You can use ffmpeg to combine one or more images with an audio track.
- Works Offline
- Cross Platform Linux & Windows
- Free, Gratis & Open Source
- Command line &/or scriptable
- Huge range of possible input & output formats.
Example from the wiki:
ffmpeg -loop 1 -i img.jpg -i audio.wav -c:v libx264 -c:a aac -strict experimental -b:a 192k -shortest out.mp4