No audio in downloaded files

[ghnp5]

Hello.
Thank you very much for releasing 5.1.0 !

I've just tried it on Highlights, and also Stories, and while the video downloads, the audio doesn't.

When using DevTools, I can see that the video and audio come in different files.
So, I'm not sure how this can be easily resolved by just using a piece of JavaScript in a bookmark. I'd say that we'd need the help of ffmpeg to merge the video and audio.

Maybe loading https://github.com/ffmpegwasm/ffmpeg.wasm could help automating all this, but the script will probably become a lot larger :)

[AaronLil]

There is already an open issue reporting this problem: #78. It seems that in some browsers, video delivery uses MPEG-DASH, or something like that.