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Old 2007-03-04, 20:28   Link #761
Junior Member
Join Date: Mar 2006
What do you people think about using a 2-Pass encode that have Quantizer Minimum 18 and Quantizer Maximum 24?

QP 18 = enough quality for our eyes
QP 24 = double compression compared to the QP 18

I downloaded the latest Manabi Straight raw from the l33t-raws torrents and encoded this file changing the resolution to 640x480 with LanczosResize and using QPMin 18, QPMax 24 and 2-Pass encode with target bitrate for a 175 MB filesize and I got this.

avis [info]: 640x480 @ 23.98 fps (34884 frames)
x264 [info]: slice I:319 Avg QP:18.01 size: 24106
x264 [info]: slice P:18634 Avg QP:18.03 size: 4777
x264 [info]: slice B:15931 Avg QP:19.70 size: 1544
x264 [info]: final ratefactor: 18.00
x264 [info]: kb/s:667.0

avis [info]: 640x480 @ 23.98 fps (34884 frames)
x264 [warning]: Error: 2pass curve failed to converge
x264 [warning]: target: 913.00 kbit/s, expected: 701.69 kbit/s, avg QP: 18.0000
x264 [warning]: try reducing target bitrate or reducing qp_min (currently 18)
x264 [info]: slice I:319 Avg QP:18.00 size: 22476
x264 [info]: slice P:18634 Avg QP:18.00 size: 4377
x264 [info]: slice B:15931 Avg QP:19.67 size: 1343
x264 [info]: kb/s:605.6

It gave me the message saying that the bitrate inserted for a 175 MB is too high for the QPMin 18 compression used on this episode but I dont think this message is a problem because that is what I wanted the encode is only using the necessary bitrate and it is not wasting bitrate on quantizers less than 18.

Frame Type Statistics:

I-Frames: 319 (0,91%)
P-Frames: 18634 (53,42%)
B-Frames: 15931 (45,67%)

Frame Quality Statistics:

Q = 18: 18732 (53,70%)
Q = 19: 5200 (14,91%)
Q = 20: 10686 (30,63%)
Q = 21: 91 (0,26%)
Q = 22: 76 (0,22%)
Q = 23: 54 (0,15%)
Q = 24: 39 (0,11%)
Q = 25: 3 (0,01%)
Q = 26: 3 (0,01%)

Minimum Frame Quantizer: 18
Maximum Frame Quantizer: 26

Average I-Frame Quantizer: 18,01
Average P-Frame Quantizer: 18,03
Average B-Frame Quantizer: 19,7

99.24% of the frames have lower quantizers (18,19,20) soo that means very good quality.

Video Track 105 MB H264

Audio Track 16.9 MB AAC

Video and Audio 122 MB H264/AAC/MKV

I got a 122 MB file that use only the necessary bitrate it dont waste useless bitrate on quantizers lower than 18 that our eyes dont see the difference. High quality video and audio with just 122 MB, less MBs to upload and less time to download.
I even got more encoding speed using QPMin 18 because CABAC become more fast when the frame have lower bitrate.
A QP 10 frame have really more bitrate than a frame with QP 18 soo that means really less bitrate on QP 18 soo the CABAC option is more fast on QPMin 18 than the default QPMin 10.

Using QPMin 18 will assure that the video will only use the bitrate that is really needed and using QPMax 24 will assure that the encode will only have the max of 175 MB.
If the anime is slow it will have filesize lower than 175 MB and if the anime is faster the filesize will stay at the maximun of 175 MB because the QPMax 24 will compress more to fit on the 175 MB filesize.

I think that it is a good idea to use 2-Pass encode with QPMin 18 and QPmax 24 soo we can stop making files that waste a lot of bitrate uselessly.
Kurth is offline   Reply With Quote