Python 子进程调用 ffmpeg（命令行）
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subprocess call ffmpeg (command line)
提问by user3295674
I have been incorporating subprocess calls in my program. I have had no issues with subprocess calls for other commands, but I am having trouble getting the command line input
我一直在我的程序中加入子进程调用。我对其他命令的子进程调用没有任何问题，但在获取命令行输入时遇到问题
ffmpeg -r 10 -i frame%03d.png -r ntsc movie.mpg
To work inside a subprocess.call()
在 subprocess.call() 中工作
I tried the following with no success:
我尝试了以下但没有成功：
subprocess.call('ffmpeg -r 10 -i %s frame%03.d.png - r ntsc movie.mpg')
Any thoughts? Do I separate out different commands, do I specify string, integer etc. with %s, %d?
有什么想法吗？难道我分离出不同的命令，我指定字符串，整数等用%s，%d？
采纳答案by user3295674
I found this alternative, simple, answer to also work.
我发现这个替代的，简单的，答案也有效。
subprocess.call('ffmpeg -r 10 -i frame%03d.png -r ntsc '+str(out_movie), shell=True)
回答by tdelaney
When you use subprocess, your command must either be a string that looks exactly like what you would type on the command line (and you set shell=True), or a list where each command is an item in the list (and you take the default shell=False). In either case, you have to deal with the variable part of the string. For instance, the operating system has no idea what "%03d" is, you have to fill it in.
当您使用 subprocess 时，您的命令必须是一个与您在命令行上键入的内容完全相同的字符串（并且您设置了 shell=True），或者是一个列表，其中每个命令都是列表中的一个项目（并且您将默认外壳=假）。无论哪种情况，您都必须处理字符串的可变部分。例如，操作系统不知道“%03d”是什么，你必须填写它。
I can't tell from your question exactly what the parameters are, but lets assume you want to convert frame 3, it would look something like this in a string:
我无法从你的问题中确切地说出参数是什么，但假设你想转换第 3 帧，它在字符串中看起来像这样：
my_frame = 3
subprocess.call(
'ffmpeg -r 10 -i frame%03d.png -r ntsc movie%03d.mpg' % (my_frame, my_frame),
shell=True)
Its kinda subtle in this example, but that's risky. Suppose these things were in a directory whose name name had spaces (e.g., ./My Movies/Scary Movie). The shell would be confused by those spaces.
在这个例子中它有点微妙，但这是有风险的。假设这些东西在一个名字有空格的目录中（例如，./My Movies/Scary Movie）。外壳会被这些空间混淆。
So, you can put it into a list and avoid the problem
所以，你可以把它放在一个列表中，避免这个问题
my_frame = 3
subprocess.call(['ffmpeg', '-r', '10', '-i', 'frame%03d.png' % my_frame,
['-r', 'ntsc', 'movie%03d.mpg' % my_frame])
More typing, but safer.
更多打字，但更安全。
回答by PM 2Ring
'ffmpeg -r 10 -i frame%03d.png -r ntsc movie.mpg'should be fine. OTOH, If you don't need the power of frame%03d.png, frame*.pngis a bit simpler.
'ffmpeg -r 10 -i frame%03d.png -r ntsc movie.mpg'应该没事。OTOH，如果你不需要的功率frame%03d.png，frame*.png是有点简单。
If you want to "see the syntax for it if I replace 'movie.mpg' with a variable name", it looks something like this:
如果你想“如果我用变量名替换 'movie.mpg' 来查看它的语法”，它看起来像这样：
cmd = 'ffmpeg -r 10 -i "frame%%03d.png" -r ntsc "%s"' % moviename
cmd = 'ffmpeg -r 10 -i "frame%%03d.png" -r ntsc "%s"' % moviename
We need to escape the %with an extra %to hide it from Python's % substitution machinery. I've also added double quotes ", to cope with the issues that tdelaney mentioned.
我们需要%用一个额外的方法来逃避%Python 的 % 替换机制。我还添加了双引号"，以解决 tdelaney 提到的问题。
回答by jfs
import shlex
import pipes
from subprocess import check_call
command = 'ffmpeg -r 10 -i frame%03d.png -r ntsc ' + pipes.quote(out_movie)
check_call(shlex.split(command))
