Export animation to avi

Question

I'm trying to export an animation but the output is always $Failed with the error message:

Export: The value Automatic specified for the option AudioEncoding is invalid

Here is my code:

Import["C:\\Users\\USER\\AppData\\Roaming\\Mathematica\\ffmpeg-mathematica-master\\FFmpeg.m"];
m1 = Manipulate[Plot[Sin[x (1 + a x)], {x, 0, 6}], {a, 0, 2}]
Export["test.avi", m1]

I think is valid to mention that I installed FFmpeg from an external source following Yogesh Patil's answer to this question.. Also, when I verify the FFmpeg version in my command prompt using ffmpeg - version, this message appears:

    [NULL @ 000001fce09c9a80] Unable to find a suitable output format for 'pipe:'
pipe:: Invalid argument

I'm not sure if that affects what I'm trying to do in Mathematica