@burnout426 I can say it's getting worst. At first it was maybe 2-3 videos a day that had this problem but now most of the videos I saw on twitter has this.
If you wanna compare two here is a link.
Length : 56 seconds,audio is gone after 9 seconds
Length : 44 seconds, audio is perfectly fine
Edit: Also the fullscreen solution works.When the video is fullscreen, audio spikes up at 9 second so it is either a problem about how opera handles .ts file extension or how Twitter streams these.If you go fullscreen before 9 seconds you can turn it back to normal and it works fine.