从shell运行的c# – ffmpeg运行正常,但是从.NET内部调用时则不行

我试图在C#程序中使用ffmpeg(在 Windows上使用Cygwin编译),通过使用Process类来生成ffmpeg实例.但是,我遇到了一个相当奇怪的错误,没有多大意义.

当我直接从shell运行ffmpeg时(无论是Cygwin的bash,PowerShell,cmd),ffmpeg可以正确解码和重新编码文件而不会出现任何问题：

PS C:\audio> ffmpeg -i .\sound1.wav -acodec libvorbis -f ogg abc.ogg
ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  built on Apr  8 2013 15:10:40 with gcc 4.5.3 (GCC)
  configuration: --disable-encoder=vorbis --enable-libvorbis
  libavutil      52. 18.100 / 52. 18.100
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.104 / 54. 63.104
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 42.103 /  3. 42.103
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
[wav @ 0x800538a0] max_analyze_duration 5000000 reached at 5015510 microseconds
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0,wav,from '.\sound1.wav':
  Metadata:
    encoder         : Lavf54.63.104
  Duration: 00:00:05.76,bitrate: 1411 kb/s
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001),44100 Hz,stereo,s16,1411 kb/s
Output #0,ogg,to 'abc.ogg':
  Metadata:
    encoder         : Lavf54.63.104
    Stream #0:0: Audio: vorbis,fltp
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le -> libvorbis)
Press [q] to stop,[?] for help
size=      55kB time=00:00:05.74 bitrate=  78.5kbits/s
video:0kB audio:51kB subtitle:0 global headers:4kB muxing overhead 0.817473%

文件播放正常,我可以编码为WAV或我喜欢的任何其他格式.但是,当我使用以下代码从C#调用ffmpeg时：

string tempfile = Path.GetTempFileName();
FileStream tempfilestr = File.OpenWrite(tempfile);
input.CopyTo(tempfilestr);

ProcessStartInfo pstart = new ProcessStartInfo("ffmpeg",string.Format("-i \"{0}\" -v verbose -y -f wav -",tempfile));
pstart.CreateNoWindow = true;
pstart.ErrorDialog = false;
pstart.RedirectStandardOutput = true;
pstart.RedirectStandardError = true;
pstart.UseShellExecute = false;


Process proc = new Process();
proc.StartInfo = pstart;
proc.Start();
StreamReader stdout = proc.StandardOutput;
StreamReader stderr = proc.StandardError;

outtempfilestr = File.OpenRead(outtempfile);
MemoryStream output = new MemoryStream();

stdout.BaseStream.CopyTo(output);

try {
    proc.Kill();
}
catch(InvalidOperationException) { }
catch(Win32Exception) { }

File.Delete(tempfile);

return output.ToArray();

这会在输出中随机产生错误：

ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  built on Apr  8 2013 15:10:40 with gcc 4.5.3 (GCC)
  configuration: --disable-encoder=vorbis --enable-libvorbis
  libavutil      52. 18.100 / 52. 18.100
  libavcodec     54. 92.100 / 54. 92.100
  libavformat    54. 63.104 / 54. 63.104
  libavdevice    54.  3.103 / 54.  3.103
  libavfilter     3. 42.103 /  3. 42.103
  libswscale      2.  2.100 /  2.  2.100
  libswresample   0. 17.102 /  0. 17.102
[wav @ 0x80053860] parser not found for codec pcm_s16le,packets or times may be invalid.
    Last message repeated 1 times
[wav @ 0x80053860] max_analyze_duration 5000000 reached at 5015510 microseconds
Guessed Channel Layout for  Input Stream #0.0 : stereo
Input #0,from 'C:\Users\Bevin\AppData\Local\Temp\tmp1CCE.tmp':
  Duration: 00:00:05.20,1411 kb/s
[graph 0 input from stream 0:0 @ 0x8011f320] tb:1/44100 samplefmt:s16 samplerate:44100 chlayout:0x3
Output #0,to 'pipe:':
  Metadata:
    ISFT            : Lavf54.63.104
    Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001),1411 kb/s
Stream mapping:
  Stream #0:0 -> #0:0 (pcm_s16le -> pcm_s16le)
Press [q] to stop,[?] for help
Multiple frames in a packet from stream 0
[pcm_s16le @ 0x8005c160] Invalid PCM packet,data has size 3 but at least a size of 4 was expected
Error while decoding stream #0:0: Invalid data found when processing input
No more output streams to write to,finishing.
size=     896kB time=00:00:05.20 bitrate=1411.3kbits/s    
video:0kB audio:896kB subtitle:0 global headers:0kB muxing overhead 0.008719%

请注意,并非总是会发生这些错误.有时它们会发生在某些文件中,有时却不会发生.我尝试过流重定向和临时文件的各种组合,但它们都不起作用.我还验证了临时文件的完整性,并且全部检查出来.我甚至在删除之前提取了临时文件,并在shell中解密它而没有任何障碍.

有任何想法吗？

编辑：我已经尝试从运行C#的shell脚本运行ffmpeg.它给出了同样的问题.通过MinGW编译ffmpeg也会产生同样的问题.

这是因为你传递参数的方式.做这个：

Process process = new Process();
process.StartInfo.RedirectStandardOutput = true;
process.StartInfo.RedirectStandardError = true;
process.StartInfo.FileName = Path.GetDirectoryName(System.Diagnostics.Process.GetCurrentProcess().MainModule.FileName) +
                        @"\bin\ffmpeg.exe";

process.StartInfo.Arguments = "-i .\sound1.wav -acodec libvorbis -f ogg abc.ogg";


process.StartInfo.UseShellExecute = false;
process.StartInfo.CreateNoWindow = true;
process.Start();

这很完美.