mpv does not support video rotation metadata in OpenCamera-recorded MP4 video

mpv version and platform

$ mpv --version
mpv 0.27.0-270-g0358cca39e (C) 2000-2017 mpv/MPlayer/mplayer2 projects
 built on Mon Oct 23 11:32:08 CEST 2017
ffmpeg library versions:
   libavutil       55.58.100
   libavcodec      57.89.100
   libavformat     57.71.100
   libswscale      4.6.100
   libavfilter     6.82.100
   libswresample   2.7.100
ffmpeg version: 3.3.4

Arch Linux

Reproduction steps

1. Play sample file
2. Notice how it's not rotated correctly
3. Open sample file in gwenview (or look at the generated thumbnail from KDE's thumbnailer)
4. Note how it is correctly rotated -90 degrees there

Expected behavior

mpv shows the video in the proper rotation

Actual behavior

mpv shows the video rotated 90 degree clockwise

Log file

https://0x0.st/sr3T.log

Sample files

https://0x0.st/sr3b.mp4

Additional info:

$ ffprobe VID_20171023_132840.mp4 
ffprobe version 3.3.4 Copyright (c) 2007-2017 the FFmpeg developers
  built with gcc 7.2.0 (GCC)
  configuration: --prefix=/usr --disable-debug --disable-static --disable-stripping --enable-avisynth --enable-avresample --enable-fontconfig --enable-gmp --enable-gnutls --enable-gpl --enable-ladspa --enable-libass --enable-libbluray --enable-libfreetype --enable-libfribidi --enable-libgsm --enable-libiec61883 --enable-libmodplug --enable-libmp3lame --enable-libopencore_amrnb --enable-libopencore_amrwb --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libv4l2 --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libx264 --enable-libx265 --enable-libxcb --enable-libxvid --enable-shared --enable-version3
  libavutil      55. 58.100 / 55. 58.100                                                     
  libavcodec     57. 89.100 / 57. 89.100                                                     
  libavformat    57. 71.100 / 57. 71.100                                                     
  libavdevice    57.  6.100 / 57.  6.100                                                     
  libavfilter     6. 82.100 /  6. 82.100                                                     
  libavresample   3.  5.  0 /  3.  5.  0                                                     
  libswscale      4.  6.100 /  4.  6.100                                                     
  libswresample   2.  7.100 /  2.  7.100                                                     
  libpostproc    54.  5.100 / 54.  5.100                                                     
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'VID_20171023_132840.mp4':                           
  Metadata:                                                                                  
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2017-10-23T11:29:09.000000Z
    com.android.version: 6.0.1
  Duration: 00:00:27.67, start: 0.000000, bitrate: 20280 kb/s
    Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1280x720, 19950 kb/s, SAR 1:1 DAR 16:9, 29.88 fps, 29.92 tbr, 90k tbn, 180k tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : 2017-10-23T11:29:09.000000Z
      handler_name    : VideoHandle
    Side data:
      displaymatrix: rotation of -90.00 degrees
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 95 kb/s (default)
    Metadata:
      creation_time   : 2017-10-23T11:29:09.000000Z
      handler_name    : SoundHandle

Start by reproducing the issue with the linked MP4 sample and inspect its FFmpeg rotation metadata and display matrix alongside the linked log. Trace how mpv handles that metadata during video playback; done means the OpenCamera sample displays with the expected -90-degree rotation.