ffmepg

我想给manim提供检测ffmpeg的程序
`import subprocess

cmd = "ffmpeg -version"
cmd_return = subprocess.getoutput(cmd)
if cmd_return == "'ffmpeg' 不是内部或外部命令，也不是可运行的程序或批处理文件。":
raise Exception("FFMPEG not found")
else:
print("found FFMPEG")`

Look for where manim checks for external dependencies, likely in a setup or configuration module. The issue suggests using subprocess to run 'ffmpeg -version' and handling the output. Check existing error handling for missing ffmpeg to integrate this detection cleanly. Test by simulating missing and present ffmpeg to ensure the exception is raised appropriately.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.