Skip to main content

Notice

Please note that most of the software linked on this forum is likely to be safe to use. If you are unsure, feel free to ask in the relevant topics, or send a private message to an administrator or moderator. To help curb the problems of false positives, or in the event that you do find actual malware, you can contribute through the article linked here.
Topic: Converting AC3 / DTS to Opus. Am I overthinking this? (Read 1695 times) previous topic - next topic
0 Members and 1 Guest are viewing this topic.

Converting AC3 / DTS to Opus. Am I overthinking this?

I have some Dolby files which I'd like to listen to on my phone. Is there a way to figure out the optimal Opus bitrate, or am I displaying my ignorance?

A stereo AC3 file is about 10MB @ 256 kbps.  Converted to WAV it's ~60MB.

I naively thought that if I did
Code: [Select]
opusenc --bitrate 512 in.wav out.opus
it wouldn't use all 512, but reading the documentation, I understand it's a target. So the Opus file is twice the size of the original AC3.

Using
Code: [Select]
ffmpeg -i in.ac3 -b:a 256k out.opus
creates a file of the same size as the original AC3, obviously!

I assume that Opus is a lot more efficient that AC3 or DTS - so re-encoding to the same bitrate is a waste of time.  Is there a way to automatically figure out the best / most efficient bitrate?

Or, should I just accept that 128k ought to be enough for anyone and use that as default.

I'm prepared to be told that I'm being daft!  :)

 

Re: Converting AC3 / DTS to Opus. Am I overthinking this?

Reply #1
when decoding AC3 with ffmpeg i would use -drc_scale 0 to avoid dynamic range compression.
Code: [Select]
ffmpeg -drc_scale 0 -i in.ac3 -b:a 256k out.opus

Re: Converting AC3 / DTS to Opus. Am I overthinking this?

Reply #2
There is no easy answer because each compression algorithm uses a different psychoacoustic model and different parameters/compromises, and sometimes there are other changes & artifacts.   It could be worse with a higher opus bitrate. 

i.e. I'm pretty sure if you transcode from MP3 to MP3 multiple times at a higher bitrate each time the accumulated damage will eventually become audible. 

I'd just go with whatever you normally use and then if it "sounds bad" try a higher bitrate (or go lossless).

Re: Converting AC3 / DTS to Opus. Am I overthinking this?

Reply #3
The opus encoder's default bitrate (the one chosen if none is specified) is 96k. It gives very good quality audio, so if you're targeting efficiency that is a quality worth considering.
Youtube uses opus @160k for the default audio selection when available. If you're paranoid about audible encoding artifacts that's a safer selection. Any higher is probably excessive.

 
SimplePortal 1.0.0 RC1 © 2008-2021