Audio files download size hardly make sense

[im_a_lama (LAMA)]

Please select what you are reporting on:

Unreal Editor for Fortnite

What Type of Bug are you experiencing?

Audio

Summary

How are audio file sizes calculated??

I’ve just started trying to optimize a project that had apparently large audio files I’m not an audio pro but I can understand that lowering a quality related number should generally reduce the file size, I used audacity to perform some exports and test the file sizes, however : [image] (forgot to say that changing the bit depth doesn’t change anything either) Also, comparing to the original file sizes, the order is completely different [image] (this order makes much more sense actually) …

Steps to Reproduce

How are audio file sizes calculated??

I’ve just started trying to optimize a project that had apparently large audio files I’m not an audio pro but I can understand that lowering a quality related number should generally reduce the file size, I used audacity to perform some exports and test the file sizes, however : [image] (forgot to say that changing the bit depth doesn’t change anything either) Also, comparing to the original file sizes, the order is completely different [image] (this order makes much more sense actually) …

Expected Result

Audio files are too heavy and we don’t have any way to understand how the download size is computed and how to reduce it

Observed Result

Audio file download sizes doesn’t make sense (see thread)

Platform(s)

PC

Additional Notes

How are audio file sizes calculated??

I’ve just started trying to optimize a project that had apparently large audio files I’m not an audio pro but I can understand that lowering a quality related number should generally reduce the file size, I used audacity to perform some exports and test the file sizes, however : [image] (forgot to say that changing the bit depth doesn’t change anything either) Also, comparing to the original file sizes, the order is completely different [image] (this order makes much more sense actually) …

[im_a_lama (LAMA)]

bump

[audioSlacker (Michael)]

Hey there! Sorry for the confusion on this point.

When you import an audio file into UEFN (or Unreal Engine), it is automatically converted into a 16 bit Wav file. This is why you are seeing your a number of your different file formats returning similar sizes in the editor view.

Then, when the file is cooked, it is compressed using Bink compression, which is what is compressing your 22k 32 bit wav file from 43.4MB down to 6.4MB.

Currently the only way users have to lower the overall size of their audio is lowering the sample rate of the file before import.

This web page goes through how importing audio into UE is handled.

[im_a_lama (LAMA)]

Thanks for the answer, though I’m still not understanding things, I like the generic answer, however it doesn’t seem to explain the issues in my screenshot :

• Can I assume that the 48k and the 32k files have the same size because of the original file sample rate when I converted to 48k ? (which would mean that the 48k file is actually not sampled at 48k, but then why would the original file at the top be 1MB heavier ???)
• Why does the OGG quality seem to be randomly affecting the download size, a high quality ogg is lighter than a low quality ogg
• If files are converted to .wav, why does ogg seem to be heavier than wav files ?
• How am I able to get a single file down to 1.4MB (for which metadata seem to show a bit depth of 32b) on my end but the lowest I can go in UEFN is 5.1MB eventhough it’s supposed to be highly compressed through Bink ? (Also isn’t there some sort of unzipping happening to reduce download size which should make this even lower?)

Would be great if you could also tell us what are the plans for the future, are we going to have control over any of this ?

Thank you for your time

[LionUnchained (LionUEFN)]

Just to expand on this :
(and please let me know if this all checks out)

There is a key difference between audio file types is whether they are lossless or compressed.
WAV is a lossless file type, and what that means in application here is that the only control we have over the file size comes through the sample rate as the bit rate is constant.

For Lossless WAV files:

# Channels referring to mono or stereo (1 or 2)
Bit Rate = (Bit Depth) x (Sample Rate) x (Channels).

Since you know they’re going to convert this, then in this equation the only variable we have control over is the Sample Rate.

Standard sample rates are 48.0k and 44.1k in professional audio. The following example is a 44.1k .wav sample converted to a 22k .wav and a 22k .ogg file respectively.

The following image is the memory calculation in the map of the resulting files all uploaded. As you can see the memory gain is minimal and this has to do with the fact that Lossless files are not variable bit rate like lossy file formats such as .ogg or .mp3. You always have a minimum file size in this regard.

Since we must take into consideration that Epic has this audio import and compression process in place this instructs us on the optimal audio management approach. What may not be obvious but is very important is that you stand only to lose quality by ever converting your audio to a lossy format prior to this point in the process. What this means in practice is always try to get .wav files to begin, and try not to source audio files from .mp3s/.oggs/etc.

Based on Lama’s findings and some additional testing and my understanding of audio I came to the conclusion that the reason that he’s ending up with larger files has to do with the following (this is my best theory):

1. Digital Distortion: Digital audio is trying to recreate analog signals which are in the form of waves, when we compress and audio signal digitally we create artifacts and clipping, squaring off the digital signature of an originally rounder wave. (This creates digital distortion, think of a bit crusher effect). Because we’re doing this process back and forth we end up compressing (losing audio fidelity and dynamic range) and then expanding in a destructive way.

2. Artifacts = Data: Anywhere there is an audio signal written (not silence) would increase the file size (which is different than video compression where more black pixels = less total colors written = less memory usage, so degradation of the file would almost always reduce the file size).
   You’re essentially crunching down your wave forms (think of a bit crusher effect) and then expanding them and then crunching them down again.
   Because lossless has a minimum file size at a given sample rate you can theoretically both lose fidelity and gain file size in that way.

3. Encoding: Different lossy compression algorithms and settings (bit rates, sample rates, etc.) have varied efficiencies and ways of handling audio data. This variability can lead to situations where converting between formats and bit rates results in files that are larger than expected, without any improvement in quality and in fact, with a cumulative quality loss.

We can see this with Lama’s example and if you convert your own file from .wav to .ogg and then back to .wav you can experience this yourself.


What this leaves us with the option to reduce the sample rate which I would argue isn’t worth the cost when comparing the end result and measuring (Audio Quality : Memory Cost) as the value ratio:

retest8k is an 8k 16-bit .wav


There’s no other way to know the difference besides playing the audio file, and if you play these side by side you can be the judge of whether or not the quality loss is viable and set your sample rate to taste.

Personally I would look for memory savings elsewhere and stick to 44.1k 16-bit .wav files that have never been converted to a lossy quality.

[im_a_lama (LAMA)]

Bump

[Bug-Reporter]

FORT-894523 has been created and its status is ‘Unconfirmed’. This is now in a queue to be reproduced and confirmed.