AC-3 (Dolby digital plus) at 640 kb/s or AAC LC at 335 kb/s which is better

[Christopher2222]

I have heard that AAC is favored for it's higher sound quality at lower bit rates however AC-3 excels at delivering immersive sound experiences.

So just by the rates I've given in their formats, is it safe to say they are almost equal? Or could someone easily say hands down the higher bit rate AC-3 would/ should be the better audio?

Is there a clear winner here?

[pandy]

AAC is capable to deliver same or better quality at the same or lower bitrate but... AC-3 has probably highest market penetration from all multichannel capable codecs - so AAC is more modern and versatile but AC-3 is for sure most popular audio codec.

[syberdude]

I'm assuming you mean E-AC-3 (Enhanced Dolby Digital Plus) which is technically superior to AC-3 (Dolby Digital). Most Web platforms like Amazon or Netflix do 640kb/sec 5.1 or even E-AC-3 Atmos Joc 5.1 768kb/sec (sometimes you see 448kb/sec 5.1 or even in the 500 bitrate). The bitrate matters based on the amount of channel configuration and codec you use since they have different psychoacoustic models. For lossy uses I generally prefer QAAC (itunes based aac codec) as it can give you very good frequency range for smaller files at lower bitrate like 256kbps as its claimed to be transparent. Dolby usually requires either ffmpeg reverse-engineer codecs or licensed decoders to decode it but most encoders are usually ffmpeg. FFMPEG encoding of ac-3/eac-3 is reverse-engineered and is not perfect accuracy wise to licensed dolby encoders but close enough that its hard to tell the difference as its out of the hearing range. The issue comes down to Dialogue Normalization and DRC (dynamic range compression) when dealing with licensed decoders/encoders. If you want the most efficient codec around it would be Opus at 128kbps to 192kbps range. Youtube uses Opus as it works well within their bandwidth online infrastructure along with aac codecs. Downside to Opus audio codec is that it's only 48khz as far as I know and is not a perfect codec meaning it uses filters to approximate rather than to be exact like lossless can be or a superior codec like QAAC or even E-AC-3/AC-3 in many cases. I don't personally like ffmpeg's own AAC encoder as I feel it's lacking but it gets the job done technically. FDK-AAC is good but QAAC is considered best for a more natural sound and higher frequency range extension. You will want to do testing yourself to see which you find is best as that is usually the best way to know what suits you.

QAAC with setting q 127 will do better than either of those you asked about. I believe default for QAAC is q 96 setting which is generally transparent. Truth be told though lossless is best if you have the space but many may not so lossy does have certain options you can go with.

Hope some of this helps.