获取视频属性
用ffprobe获取视频分辨率 宽度和高度
ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 video_file.mp4
举例：
# ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 course_1608_video_normalWatermark_477w360h.mp4
480x360
查看视频基本信息
通过：
ffmpeg -i xxx.mp4
即可看到mp4视频的信息，其中包括了字幕的信息：
Stream #0:2(zho): Subtitle: mov_text (tx3g / 0x67337874), 1280x108, 0 kb/s (default)
Metadata:
creation_time : 2018-10-13T03:27:31.000000Z
handler_name : SubtitleHandler
其中：
Stream #0:2：字幕也是一个stream流，index是0:2zho：(应该)表示是中文mov_text：后来才听说，好像指的是Apple Mov Text格式的？
举例1
➜ ffmpeg_edit_subtitle ffmpeg -i CTT_Folge_01_CH_Subs_DefaultZhcnButNotShow.mp4
ffmpeg version 3.4.2 Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.4.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --disable-jack --enable-gpl --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libavresample 3. 7. 0 / 3. 7. 0
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'CTT_Folge_01_CH_Subs_DefaultZhcnButNotShow.mp4':
Metadata:
major_brand : mp42
minor_version : 512
compatible_brands: isomiso2avc1mp41
creation_time : 2018-10-13T03:27:31.000000Z
encoder : HandBrake 1.1.2 2018090500
Duration: 00:26:52.03, start: -0.001333, bitrate: 1762 kb/s
Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p(tv, bt709), 1280x720 [SAR 1:1 DAR 16:9], 1599 kb/s, 25 fps, 25 tbr, 90k tbn, 180k tbc (default)
Metadata:
creation_time : 2018-10-13T03:27:31.000000Z
handler_name : VideoHandler
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 157 kb/s (default)
Metadata:
creation_time : 2018-10-13T03:27:31.000000Z
handler_name : Stereo
Stream #0:2(zho): Subtitle: mov_text (tx3g / 0x67337874), 1280x108, 0 kb/s (default)
Metadata:
creation_time : 2018-10-13T03:27:31.000000Z
handler_name : SubtitleHandler
At least one output file must be specified
看到字幕了：Stream #0:2(zho)
zho应该是中文
且显示已经是default了，即默认是中文字幕（而不是之前的英文字幕）
举例2
ffmpeg -i 1xx-我来保证你们的安全.mp4
ffmpeg version 3.4.2 Copyright (c) 2000-2018 the FFmpeg developers
built with Apple LLVM version 9.0.0 (clang-900.0.39.2)
configuration: --prefix=/usr/local/Cellar/ffmpeg/3.4.2 --enable-shared --enable-pthreads --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --disable-jack --enable-gpl --enable-libmp3lame --enable-libx264 --enable-libxvid --enable-opencl --enable-videotoolbox --disable-lzma
libavutil 55. 78.100 / 55. 78.100
libavcodec 57.107.100 / 57.107.100
libavformat 57. 83.100 / 57. 83.100
libavdevice 57. 10.100 / 57. 10.100
libavfilter 6.107.100 / 6.107.100
libavresample 3. 7. 0 / 3. 7. 0
libswscale 4. 8.100 / 4. 8.100
libswresample 2. 9.100 / 2. 9.100
libpostproc 54. 7.100 / 54. 7.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from '1xxx-我来保证你们的安全.mp4':
Metadata:
major_brand : isom
minor_version : 0
compatible_brands: isomiso2avc1
creation_time : 2018-01-28T05:46:37.000000Z
Duration: 00:01:26.24, start: 0.000000, bitrate: 606 kb/s
Stream #0:0(eng): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 640x360 [SAR 1:1 DAR 16:9], 541 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)
Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 62 kb/s (default)
Metadata:
creation_time : 2018-01-28T05:46:35.000000Z
At least one output file must be specified
中并没有Subtitle的信息
-> 看来这个视频本身就不包含独立的字幕
-> 没法用ffmpeg去提取字幕了