Hello,
When training in Tai Chi, a video can be a good BACK UP source to a quality instructor but can not replace one. There are too many nuances to the training that individuals can not see within themselves. Posture, alignment, relaxation of muscles, breathing even smiling that you really need a qualified instructor to guide you through.
I have been training and teaching for over 25 years and have yet to meet an individual that can tell (at first) that they are tense on the shoulders.
If you are interested in Tai Chi look for an instructor that you feel comfortable with. Observe his/her classes, talk to his/her senior students and determine if this is a path for you. Please remember that Tai Chi only LOOKS easy...