Word:
1.  name: P01_25_19_2._color.mp4
    P01: 1, signer ID (person)
    25_19: (25-1)*20+19=499, label ID
    2: 2, the second time performing the sign

2.  experiment setting:
    split: 
        train set: signer ID, [0, 1, ..., 34, 35]
        test set: signer ID, [36, 37, ... ,48, 49]