[FFmpeg-trac] #3947(documentation:open): Inconsistent and confusing setting of refs with libx264

[FFmpeg]

#3947: Inconsistent and confusing setting of refs with libx264
-------------------------------------+-------------------------------------
             Reporter:               |                    Owner:
  francois.visagie@…                 |                   Status:  open
                 Type:  defect       |                Component:
             Priority:  minor        |  documentation
              Version:  git-master   |               Resolution:
             Keywords:  libx264      |               Blocked By:
             Blocking:               |  Reproduced by developer:  1
Analyzed by developer:  0            |
-------------------------------------+-------------------------------------

Comment (by francois.visagie@…):

 Unfortunately I can confirm that there is also a software bug, in addition
 to a documentation error. Let's restate the information from
 [https://trac.ffmpeg.org/ticket/3947#comment:2 comment 2]:

 1. When '-x264opts level=x.y' is used, ffmpeg does not correctly set
 reference frames for the specified level (shown in original report above).
 2. However, when --level is used with x264, it DOES correctly set
 reference frames for the specified level:


 {{{
 C:\Users\fvisagie\Videos\Home Videos\Testing\x264>h264levl 720 576 25
 1500000

 h264levl v1.1 (c) F. Visagie 2014/10/31

 level=3
 maxref=5
 x264maxref=5
 }}}

 {{{
 C:\Users\fvisagie\Videos\Home Videos\Testing\x264>x264 --preset veryslow
 --bitrate 1500 --level 3 -o zzz.m4v inprogressive.mpg
 [mpeg @ 003e29c0] max_analyze_duration 5000000 reached
 lavf [info]: 720x576p 64:45 @ 25/1 fps (vfr)
 x264 [info]: using SAR=64/45
 x264 [info]: using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX
 x264 [info]: profile High, level 3.0
 x264 [info]: frame I:15    Avg QP:25.41  size: 45805
 x264 [info]: frame P:473   Avg QP:30.64  size: 12431
 x264 [info]: frame B:1012  Avg QP:34.26  size:  4176
 x264 [info]: consecutive B-frames:  3.9%  4.1% 64.0%  4.5%  5.0% 18.4%
 0.0%  0.0%  0.0%
 x264 [info]: mb I  I16..4:  3.6% 87.1%  9.3%
 x264 [info]: mb P  I16..4:  3.2% 19.9%  1.6%  P16..4: 41.2% 15.1%  8.9%
 0.2%  0.0%    skip: 9.9%
 x264 [info]: mb B  I16..4:  0.6%  3.0%  0.2%  B16..8: 42.4% 10.0%  2.0%
 direct: 3.1%  skip:38.8%  L0:38.0% L1:51.3% BI:10.7%
 x264 [info]: final ratefactor: 25.75
 x264 [info]: 8x8 transform intra:81.2% inter:82.2%
 x264 [info]: direct mvs  spatial:99.6% temporal:0.4%
 x264 [info]: coded y,uvDC,uvAC intra: 69.5% 64.3% 22.2% inter: 19.9% 13.5%
 1.2%
 x264 [info]: i16 v,h,dc,p: 29% 26%  8% 36%
 x264 [info]: i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 16% 10%  5%  7% 11% 15% 12%
 12% 12%
 x264 [info]: i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 22% 10%  4%  7% 12% 16% 11%
 10%  9%
 x264 [info]: i8c dc,h,v,p: 34% 24% 23% 19%
 x264 [info]: Weighted P-Frames: Y:1.1% UV:0.4%
 x264 [info]: ref P L0: 58.5% 20.4% 12.8%  3.2%  3.0%  2.0%  0.1%
 x264 [info]: ref B L0: 90.1%  6.9%  2.2%  0.8%
 x264 [info]: ref B L1: 96.2%  3.8%
 x264 [info]: kb/s:1441.07

 encoded 1500 frames, 11.38 fps, 1441.07 kb/s
 }}}

 Unfortunately I do not know how to show encoder settings or number of
 reference frames in the output file with ffprobe.
 MediaInfo output:

 {{{
 General
 Complete name                            : C:\Users\fvisagie\Videos\Home
 Videos\Testing\x264\zzz.m4v
 Format                                   : AVC
 Format/Info                              : Advanced Video Codec
 File size                                : 10.3 MiB

 Video
 Format                                   : AVC
 Format/Info                              : Advanced Video Codec
 Format profile                           : High at L3.0
 Format settings, CABAC                   : Yes
 Format settings, ReFrames                : 5 frames
 Bit rate                                 : 1 500 Kbps
 Width                                    : 720 pixels
 Height                                   : 576 pixels
 Display aspect ratio                     : 16:9
 Frame rate mode                          : Variable
 Standard                                 : PAL
 Color space                              : YUV
 Chroma subsampling                       : 4:2:0
 Bit depth                                : 8 bits
 Scan type                                : Progressive
 Writing library                          : x264 core 142 r2479 dd79a61
 Encoding settings                        : cabac=1 / ref=5 / deblock=1:0:0
 / analyse=0x3:0x133 / me=umh / subme=10 / psy=1 / psy_rd=1.00:0.00 /
 mixed_ref=1 / me_range=24 / chroma_me=1 / trellis=2 / 8x8dct=1 / cqm=0 /
 deadzone=21,11 / fast_pskip=1 / chroma_qp_offset=-2 / threads=6 /
 lookahead_threads=1 / sliced_threads=0 / nr=0 / decimate=1 / interlaced=0
 / bluray_compat=0 / constrained_intra=0 / bframes=8 / b_pyramid=2 /
 b_adapt=2 / b_bias=0 / direct=3 / weightb=1 / open_gop=0 / weightp=2 /
 keyint=250 / keyint_min=25 / scenecut=40 / intra_refresh=0 /
 rc_lookahead=60 / rc=abr / mbtree=1 / bitrate=1500 / ratetol=1.0 /
 qcomp=0.60 / qpmin=0 / qpmax=69 / qpstep=4 / ip_ratio=1.40 / aq=1:1.00
 }}}

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Ticket URL: <https://trac.ffmpeg.org/ticket/3947#comment:6>
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