You take the total number of parts.
OK...if you mean the ratio of commercials/broadcasts it's 1:3, if you mean the ratio of commercials/total time, it's 1:4 capiche? Perhaps this next example will clarify a bit further: if the ratio of men to women in some group is 1:1, then 50% are men and 50% are women. The fraction is men/(men + women) or women/(men + women). In any case it's certainly a lot of commercials and FAR less then on HULU~!
You seem to be confusing a fraction to a ratio, which are two different things.
In the case of 1:4, or "one to four", that would imply five parts total. One part to four parts for a total of five parts. If expresed as a fraction it would be 1/5.
As opposed to 1/4, where it implies four parts total, or one part to the three others.
In your case of men to women being a 1:1 ratio, that would imply two equal parts. Would you state thisw fractionally as 1/1? As a fraction it would be 1/2 men and 1/2 women.