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Converting from mp3 to aac - should I use the same sample/birate?

I'm currently in the process of converting a few thousand videos and some of them use mp3 audio and we have to switch them over to AAC.

My question is: Should I retain the same bitrate of the audio tracks or Should it be higher or lower?

For instance, one video uses an mp3 audio track running at 44.1kHz/128kbit - I then convert it to AAC at the same 44.1/128 - I obviously have the option to change those and either increase or decrease them.

I'm familiar with the concepts at hand here such as the audio quality will absolutely NOT improve but I'm speaking about the desire to RETAIN as much of the original audio as possible. Would it be beneficial to change either of those or should they just be left the same as the sources'??

Re: Converting from mp3 to aac - should I use the same sample/birate?

Reply #1
You will technically lose quality no matter what bitrate or other parameters you use for such a conversion.

FYI:
http://wiki.hydrogenaud.io/index.php?title=Transcoding#Lossy-to-lossy_transcoding

Why you want to do that? The video container format doesn't support mp3? Player compatibility? Are there any alternatives to avoid transcoding?

Re: Converting from mp3 to aac - should I use the same sample/birate?

Reply #2
Well, AAC itself is more efficient for the same bitrate than MP3 (I'm talking about best codecs of each format), and transcoding artifacts are worse when transcoding to the same codec than to a different codec (at least on some tests that were carried here at hydrogenaudio) so while you don't have the best scenario, it might be acceptable.

So yes, I suggest to keep the same bitrate. Increasing it might give an incorrect sign of higher quality and decreasing it could boost the artifacts from transcoding.

Re: Converting from mp3 to aac - should I use the same sample/birate?

Reply #3
... AAC itself is more efficient for the same bitrate than MP3 ...
So yes, I suggest to keep the same bitrate. Increasing it might give an incorrect sign of higher quality and decreasing it could boost the artifacts from transcoding.

Ahh I hadn't considered such transcoding artifacts and I completely agree with you on the matter of the perception issue it could cause if it were increased...

FYI:
http://wiki.hydrogenaud.io/index.php?title=Transcoding#Lossy-to-lossy_transcoding

Why you want to do that? The video container format doesn't support mp3? Player compatibility? Are there any alternatives to avoid transcoding?


Thanks for the link to the lossy-to-lossy transcoding wiki section!

I have to do this so it works with some streaming software. Apparently it doesn't like WAV, PCM, OGG, MP3 but will take any AAC we throw at it.

The plan is to stream these videos all live in playlist and while I do know of ways to get it working, the organization's software doesn't appear to accept anything other than AAC well. Its not really my choice either so I just wanted to know if there was anything I could do to "retain" as much of the original audio signal as possible.


Thank you both very much! This has been illuminating!

 
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