试图用Python获取ffprobe的输出结果

Question

我试图捕获ffprobe的输出结果。首先，我建我的命令：

>>> print cmd 
['C:\\Program Files\\ffmpeg\\bin\\ffprobe.exe', 'somefile.mov'] 

然后我用check_output抢输出：

>>> import subprocess as sp 
>>> output = sp.check_output(cmd) 
ffprobe version N-66673-gf0d1b3a Copyright (c) 2007-2014 the FFmpeg developers 
    built on Oct 6 2014 22:10:42 with gcc 4.9.1 (GCC) 
    configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable-bzlib --enable-fontconfi 
g --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca -- 
enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --enable-lib 
opencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp --enable-libschroedinge 
r --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvo-aacenc -- 
enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx264 --enable- 
libx265 --enable-libxavs --enable-libxvid --enable-zlib 
    libavutil  54. 9.100/54. 9.100 
    libavcodec  56. 3.101/56. 3.101 
    libavformat 56. 7.104/56. 7.104 
    libavdevice 56. 1.100/56. 1.100 
    libavfilter  5. 1.102/5. 1.102 
    libswscale  3. 1.100/3. 1.100 
    libswresample 1. 1.100/1. 1.100 
    libpostproc 53. 1.100/53. 1.100 
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'somefile.mov': 
    Metadata: 
    major_brand  : qt 
    minor_version : 512 
    compatible_brands: qt 
    encoder   : Lavf56.7.104 
    Duration: 00:20:54.46, start: 0.000000, bitrate: 1734 kb/s 
    Stream #0:0(eng): Video: h264 (Main) (avc1/0x31637661), yuv420p(tv, bt709), 1280x720, 1617 kb/s, 24 fps, 24 tbr, 1 
2288 tbn, 24576 tbc (default) 
    Metadata: 
     handler_name : DataHandler 
    Stream #0:1(eng): Audio: aac (mp4a/0x6134706D), 48000 Hz, stereo, fltp, 113 kb/s (default) 
    Metadata: 
     handler_name : DataHandler 

然而，当我打印输出，我什么也没有：

>>> print output 

我与Popen相同的结果和沟通（）：

>>> output = sp.Popen(cmd, stdout=sp.PIPE) 
>>> output.communicate() 
('', None) 

嗯，我想这不是什么都没有。看起来我有一个空白的字符串回来？

Answer 1

奇怪......我可以用stderr抓住它吗？

>>> output = sp.Popen(cmd, stdout=sp.PIPE, stderr=sp.PIPE) 
>>> output.communicate() 
('', "ffprobe version N-66673-gf0d1b3a Copyright (c) 2007-2014 the FFmpeg developers\r\n built on Oct 6 2014 22:10:42 
with gcc 4.9.1 (GCC)\r\n configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-avisynth --enable- 
bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enable-iconv --enable-libass --enable-libbluray --enable-lib 
bs2b --enable-libcaca --enable-libfreetype --enable-libgme --enable-libgsm --enable-libilbc --enable-libmodplug --enable 
-libmp3lame --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-libopus --enable-librtmp 
--enable-libschroedinger --enable-libsoxr --enable-libspeex --enable-libtheora --enable-libtwolame --enable-libvidstab 
--enable-libvo-aacenc --enable-libvo-amrwbenc --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp -- 
enable-libx264 --enable-libx265 --enable-libxavs --enable-libxvid --enable-zlib\r\n libavutil  54. 9.100/54. 9. 
100\r\n libavcodec  56. 3.101/56. 3.101\r\n libavformat 56. 7.104/56. 7.104\r\n libavdevice 56. 1.1 
00/56. 1.100\r\n libavfilter  5. 1.102/5. 1.102\r\n libswscale  3. 1.100/3. 1.100\r\n libswresamp 
le 1. 1.100/1. 1.100\r\n libpostproc 53. 1.100/53. 1.100\r\nInput #0, mov,mp4,m4a,3gp,3g2,mj2, from 'somefile.mov':\r\n Metadata:\r\n major_brand  : qt \r\n minor_version : 512\r\n 
    compatible_brands: qt \r\n encoder   : Lavf56.7.104\r\n Duration: 00:20:54.46, start: 0.000000, bitrate: 17 
34 kb/s\r\n Stream #0:0(eng): Video: h264 (Main) (avc1/0x31637661), yuv420p(tv, bt709), 1280x720, 1617 kb/s, 24 fps 
, 24 tbr, 12288 tbn, 24576 tbc (default)\r\n Metadata:\r\n  handler_name : DataHandler\r\n Stream #0:1(eng) 
: Audio: aac (mp4a/0x6134706D), 48000 Hz, stereo, fltp, 113 kb/s (default)\r\n Metadata:\r\n  handler_name : 
DataHandler\r\n") 

我想ffprobe的所有输出结果实际上都是通过stderr输入的。