ytdl "http://www.youtube.com/watch?v=_HSylqgVYQI" > myvideo.mp4
2. split video using ffmpeg (higher chance of failure when the video is long, split to <10 min is recommended)
ffmpeg -i source-file.mp4 -ss 0 -t 600 -c copy first-10-min.mp4
export GOOGLE_APPLICATION_CREDENTIALS="KEY_PATH" (ref: https://cloud.google.com/docs/authentication/getting-started)
node index.js "video"
Crop video before ocr to reduce noise (ref: https://video.stackexchange.com/a/4571)