Re: [Tuxpaint-i18n] Reduced bitrate of many stamp description sounds

[Karl O. H. <ka...@hu...>]

[Sorry for the late reply to this.]

Bill Kendrick skreiv 12.01.2024 06:05:
> The other day I went through and converted all descriptive sound files
> in Tux Paint Stamps -- the sounds of people speaking the names of
> stamps -- from stereo to mono.  That saved almost 100MB of space
> used by those OGG files!

I think this is misguided. Ogg Vorbis uses channel coupling (similar to 
joint stereo in the MP3 format), and since the recordings have been done 
by (mono) microphones, converting from stereo to mono should in theory 
have *no* effect. I guess the reason that you saved 100 MB, is simply 
that you lossily recompressed a lossy format, further reducing the 
quality (introducing more artefacts).


> Today, I did further work, this time to reduce the bitrate of sounds,
> so they are never higher than 32,000bps.  That saved another 41MB.

Is this based on the already recompressed (mono) file? This will 
introduce even more artefacts. You will have have encoded the file 
*three* times, losing quality at each step:

     Original → Encode to Ogg → Reencode (mono) → Reencode (bitrate)

See https://wiki.hydrogenaud.io/index.php?title=Transcoding

It would be much better to encode to the final format from the 
*original* uncompressed files (if you have them).

I have tried listening to the transcoded Norwegian Nynorsk files. They 
were already in mono, so there is only a single recompression, but the 
audio quality is noticeably worse.

I have the original files, and can compress the files to ~ 32 kbps. This 
should results in much higher-quality files.

BTW, the algorithm for recompressing the files is also misguided. You 
first test if the bitrate is higher than 32 kbps. If it is, you 
recompress to 32 kbps. But the bitrate in Ogg Vorbis is a *nominal* 
bitrate, and you might actually end up with a file that is bigger than 
32 kbps after recompressing. Also, if the quality of the original file 
is such that it doesn’t *need* 32 kbps, you’re encoding at an 
unnecessarily *high* bitrate. It would better to specify the quality 
(e.g., the ‘--quality’ argument in oggenc, for example to -1).

BTW, would it be possible for Tux Paint to support the Opus codec? This 
results in much lower file sizes for the *same* quality. In my tests, I 
can get the same quality as my original Ogg files but halving the file 
size (by compress the original .wav files and using ‘opusenc --bitrate 
24’ – and note that despite the name, the ‘--bitrate’ argument specifies 
the *quality*, not the actual bitrate).


-- 
Karl Ove Hufthammer