ffmpeg：如何自动确定帧速率？

Question

我使用这个简单的脚本将视频转换为图像ffmpeg，但帧速率是固定的，如何自动确定？

FRAME_RATE="30"
SEPARATOR='/'


VIDEO_PATH=$1

VIDEO_BASE_DIR=`dirname $1`
FRAMES_DIR=$VIDEO_BASE_DIR$SEPARATOR"Frames"
rm -rf $FRAMES_DIR
mkdir $FRAMES_DIR

#Convert video to images
./ffmpeg -r $FRAME_RATE -i $VIDEO_PATH $FRAMES_DIR$SEPARATOR"image%d.png"

更新：

通过ffprobe我检查我的第一个视频帧速率是 30。即使我降低帧速率，结果也是相同的（产生 339 帧），所以-r选项不起作用或以其他方式工作？

这些命令给出相同的结果：

./ffmpeg -r 10 -i $VIDEO_PATH $FRAMES_DIR$SEPARATOR"image%d"$EXTENSION
./ffmpeg -r 30 -i $VIDEO_PATH $FRAMES_DIR$SEPARATOR"image%d"$EXTENSION
./ffmpeg -i $VIDEO_PATH $FRAMES_DIR$SEPARATOR"image%d"$EXTENSION

输出：

ffmpeg version N-63893-gc69defd Copyright (c) 2000-2014 the FFmpeg developers
  built on Jul 16 2014 05:38:01 with gcc 4.6 (Debian 4.6.3-1)
  configuration: --prefix=/root/ffmpeg-static/64bit --extra-cflags='-I/root/ffmpeg-static/64bit/include -static' --extra-ldflags='-L/root/ffmpeg-static/64bit/lib -static' --extra-libs='-lxml2 -lexpat -lfreetype' --enable-static --disable-shared --disable-ffserver --disable-doc --enable-bzlib --enable-zlib --enable-postproc --enable-runtime-cpudetect --enable-libx264 --enable-gpl --enable-libtheora --enable-libvorbis --enable-libmp3lame --enable-gray --enable-libass --enable-libfreetype --enable-libopenjpeg --enable-libspeex --enable-libvo-aacenc --enable-libvo-amrwbenc --enable-version3 --enable-libvpx
  libavutil      52. 89.100 / 52. 89.100
  libavcodec     55. 66.101 / 55. 66.101
  libavformat    55. 43.100 / 55. 43.100
  libavdevice    55. 13.101 / 55. 13.101
  libavfilter     4.  8.100 /  4.  8.100
  libswscale      2.  6.100 /  2.  6.100
  libswresample   0. 19.100 /  0. 19.100
  libpostproc    52.  3.100 / 52.  3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '/home/user/myvideo1.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    creation_time   : 2016-01-16 05:30:03
  Duration: 00:00:11.33, start: 0.000000, bitrate: 4659 kb/s
    Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x480, 4539 kb/s, SAR 65536:65536 DAR 4:3, 30 fps, 30 tbr, 90k tbn, 180k tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : 2016-01-16 05:30:03
      handler_name    : VideoHandle
    Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 127 kb/s (default)
    Metadata:
      creation_time   : 2016-01-16 05:30:03
      handler_name    : SoundHandle
Output #0, image2, to '/home/user/Frames/image%d.png':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: isommp42
    encoder         : Lavf55.43.100
    Stream #0:0(eng): Video: png, rgb24, 640x480 [SAR 1:1 DAR 4:3], q=2-31, 200 kb/s, 30 fps, 90k tbn, 30 tbc (default)
    Metadata:
      rotate          : 90
      creation_time   : 2016-01-12 05:38:03
      handler_name    : VideoHandle
      encoder         : Lavc55.66.101 png
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> png (png))
Press [q] to stop, [?] for help
frame=  339 fps= 68 q=0.0 Lsize=N/A time=00:00:11.30 bitrate=N/A    
video:195852kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown

Answer 1

ffprobe -v 0 -of compact=p=0 -select_streams 0 \
-show_entries stream=r_frame_rate 'The Master (2012).mp4'

结果：

r_frame_rate=24000/1001

Answer 2

您可以使用ffprobe和awk为您获取 fps：

ffprobe -show_streams "video" 2>&1 | \ 
    grep fps | \
    awk '{split($0,a,"fps")}END{print a[1]}' | \
    awk '{print $NF}'

前段时间我写了一篇关于从视频生成 ffmpeg 预览的文章，这可能与您想要做的类似。我必须计算视频中的总帧数：

请参阅https://www.binpress.com/tutorial/how-to-generate-video-previews-with-ffmpeg/138