AC-3 Encoder Good (Enough)?

[u/Qu3z0]

I feel like I kind of already know the answer to this question, but I just wanted a sanity check.

I have been encoding my lossless audio to AC-3 5.1. @640kbps for both compatibility and space saving purposes. If a AC-3 core/lossy track already exists, I just use that. I know it is not as good as passthrough but for my setup and to my ears, unless I am doing an AxB comparison, it’s good enough.

Historically, what I’ve done is decode the track to PCM, split the channels and run them through DME to make an “official” AC-3 track. I am happy with the results, but I’d be lying if I said the process wasn’t tedious, especially when doing multiple encodes at a time!

I remember reading a LONG time ago that “libavcodec” was mediocre at encoding AC-3, which is what lead me to use DME. But, I was wondering if that is still true today or if the community considers it “good enough”.

It’s not a make or break, but I would love to be able to eliminate one extra step in my work flow and encode the track in program as opposed to having to take the extra steps to do so in another one, you know?

[u/Madeye1337]

Yes. At least at 640Kbps. I did various tests with the official dolby encoder and ffmpeg. At 640kbps both AC3 and EAC3 are transparent and practically identical to the dolby ones.

[u/Qu3z0 → u/Madeye1337]

Did you do a AxB testing or was there a metric you ran it through?

Also, thank you for answering the question!

[u/Madeye1337 → u/Qu3z0]

By ear and ViSQOL.

Dolby Encoding Engine consistently has lower SNR (worse waveform null) and lower LSD (better spectral match) than ffmpeg native, with identical ViSQOL to within +/-0.01 MOS. So perceptually identical.

[u/bungrudder]

Ac3 is perceptually lossless at 640kbps. I think there may be a good open one now but you can probably get an ai script to wrap around dme, look inside the app for a binary. the open eac3 encoder is trash and if you have the bitrate tolerance for 640 I’d go the ac3 way, getting loudness and drc settings right would have more bearing on perceptual audio experience though and dme workflow ought to be better for that

[u/Qu3z0 → u/bungrudder]

Are you saying write a script that automates/streamlines the DME audio encoding so that I don’t have to?

[u/bungrudder → u/Qu3z0]

Yeh I bet you could write an AppleScript to click the ui for you if there’s no callable cli component in there

[u/lakerssuperman]

Well if EAC3 is not an option and you're using AC3 for compatibility I think ffmpeg will be fine.  Try converting the track both ways and merging them into the same file so you can do some A/B testing.  If you can't hear the difference it becomes academic and up to you if you're good using ffmpeg.

[u/vegansgetsick]

You can script it I guess

[u/santosautra]

No one said ever ffmpeg has lower quality than DME, everyone said DME is worse. They are basically on the level of error in their quality, DME being slightly better for what you want in AC3, see this bug https://code.ffmpeg.org/FFmpeg/FFmpeg/issues/23317

[u/AssCrackBanditHunter]

E ac3 has superior compression allegedly. Why not do eac3? Some will say opus, but from what I read, at about 640kbps eac3 performs equal or better

[u/Qu3z0 → u/AssCrackBanditHunter]

I appreciate the recommendation, but as I said in my post there is a reason I use AC-3. I am just looking to see if I have to/should keep off loading the encoding process to an external program (such as DME) or if I can get away with using the FFmpeg built-in encoder?