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Old 19th June 2015, 18:50   #1  |  Link
gamebox
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Join Date: Nov 2011
Posts: 66
Limiting the quality of a "Fast-forward" scene

Hi everybody. I need a small advice about x264 encoding.

I have a Full-HD movie which is (sadly) done using H.263 @ 8Mbps, and I'm transcoding it to X264 @ 5Mbps, aiming to keep quality as close to original as possible by using the most advanced options X264 has to offer. Although I've done this a few times with very good results, the movie I need to process this time needs somewhat "special" treatment.

The issue is that there is a segment, several minutes in length, where movie is using some "fast-forward" like effect - that is, a regular scene is presented at speed several times over normal (many original frames are discarded). H.263 codec used originally goes all "blocky" here, probably limited by VBV, bitrate or something similar, but things on the screen are "happening too fast" for the blockiness to be obvious, and the low visual quality of the scene becomes visible only when the video is stopped. X264, on the other hand, treats this section the same way as the rest of the video, meaning it throws unnecessary high amount of bits to this scene, where the quality is already low, and it's "visual integrity" is not that important too. How can I "correct" X264s behavior so it increases quants or limits the bitrate in some way here, but not in the remaining of the video where short segments of increased complexity normally appear and need to be kept intact? I want to take away bits from that scene and redistribute them throughout the movie, where it really counts. Thanks in advance!

My options are:
cabac=1 ref=3 deblock=1:-1:-1 me=umh subme=9 psy=1 psy_rd=1.00:0.00 mixed_ref=1 me_range=32 chroma_me=1 trellis=2 8x8dct=1 cqm=0 deadzone=21,11 fast_pskip=0 chroma_qp_offset=1 threads=1 sliced_threads=0 nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 b_pyramid=2 b_adapt=2 b_bias=0 direct=3 weightb=1 open_gop=0 weightp=2 keyint=300 keyint_min=25 scenecut=40 intra_refresh=0 mbtree=0 bitrate=5000 ratetol=1.0 qcomp=0.60 qpmin=10 qpmax=51 qpstep=4 ip_ratio=1.40 pb_ratio=1.30 aq=1:1.00
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