Is it possible to make the code work more optimized?

Question

YouTube

Hello.
In general, I made such a code that converts a link to a youtube, vimeo and coub video into a player from these video hostings (if the latter can be called that).
I myself have been studying js for only 2 weeks, so I don’t know how to perform the following in a better way.

var $v1 = 'ССЫЛКА НА РОЛИК',
     $v2;

// Для youtube
if($v1.indexOf('youtube.com') + 1 || $v1.indexOf('youtu.be') + 1) {
  // Ищем и заменяем, чтобы проще обработать
  $v2 = $v1.replace('.com/embed/', '.com/watch?v=');
  $v1 = $v2.replace('.be/', '.com/watch?v=');
  //Отсеиваем ненужные части, чтобы получить чистый id
  $v2 = $v1.split(".com/watch?v=")[1];
  $v1 = $v2.split("&index")[0];
  $v2 = $v1.replace('&', '?');
  //Получаем чистый id, вставляем его непосредственно в плеер
  document.write('<iframe width="685" height="386" src="https://www.youtube.com/embed/' + $v2 + '" frameborder="0" allowfullscreen></iframe>');
} 
// Для Coub
else if ($v1.indexOf('http://coub.com/') + 1) {
  // Производим замену
  $v2 = $v1.replace('/view/', '/embed/');
  // Вставляем id в плеер
  document.write('<iframe src="' + $v2 + '?muted=false&amp;autostart=false&originalSize=false&hideTopBar=false&noSiteButtons=false&startWithHD=false" allowfullscreen="true" frameborder="0" width="685" height="386"></iframe>');
} 
// Для vimeo
else if ($v1.indexOf('vimeo.com') + 1) {
  // Производим замену
  $v2 = $v1.replace('vimeo.com/', 'player.vimeo.com/video/');
  // Вставляем id в плеер
  document.write('<iframe src="' + $v2 +'" width="685" height="386" frameborder="0" webkitallowfullscreen mozallowfullscreen allowfullscreen></iframe>');
} 
  //В случае, если не удалось обработать
else {document.write('<div style="color:red">Ошибка: не могу воспроизвести.</div>');}

As you can see, only 2 variables are used. Basically, the script searches and replaces, filters out unnecessary characters, and gets a clean id that it embeds into the player. So many actions have been done for youtube so that the script supports absolutely all types of links to videos: with timecode, from a playlist, etc.
The code itself does the job.
Make comments, point out my mistakes to me.
Tell me how to do the same, only better.

Answer 1

Don't skimp on variables, this is not assembler. In general, the dumbest thing is these pieces like

v1 = v2.something();
v2 = v1.somethingElse();

Debugging is a nightmare, modifying is like walking through a minefield.
document.write is not very good. blocks the page, and very destructively. In general, these places are not very neat, and I want to create a function that takes a URL, creates an iframe and inserts it in the right place.
Instead of a bunch of split and replace, you can use regular expressions, especially in the case of YouTube.
Do not use $ for variables, this is not PHP (in extreme cases, you can only if such a variable contains a jQuery object)