♫ U+266B Beamed Eighth Notes use is defined as such in BBC Subtitle Guidelines:
"9.3.2 Characters permitted online
In addition to the characters above, the following characters are allowed if the subtitles are intended for online use only.
online € ♫ (replaces # to indicate music) ← → (arrows can replace < and >)."
♪ U+266A Eighth Note use is defined as such in Netflix Timed Text Style Guide:
https://partnerhelp.netflixstudios.com/hc/en-us/articles/217350977-English-USA-Timed-Text-Style-Guide
♫ U+266B Beamed Eighth Notes use is defined as such in BBC Subtitle Guidelines:
https://www.bbc.co.uk/accessibility/forproducts/guides/subtitles/#Characters-permitted-online
Both characters are widely used in subtitles.