When --overwrite is enabled, the final movie can contain unrequested frames

[Sbozzolo]

At the moment, ffmpeg uses a glob pattern to file which frames to include. This can lead to glitches when the --overwrite flag is enable and files that match that glob pattern were already present in the directory (but not overwritten).

Consider the case the output directory has files 0.png, 1.png, 2.png, and, with our choice, we only produce and overwrite only 1.png (e.g., by setting --frames-every). The final movie will contains frames it shouldn't.

A possible bug fix is to avoid using glob patterns but provide the list of the input files explicitly.