Fix "ValueError" when Parsing Data && add recginzing "ffmpeg.exe" on Windows OS

[iWangJiaxiang]

My PR has following changes:

• Fix JSONDecodeError #126 ValueError issue.

except (ValueError, IndexError):   

• Add recginzing "ffmpeg.exe" on Windows OS. Now you do not need any operation about ffmpeg.exe on Windows. The codes are as fsollowed:

def ffmpeg_check():
    """
    Return the ffmpeg executable name. "null" returned when no executable exsits.
    """
    if which("ffmpeg"):
        return "ffmpeg"
    elif which("ffmpeg.exe"):
        return "ffmpeg.exe"
    else:
        return None

Enjoy! :D

[BingLingGroup]

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