Convert au to ffv1

Download and install the latest version of Filestar.
Right click on one or more Au file(s) on your desktop and select Convert with Filestar.
Type convert to ffv1 in the search box.
Press Convert.

What is the difference between .au and .ffv1?

Name: Audacity Audio File; FFV1 (Lossless Video)
Extension: .au; .ffv1
Format: Binary; Binary
Category: Audio; Video
Developer: Audacity
Description: Audio file created by Audacity, a free, cross platform audio editor; uses a proprietary format that can only be opened by Audacity; saved as one of multiple audio data files for an Audacity project (.AUD).
MIME Type: audio/basic; video/x-matroska
Sample: sample.au
Wikipedia: .au on Wikipedia; .ffv1 on Wikipedia