I use F4, which is made for MS Windows, but there is also a version for Mac. At the time I downloaded it it was free, now I see that there are various licenses.
Have a look for your self: http://www.audiotranskription.de/english/f4.htm
depending on what your are looking exactly for in video transcription, pls have a look at the open source tools in this area which are: Exmaralda, Sonal, Anvil, ELAN. Praat could also do the job. If you are looking to qualitatively analyse the data after transcription then you should also consider Transana which is mainly a Analysis programm but which also has transcription functionality.