21 NAL=0 Slice:B Poc:1652 I:84   P:2693 SKIP:5344 size=5469 bytes
x264 [debug]: frame= 829 QP=31.66 NAL=0 Slice:B Poc:1654 I:176  P:3226 SKIP:4683 size=8554 bytes
x264 [debug]: frame= 830 QP=32.30 NAL=0 Slice:B Poc:1656 I:171  P:3089 SKIP:4787 size=8668 bytes
x264 [debug]: frame= 831 QP=32.17 NAL=0 Slice:B Poc:1660 I:80   P:2980 SKIP:5036 size=6521 bytes

MasterNobody · 23rd January 2012, 17:41

Quote:

Originally Posted by jassenjj

Well... this is what I get with --keyint 276 and --scenecut 9000000. ...

Don't shoot yourself in the foot and all would be OK. Hints:
1) I would say --scenecut values higher than 100 are insane;
2) flashes detection algorithm.

jpsdr · 24th January 2012, 09:55

Question about scenecut parameter : Is the value of parameter independant of image size ?
If not, for what image size the default value [40] is set for, and how it should be adjusted according image size ?

MasterNobody · 24th January 2012, 17:41

Quote:

Originally Posted by jpsdr

Question about scenecut parameter : Is the value of parameter independant of image size ?

It have nothing todo with image size.

22nd January 2012, 11:34	#1 \| Link
jassenjj Registered User Join Date: Jan 2012 Posts: 5	Questions about settings and scenecut detection? Hi everybody! Be prepared - this could be a really LAME thread if you know the answer of my questions. Occasionally I encode some vids in the last 15 years and I'm really glad that finally there are outstanding encoders like x264. I'm saying this, because I am able to tune every parameter for my encodes except the scene cut detection, which I am used to consider as important. The problem is that no matter what combination of --keyint and --scenecut values I use I always get an I-frame on each --keyint interval (tried even --scenecut values like 4000). The goal: 1. I encode Blu ray content and I want it to be 4~6 times smaller in size than the original (should I say "... and preserve max quality"?). Actually the quality is important mainly in terms of avoiding obvious compression artifacts; 2. Source resolution and frame rate are preserved; 3. DXVA compatibility; 4. Processing time is not important. The settings: In this case the video has a lot of static scenes, interlaced. Code: --preset veryslow --tune film --crf 24 --qpmin 5 --qpmax 51 --qpstep 8 --non-deterministic --fps 25 --force-cfr --tff --min-keyint 5 --keyint 126 --scenecut 100 --no-fast-pskip --sar 1:1 --level 4.1 --open-gop --b-pyramid normal --bframes 16 --ref 4 --partitions p8x8,b8x8,i4x4,i8x8 --8x8dct --subme 10 --tff --aq-mode 2 --aq-strength 0.9 --slices 4 --rc-lookahead 60 --colorprim "bt709" --transfer "bt709" --colormatrix "bt709" The questions: 1. Should I worry about the improper placement of the I-frames? I know that nowadays the correct detection is not so crucial for the quality, but I keep thinking that with better placement something could be better in the overall result? I would sleep better if I am able to set high keyint and rely on a proper scene cut detection. 2. The settings above are DXVA compatible on my configuration (I tested with ffdshow DXVA and with Daum PotPlayer). How likely it is these settings to be DXVA incompatible on different PC configurations? And finally I'll try to explain what I consider to be an improper scene cut detection - with the above settings i get an I-frame on frames 125,250,375,500,625,750.... In the video one almost static, dark, very well compressed scene finishes at frame 490 and is replaced by another almost static very well compressed scene that seems to be very different - much more details, colors and light. Because I'm forced to use a short keyint, too often I get I-frames just a few frames before the actual scene cut and none of the information in the I-frame seems to be reusable. Thank you for your answers! Last edited by jassenjj; 22nd January 2012 at 11:46.

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24th January 2012, 09:55	#7 \| Link
jpsdr Registered User Join Date: Oct 2002 Location: France Posts: 2,434	Question about scenecut parameter : Is the value of parameter independant of image size ? If not, for what image size the default value [40] is set for, and how it should be adjusted according image size ?