<div dir="ltr"><div><div>Hello,<br><br></div>Without the keyint argument, the default keyframe interval reverts to 250, and the encoder will try to insert I-frames only closer to this value. With --keyint 50, the encoder will try to insert GOP frames closer to 50, and thats what the GOP size would roughly be. <br><br></div>At the points where you expected a scene change / I frame, you might find that the P-frames are significantly larger, but it's likely the encoder didnt deem it necessary to insert an I-frame. <br><div><br><br></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sat, Aug 22, 2015 at 4:51 AM, Roshantha Mendis <span dir="ltr"><<a href="mailto:hrm506@york.ac.uk" target="_blank">hrm506@york.ac.uk</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="ltr"><div><div>Hi,<br>
<br>
I am trying to investigate GoP size changes based on scene changes in video.<br>
<br>
i've used x265 to encode a y4m (raw) file to hevc bitstream. A standard action fight scene : high moving, fast paced, 2-3 mins). So I was hoping to get
highly varying scene changes. link : <br><a href="https://www.youtube.com/watch?v=gQEfEeBR3-M" target="_blank">https://www.youtube.com/watch?v=gQEfEeBR3-M</a><br>
<br>
I used this command:<br>
<br>
./x265 --input ../../../../ffmpeg_work/vids/originals/FightScene.y4m -F 0
-o FightScene_x265.bin --csv FightScene_x265.csv --csv-log-level 2<br>
<br>
// -- more info --<br>
<br>
y4m [info]: 312x176 fps 25/1 i420p8 frames 0 - 5104 of 5105<br>
raw [info]: output file: FightScene_x265.bin<br>
x265 [info]: HEVC encoder version 1.7+431-f63273fa3137<br>
x265 [info]: build info [Linux][GCC 4.8.4][64 bit] 8bit<br>
x265 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX AVX2 FMA3 LZCNT BMI2<br>
x265 [info]: Main profile, Level-2 (Main tier)<br>
x265 [info]: Thread pool created using 4 threads<br>
x265 [info]: frame threads / pool features : 2 / wpp(3 rows)<br>
x265 [info]: Coding QT: max CU size, min CU size : 64 / 8<br>
x265 [info]: Residual QT: max TU size, max depth : 32 / 1 inter / 1 intra<br>
x265 [info]: ME / range / subpel / merge : hex / 57 / 2 / 2<br>
x265 [info]: Keyframe min / max / scenecut : 25 / 250 / 40<br>
x265 [info]: Lookahead / bframes / badapt : 20 / 4 / 2<br>
x265 [info]: b-pyramid / weightp / weightb : 1 / 1 / 0<br>
x265 [info]: References / ref-limit cu / depth : 3 / 0 / 0<br>
x265 [info]: AQ: mode / str / qg-size / cu-tree : 1 / 1.0 / 32 / 1<br>
x265 [info]: Rate Control / qCompress : CRF-28.0 / 0.60<br>
x265 [info]: tools: rd=3 psy-rd=0.30 signhide tmvp strong-intra-smoothing<br>
x265 [info]: tools: deblock sao<br>
x265 [info]: frame I: 2, Avg QP:27.50 kb/s: 919.70<br>
x265 [info]: frame P: 82, Avg QP:29.56 kb/s: 170.33<br>
x265 [info]: frame B: 195, Avg QP:35.66 kb/s: 27.40<br>
x265 [info]: Weighted P-Frames: Y:1.2% UV:1.2%<br>
x265 [info]: consecutive B-frames: 9.3% 18.6% 12.8% 44.2% 15.1%<br>
<br>
<br>
// ---------<br>
<br>
<br>
So very basic, using only the defaults.<br>
<br>
I then investgate the csv file, and check the I-SLICE to I-SLICE frame gap (I assume I-Slice --> I-Slice is a GOP)<br>
<br>
They all seem around 246 to 252 frames per GoP. I was hoping to get drastic GoP changes : e.g. GoP sizes 25, 36, 100 .. 250 etc.<br>
<br>
Any thoughts why the difference are so small ?<br><br></div>I even tried setting the following flags to high values : <code></code><br><br>--scenecut 100 --keyint 240 --min-keyint 2 <br><br>but the still the gop size remained around 238-242 .. not much fluctuation. <br><br><br></div><div>Please can someone advice why ?<br><br><br></div><div><br>Many thanks
<br><span class="HOEnZb"><font color="#888888"><br clear="all"><br>-- <br><div>Rosh Mendis<div>Research Student - EngD in LSCITS</div><div>Dept. of Computer Science</div><div>University of York<br><br><span><font color="#888888">Disclaimer: <a href="http://www.york.ac.uk/docs/disclaimer/email.htm" target="_blank">http://www.york.ac.uk/docs/disclaimer/email.htm</a></font></span><br></div></div>
</font></span></div></div>
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<br></blockquote></div><br></div>