convert_video2gif function error

[joseph16388]

When I run to :
def convert_video2gif(video_path, output_gif_path, num_samples=16):
p = (
pipe.input('video_path')
.map('video_path', 'video_frames',
ops.video_decode.ffmpeg(sample_type='uniform_temporal_subsample', args={'num_samples': num_samples}))
.output('video_frames')
)
frames = p(video_path).to_list()[0][0]
imgs = [Image.fromarray(frame) for frame in frames]
imgs[0].save(fp=output_gif_path, format='GIF', append_images=imgs[1:], save_all=True, loop=0)

There is an error: 

raise RuntimeError(node.err_msg)
RuntimeError: Node-video-decode/ffmpeg-0 runs failed, error msg: Create video-decode/ffmpeg-0 operator video-decode/ffmpeg:main with args None and kws {'sample_type': 'uniform_temporal_subsample', 'args': {'num_samples': 16}} failed, err: Load operator failed, Traceback (most recent call last):

In this place:
https://github.com/towhee-io/examples/blob/main/video/text_video_retrieval/1_text_video_retrieval_engine.ipynb