Apple doesn't support Opus via HLS yet, but if they ever do, they will
definitely expect "Opus" instead of "opus".
See https://mp4ra.org/#/codecsFixes: #10066
I moved the first application of the workaround out of the if block
so that it also applies to audio-only streams. The workaround was
extended likewise.
We should first and foremost adhere to the specifications and apply
workarounds afterwards for software that doesn't follow them. So I
turned around the workaround to first output the fLaC variant and then
the alternative flac variant.
Fixes: #10066
