Depends on the standard you’re working in.
HD videotape runs at different speeds depending on the standard you are using. Running time of HD tapes sold in the U.S. is indicated for 59.94i frame rate. This standard is the “fastest” and will result in the shortest running time.
Let’s see how this works. A 64 minute tape will give you these running times:
HD standard: 59.94i 50i 23.98p
running time: 64 min. 76 min. 80 min.
Not bad, you get more tape for less money. The simple formulas you can use are:
50i RT = nominal RT x 1.19
23.98p RT = nominal RT x 1.25
Above formulas do not apply to DVCPRO HD.