Some streams really do use independent AC3 5.1 frames combined with an EAC3 dependent frame to add the extra channels for 7.1 (potentially replacing the existing surround channels)! It’s just not universal; most streams you’ll see use eac3 for both the dependent and independent subframes.
You’re spot on; we can’t use the upstream libavcodec decoder due to restrictions in our EAC3 license from Dolby. We could theoretically add support for dependent subframes in the parser, but it’d be somewhat complex to implement, so it hadn’t really been prioritized since as far as we’re aware the impact is purely cosmetic (displaying 5.1 on streams that actually play as 7.1 on supported devices). The original poster doesn’t seem to actually be affected by that issue, though (the meta we scan in is correct, probably because they’re on macOS, where we can rely on the OS-provided eac3 decoder).
@ymgenesis, if you’re running into quality issues and when direct playing, then I’m sorry to say that there’s not much we can do other than possibly disable DP of 7.1 eac3 on the affected device; we don’t really have much control of the playback stack on web-TV platforms. Could you check to see if the same thing happens when DSing instead of DPing?
