If you recorded the file to FLV, once you followed the steps to
convert it to an MP4, the audio would have been fixed (from my tests at least). However, since Windows Media Player was able to play the file in the first place, I know you recorded straight to MP4, which is not a good idea because MP4s can corrupt quite easily, causing you to lose your recording. If you still want to avoid having to remux files, and don't mind losing some files, go into Settings > Encoding, and change your audio encoder to "MP3". This way future files' audio should be viewable by Windows Movie Maker immediately after recording if you still record straight into an MP4 container.
In your and Nmoleo's cases, however, the solution to save your current recording won't be that simple.
On the guide up that I linked to near the beginning, I'll have you follow method 2, but I'm only going to have the audio track converted to MP3, which Windows Movie Maker / Windows Media Player likes much better. Please make a copy of the original recording in case this doesn't work.
After downloading and extracting one of the
static builds of FFMPEG (you'll need
7-zip to open it, but it's good to have that anyways, better than WinRar, which is in every single way inferior and also not free), go into the extracted folder and run ff-prompt.bat.
Type:
Code:
ffmpeg -i "C:\path\to\video.mp4" -vcodec copy -acodec mp3 -copyts "C:\wherever\you\want\the\output.mp4"
obviously replacing "C:\path\to\video.mp4" with the name and location of the video you want to edit with WMM, encased in quotation marks for safety. The output should also be named something different than the original video (or be put in a different folder), so you don't overwrite it.
I can't test this out myself, since Win10 doesn't have Movie Maker and on top of that I can't seem to get the sound to not play, but I'm fairly sure this will work. I've tried to make this as detailed as possible, but if you're confused about something, feel free to ask for clarification.
