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Old 27th December 2012, 12:12   #1  |  Link
h3nry
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Join Date: Dec 2012
Posts: 16
how to know the crf of a video

I'm just a beginner in video encoding and I have many doubts

I've a lot of videos,hd and sd,downloaded from youtube,recorded...and i'm running out of space.so I want to compress the videos as much as possible without quality loss.

first I tried to re-encode a 720p video of 3012kbps using Handbrake v0.9.8 with crf=19.0,without changing the resolution.I used extreme x264 settings and I spent hours for encoding expecting huge decrement in size but the re-encoded video turned out to be nearly double the size.here's the settings I used:-

Encoding settings: cabac=1 / ref=6 / deblock=1:-3:-3 / analyse=0x3:0x133 / me=umh / subme=10 / psy=1 / psy_rd=1.00:0.20 / mixed_ref=1 / me_range=64 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-3 / threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=5 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=1 / weightp=2 / keyint=infinite / keyint_min=25 / scenecut=40 / intra_refresh=0 / rc_lookahead=250 / rc=crf / mbtree=1 / crf=19.0 / qcomp=0.60 / qpmin=3 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00 plus I set the interlacing & decombing filters to default.

so I guessed the problem will be with the crf value I use and I tried 21 and 23.but the size is still bigger than the source! so I chose handbrake's high profile settings and let it choose the default settings except I altered ref=1,which is same as source.after many trials i found that a crf value of 25.4 produces a video with same bitrate as the source thus same size(25.4 is way too far than the recommended value).does that mean the encoded video and the source will be of same quality?but after analysing some screen shots it seems there is some loss in detail in high motion scenes even though majority of the frame seems intact.its the property of crf,right?it takes details from high motion scenes where we will hardly notice and thus saving bits creating a vbr mode.or is it quality loss?note that the source is also in variable bitrate mode.

or is the increase in size due to some other issues?please help.is there any recommendations on the settings I use?

Last edited by h3nry; 27th December 2012 at 12:15.
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