FFMPEG 旋转元数据有时顺时针，有时逆时针

Question

我有两台不同的机器，安装了两个不同版本的 ffmpeg。我正在尝试使用 -metadata:s:v:0 rotate=$theta 将视频的显示矩阵设置为具有旋转值筛选。

在 #1 机器上

FFMPEG 版本:

$ ffmpeg -version
ffmpeg version 4.2.1 Copyright (c) 2000-2019 the FFmpeg developers
built with Apple clang version 11.0.0 (clang-1100.0.33.8)
configuration: --prefix=/usr/local/Cellar/ffmpeg/4.2.1_2 --enable-shared --enable-pthreads --enable-version3 --enable-avresample --cc=clang --host-cflags='-I/Library/Java/JavaVirtualMachines/adoptopenjdk-13.jdk/Contents/Home/include -I/Library/Java/JavaVirtualMachines/adoptopenjdk-13.jdk/Contents/Home/include/darwin -fno-stack-check' --host-ldflags= --enable-ffplay --enable-gnutls --enable-gpl --enable-libaom --enable-libbluray --enable-libmp3lame --enable-libopus --enable-librubberband --enable-libsnappy --enable-libtesseract --enable-libtheora --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libx265 --enable-libxvid --enable-lzma --enable-libfontconfig --enable-libfreetype --enable-frei0r --enable-libass --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-librtmp --enable-libspeex --enable-libsoxr --enable-videotoolbox --disable-libjack --disable-indev=jack
libavutil      56. 31.100 / 56. 31.100
libavcodec     58. 54.100 / 58. 54.100
libavformat    58. 29.100 / 58. 29.100
libavdevice    58.  8.100 / 58.  8.100
libavfilter     7. 57.100 /  7. 57.100
libavresample   4.  0.  0 /  4.  0.  0
libswscale      5.  5.100 /  5.  5.100
libswresample   3.  5.100 /  3.  5.100
libpostproc    55.  5.100 / 55.  5.100

命令:

$ ffmpeg -i 0_degree_rotation.mp4 -vcodec copy -metadata:s:v:0 rotate=90 /tmp/out.mp4

输出视频的元数据:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/tmp/out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : "Camio"
    encoder         : Lavf58.29.100
  Duration: 00:00:10.71, start: 0.000000, bitrate: 2241 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 2239 kb/s, 14.94 fps, 14.94 tbr, 14941 tbn, 29.88 tbc (default)
    Metadata:
      rotate          : 270
      handler_name    : VideoHandler
    Side data:
      displaymatrix: rotation of 90.00 degrees

在机器 #2

FFMPEG 版本:

ffmpeg version 2.8.15-0ubuntu0.16.04.1 Copyright (c) 2000-2018 the FFmpeg developers
built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.10) 20160609
configuration: --prefix=/usr --extra-version=0ubuntu0.16.04.1 --build-suffix=-ffmpeg --toolchain=hardened --libdir=/usr/lib/x86_64-linux-gnu --incdir=/usr/include/x86_64-linux-gnu --cc=cc --cxx=g++ --enable-gpl --enable-shared --disable-stripping --disable-decoder=libopenjpeg --disable-decoder=libschroedinger --enable-avresample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libmodplug --enable-libmp3lame --enable-libopenjpeg --enable-libopus --enable-libpulse --enable-librtmp --enable-libschroedinger --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxvid --enable-libzvbi --enable-openal --enable-opengl --enable-x11grab --enable-libdc1394 --enable-libiec61883 --enable-libzmq --enable-frei0r --enable-libx264 --enable-libopencv
libavutil      54. 31.100 / 54. 31.100
libavcodec     56. 60.100 / 56. 60.100
libavformat    56. 40.101 / 56. 40.101
libavdevice    56.  4.100 / 56.  4.100
libavfilter     5. 40.101 /  5. 40.101
libavresample   2.  1.  0 /  2.  1.  0
libswscale      3.  1.101 /  3.  1.101
libswresample   1.  2.101 /  1.  2.101
libpostproc    53.  3.100 / 53.  3.100

命令:

$ ffmpeg -i /tmp/0_degree_rotation.mp4 -vcodec copy -metadata:s:v:0 rotate=90 /tmp/out.mp4

输出视频的元数据

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/tmp/out.mp4':
  Metadata:
    major_brand     : isom
    minor_version   : 512
    compatible_brands: isomiso2avc1mp41
    title           : "Camio"
    encoder         : Lavf56.40.101
  Duration: 00:00:10.71, start: 0.000000, bitrate: 2241 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 1920x1080 [SAR 1:1 DAR 16:9], 2239 kb/s, 14.94 fps, 14.94 tbr, 14941 tbn, 29.88 tbc (default)
    Metadata:
      rotate          : 90
      handler_name    : VideoHandler
    Side data:
      displaymatrix: rotation of -90.00 degrees

为什么相同的命令会在一个版本的 ffmpeg 中产生 +90 度的旋转，而在不同的版本中产生 -90 度的旋转？

Answer 1

在 3.3 版中更改了旋转 API。新 API 在内部使用不同的数据结构来表示和存储旋转(和翻转)值，其方向与旧 API 相反。一般来说，2.8是一个很老的版本，你应该把所有的机器都升级到4.2。