Subtitles in movies

During any movie with subtitles I can observe written actions like "music playing" "engine turns over". What exactly happened to articles? Conjugation verbs? Thanks


Solution 1:

Brevity...

They are of minor importance, simply scene-setting or context and are not intended to be spoken.

If they were spelled out, with full grammatical accuracy [I think] they could distract from the main task - following the plot.