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.

[Christopher2222]

Thanks. Some good info there. You're right I think I meant eAC-3, I'll have to dig up the file again. But it sounds like AC-3 or eAC-3 would be the winner here - I mean for a multi channel audio. I'm hard pressed to take a lower kb/s rate anyways.
Essentially I don't have a choice in setting the sound but rather choosing between two different videos. One has it set with AC-3 and the other with AAC.
I've also come to learn the AAC is the choice to use for general consumer audio and web streaming etc... whereas AC-3 is chosen for Home theatres DVD's Blurays .. higher end stuff basically.
The dilemma is the AAC is tagged to the video with the higher video bitrate where the AC-3 is tagged to the lower video bit rate video.

My idea was to see which audio was better and swap the best audio to the highest bitrate video using ffmpeg. If I found that both audio's were about the same then I would just leave the videos using, obviously the higher bitrate video.

Whoops, I failed to mention both audio files are 6 channel. I'm leaning towards moving the AC-3 audio over, ... at least i think I'd feel a better audio sound with the AC-3 being at a higher kb/s, does that sound correct?

[syberdude]

QAAC can go from stereo up to 7.1 channels. I generally just use the terms DD or DDP to keep track if i name my files but mediainfo uses AC-3/E-AC-3 etc terms for technical reasons. The general issue with AC-3 or E-AC-3 is normally limited frequency range which is often 20khz peak ceiling unless you use custom filters to allow it to go higher but if your bitrate is low enough then it won't go higher than 18khz. For audiophile/fidelity types they normally want the best true frequency response you can get from files instead of the idea of fake or lower quality audio files. For BluRay/Receivers/media boxes using AC-3/E-AC-3 can just make things easier. I'll put a link to Spek-X for you so you can take a look and get an idea of things. You can use Spek-X to take images of frequencies for sound and then use AI sites like duck.ai or search.brave.com/ask or even google.com/ai to help you figure out what is best or not when you upload images for it to see. I understand what you are asking and truth be told you can probably have all this figured out in minutes using AI chat systems to give you good information.


https://github.com/MikeWang000000/spek-X
https://github.com/MikeWang000000/spek-X/releases/download/v0.9.4/spek-x-0.9.4-windows-x86_64.zip

Understanding how frequencies work and what you prefer will help you get the results you want. I'd look into MKVToolnix to use it so you can Muxing/Demuxing file containers. I'd also get clever FFmpeg-GUI to make things easier for you just in case. I, myself, use the programs EZ CD audio converter or Xrecode3 here and there for specific audio encodes. Sometimes though you can use bat files along with ffmpeg to do many things other than command line. I'd recommend eac3to with UsEac3to142 (gui for eac3to) for encoding, especially if you want to use ffmpeg. Most of these programs are on videohelp or listed for you to find them.

AC-3 in DVD days was often done at 192kb/sec for stereo. Nowadays, WEB-DL releases are done with 224kb/sec in E-AC-3 for stereo. When you go multi-channel you need higher bitrate for more channels. Typical WEB-DL does 640kb/sec for 5.1 (6 channels) and then when doing atmos which is object based sound (don't get confused by just bed channels like 5.1 which is fallback) you will often see 768kb/sec or lower 448kb/sec (possibly 500 range) if they are trying to save on space/bandwidth to be more efficient. Higher bitrate is normally better as you'd think but it can be overkill and it depends upon you and your needs.