I'm a newbie and learning video encoding. I recently did 2 DVD encodes using MeGUI, one with CRF and another with 2pass-BR. The CRF encode created a rip with lower BR (1169) than the 2pass one (1900). The resulted file sizes are CRF - 954MB, 2Pass-BR - 1.37GB. The encoding settings are as below. I wonder if someone could suggest some settings tweaks for CRF to produce higher BR encode.
Thanks in advance.
Encoding settings : cabac=1 / ref=8 / deblock=1:-3:-3 / analyse=0x3:0x133 / me=umh / subme=9 / psy=1 / psy_rd=1.00:0.15 / mixed_ref=1 / me_range=28 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=0 / chroma_qp_offset=-3 / threads=3 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=0 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=10 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=240 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=2pass / mbtree=1 / bitrate=1900 / ratetol=3.0 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / cplxblur=20.0 / qblur=0.5 / vbv_maxrate=14000 / vbv_bufsize=14000 / nal_hrd=none / filler=0 / ip_ratio=1.40 / aq=1:1.00
Encoding settings : cabac=1 / ref=8 / deblock=1:-3:-3 / analyse=0x3:0x133 / me=umh / subme=9 / psy=1 / psy_rd=1.00:0.15 / mixed_ref=1 / me_range=28 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 / deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-3 / threads=3 / lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0 / bluray_compat=0 / constrained_intra=0 / bframes=10 / b_pyramid=2 / b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 / keyint=240 / keyint_min=23 / scenecut=40 / intra_refresh=0 / rc_lookahead=60 / rc=crf / mbtree=1 / crf=17.5 / qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / vbv_maxrate=17500 / vbv_bufsize=17500 / crf_max=0.0 / nal_hrd=none / filler=0 / ip_ratio=1.40 / aq=1:1.00
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CRF sets quality and you selected CRF=17.5 , so encoder responded with distributing corresponding bitrate.
Choosing lower CRF value, like 16 increases resulting quality and that will result distributing more bitrate (if you do not change settings drastically). You set it to 15 and bitrate will increase yet again etc.
There is a threshold where lowering CRF , visually you'd see very little improvement but filesize can balloon up, you waste bitrate.
Once you realize what CRF value is good for you and your DVDs, you use that all the time, because guessing bitrate for 2pass VBR you will be wrong most of the time. Different movie needs different bitrate. The margin of error towards wasting of bitrate or having not enough bitrate could be really o lot.
In CRF mode you're specifying the quality that you want. The file will turn out whatever size is necessary to deliver that quality. The size will vary depending on the nature of the particular video.
In 2-pass VBR mode you specifying the size of the file you want (indirectly via bitrate). The encoder will deliver whatever quality it can for that bitrate. The quality will vary depending on the nature of the particular video.
So they are two sides of the same coin. When the two deliver the same file size the quality is essentially the same (assuming other settings are the same).
Thanks guys. The CRF 17.5 producing the BR 1169Kb when the DVD overall BR is 6293Kb.. I just don't get it. Per my understanding the CRF 17.5 is a good number for SD DVD. I can create another encode with CRF 15 or so to check but skeptical about getting much difference in BR..
If you're using presets medium or slower you won't see much difference below CRF=17.5. As was noted with CRF the encoder uses whatever bitrate is necessary to deliver the quality you ask for. Animated material can often be compressed to very low bitrates without much loss of quality.
You haven't said how the two files look? Does the bigger file look better to you or are they both pretty much the same? As I understand it, the general consensus is that CRF values for HD sources is usually around 18 to 22 and for most SD sources is around 18 to 20. Ultimately, it's down to you. Are you happy/satisfied with the quality of the smaller file? If so then why not go with it and save time, electricity and space on your hard drive. (If you're really not sure, try viewing on other people's equipment and ask them what they think of your two encodes.)
Note that the reason HD sources can get away with slightly higher CRF values (lower quality) is because the frame won't be enlarged, or at least as much, during playback, assuming you're going to watch full screen. Enlarging a 720x480 frame to 1920x1080 enlarges any encoding artifacts, making them more visible. A 1920x1080 video isn't enlarged at all when viewing at 1920x1080.