Only first few words are correct in NLP Model

Hi! I am doing a video captioning task using LSTM-RNN encoder-decoder architecture. I notice that after training for few thousands of epochs, the output I get from each video make sense only for the first three words. From 4th word onward, it does not sound like human language to me.


Any suggestion to solve this?

architecture captioning decoder deeplearning encoder encoder-decoder human language lstm nlp nlp model rnn sense sound training video word words