Not a historian, but an Italianist here, so I am going to try and answer your question the best I can using Italian as an example, where standardisation of accents is not tied to the media, but to literature and the unification of Italy.
Part 1: Blueprints:
What is today considered Italian is a descendant of the 13th century Florentine accent purified from some localisms and with some phonetical changes introduced (eg. diphthongs). This was done by none other than Dante Alighieri in his works. So, 13th century was the time when general ground rules for the standardisation were laid. This does not mean that anyone who isn't a native Italian speaker can flick trough the Inferno and make sense of it, the text is still plagued by some Latinisms, unfortunate abbreviations and most of all archaic words, but it is a blueprint of a language, nonetheless.
Part 2: Reformation (Kind of...)
Now, as mentioned before, Alighieri's language is very different from the modern Italian language, in fact what we refer to as Italian language wasn't even that common, the very accent that gave birth to it shifted significantly over the next couple of centuries and in different parts of Italy used different regional accents influenced sometimes by their neighbours or their rulers who weren't always Italian (eg. Aragons in the south). So, fast forward to the 19th century, cue Garibaldi and Risorgimento and BAM: you have a new country, a new nation, if you will is born in 1861 and the wider spreading of the standardised language ensues.
I should mention that they didn't just simply contrive some language invented in the 1200's, rather they used some of the works of the modern writers and poets. Most relevant (and this is just my opinion, so feel free to prove me wrong) is Alessandro Manzoni, who wrote the closest to the modern Italian and went trough the trouble of, in his own words, "Sciaquare i panni in Arno" (wash his clothes in the Arno - AKA went to Florence so that he could sample the language). This language started being used in the official documents, communications newspapers, and most importantly schools.
Part 3. Choice of the accent
With the invention of the radio and television, the accent which was similar to the one used academic and literary circles and upper classes was chosen. This accent wasn't spoken anywhere, per se, it was a form of "ideal Italian" (one could almost venture and say - an abstract). This accent is heavily used in modern TV programmes the whole nation understands it, but their everyday speech is sometimes drastically different (especially in the south of the country where even a proficient speaker can struggle to understand and take part in the conversation)
TL;DR Yes, other languages have chosen particular accents for their media but the route was not very simple or straightforward for Italian: Foundation laid in 1200's, revised in 1800's when it starts spreading trough the peninsula, is basically an "ideal language".
Gosh, even my TL;DR needs a TL;DR
Aaand Sources:
EDIT: Wording
Th term you're looking for is standard language. As said in the article, English is a pluricentric language, most other languages have only one standard form, usually derived from the accent of their capital.
Traditionally in the UK, Received Pronunciation has been the standard media accent (think BBC newscasters or Patrick Stewart), but in recent years Estuary has begun to creep up on it (think David Tennant on Doctor Who).
In German, I believe the accent from Hannover is the most prestigious, and in French it's the Loire valley. I was taught this while studying those languages, but never why.
"Standard Mandarin" is based largely upon the dialects spoken in the far far far northeast around the disgusting cesspit and hellhole of a city called Harbin. TV broadcasters speak this dialect, and most movies that aren't period pieces or for which accent is not crucial to the plot use it as well.
However, most American universities now teach Beijing dialect, which is very similar to Harbin dialect with a few quirks. Beijing dialect uses "er hua", a rhoticization at the end of words to make them diminutive, a good deal more than Harbin dialect, and has a some different rules regarding certain tonal shifts.