Bug Playing AAC 5.1 Audio In Videos

[CrashTestKing]

Plex is having issues with AAC 5.1 audio tracks in videos. I’m running the latest version of the server, although this has been a constant issue since I got my Roku Smart TV over a year ago. There’s actually two separate issues, but I suspect the root cause is tied together.

First, any time I watch something with a 5.1 AAC audio track, if I leave the Plex client with the default setting of “Auto” for Direct Play, then it always transcodes the audio. And, I might add, the transcoded audio is always quieter than the original. If I switch Direct Play to “Forced,” it plays the AAC track just fine without transcoding. As a workaround, I’m fine with leaving it on “Forced” for Direct Play since I know for a fact EVERYTHING in my library will play fine without transcoding. However, that causes the second issue…

If I have a movie with 2 or more audio tracks, where the first is 5.1 AAC and the second is anything else, it will ONLY play the second track, unless I switch Direct Play back to “Auto” and let it transcode the first track. The selection in the video’s setting’s indicate that the first track is selected, but that’s not what’s playing. I’m sure, because the only time I have 2 or more audio tracks is when I’ve got a movie in 2 languages OR I’ve got audio commentaries.

So for example, I tried to watch the 2005 film Constantine. First track is 5.1 AAC, second track is 2.0 AC3 and it’s a commentary track. If I leave it set it “Forced” for Direct Play, it shows that the 5.1 track is playing, but actually I’m getting the commentary track. If I switch it to “Auto” for Direct Play, it’ll play the 5.1 track but it also transcodes it and the volume comes through softer.

FYI, I couldn’t find a section specifically for bug reports (I’m still a bit new to these forums), so if there’s a better place to post this, let me know.

EDIT: This problem appears to be limited strictly to audio with more than 2 tracks. I just tested a TV show that has a single audio track that’s AAC 2.0, and it didn’t try to transcode it, even after switching Direct Play to “Auto”.

[boblinthewild]

Apparently a long-standing Roku limitation. See this for some more info:

Roku Plex ACC 5.1 to AC3 5.1 Transcode after latest update to V6.5.1

I assume the branded Roku is actually a variation of the 4640x, a 5th gen Roku Ultra. This model was the only one that has “advanced” Dolby Digital support. It can convert multi-channel AAC to AC3 internally, so while it’s direct playing, you are still receiving a converted AC3 stream. This internal process however does not produce good results (missing channels, muted volume, etc). Therefore we now use the PMS for converting multi-channel AAC to AC3. This has always been the case for every othe…

[CrashTestKing]

That kind of explains what I’m seeing. At least my first issue. But that’s the minor one.

The real issue is that if I set Direct Play to Forced, it plays the second audio track even though it indicates that it’s playing the first track. And nothing I do gets it to play the first track, unless I switch Direct Play back to Auto, and then I get transcoded audio that’s quieter than the original.

[boblinthewild]

Yes, that is definitely bonkers. Hopefully the Plex Roku experts will chime in.

[CrashTestKing]

Did a little bit further testing. My main concern was that if tried to avoid transcoding the audio, and the video had other audio tracks, it wouldn’t play the main (first) track.

So here’s the breakdown. The following behavior is what I get with Direct Play set to Forced. I used 2 versions of the same video file—They both had the same AAC 5.1 track, but one had an AC3 2.0 track and the other had an AAC 2.0 that I transcoded and remuxed with the original audio and video:

When the main track is AAC 5.1, and the additional track is AC3, then it will ONLY play the AC3 track. When the main track is AAC 5.1 and the other is AAC 2.0, then it will ONLY play the first 5.1 AAC track. The option is still there to pick any track, but whatever I pick, this is the behavior I get. So when there’s an AC3 track, it doesn’t matter which one I pick, only the AC3 track plays. When there’s only AAC tracks, it doesn’t matter which I pick, only the AAC 5.1 track plays. What’s frustrating is that if I look at the Plex dashboard, it shows the track that I’ve actually picked, even though that’s not the track that’s truly playing.

As soon as I switch Direct Play back to Auto, it goes back to playing exactly the tracks that I pick. However, if the track is AAC 5.1, it’ll transcode the audio (it won’t transcode at all if it’s AC3 or if it’s AAC 2.0). And the transcoded audio is always significantly quieter than the original.

Regardless of the way they intended to handle AAC 5.1 audio, this is definitely a bug.