I found an easy way to solve this problem: simply change the code in multi_frame_render.py
reference_imgs = gr.UploadButton(label="Upload Guide Frames", file_types = ['.png','.jpg','.jpeg'], live=True, file_count = "multiple")
to
reference_imgs = gr.File(file_count="directory", label="Upload Guide Frames", show_label=True)
like this:
it works for me!