Generally speaking, you can use both verbs to mean the same thing; however, in some countries it is preferred one verb other the other one. What I would say you could think of "mirando" as actively seeing (attentively seeing or concentrating on seeing) something and "viendo" as just seeing without focus on the action. Honestly, I use both verbs when my family members would call me during my leisure time (TV or movie); but I use more the verb "viendo" since "mirando" could also imply a distance between the subject and the action.
(Yo) Estoy viendo la television. ----- No problem about context.
(Yo) Estoy mirando la television. ----- No problem about context but could denote that this is something you are actively doing.
Ella esta viendo la television. ----- No problem about context.
Ella esta mirando la television.----- No problem about context but could denote that this is something you are actively doing.
(Yo) Voy al concierto. ---- I am going to the concert.
(Yo) Estoy en el concierto - I am at the concert.
(Yo) Estoy viendo el concierto de piano ---- I am seeing the piano concert.
(Yo) Estoy mirando el concierto. ---- Means the same thing as with the verb viendo but depending on the frequency of usage of the Verb Mirar in the country, this sentence could imply negative connotation between subject and event; But this is purely due to the perceptions of people using common language and common verbs.
Ella esta viendo a su hijo jugar futbol ---- She is watching her son play soccer.
Ella esta mirando a su hijo jugar futbol ----- Same comment as two examples back.
I could be mistaken but the verb to see a concert would sound a bit weird. I have heard people say more often they are in the concert or they are enjoying the concert. I would be interested to see what other people think, as I would be speaking from the point of view of Venezuelan Spanish. I hope this helps.