opus - May 2017 - how to compress 93gb speech mp3 files to opus files

Hi I am Rupesh from India. I have a huge directory of size 93.5 gb with
8500 mp3 files and 2000 sub directories.

All these mp3s are speeches recorded by someone at 64 kbps. I want to
compress these files recursively to opus using lame or another tool with 16
kbps bit rate and 11050 sample rate.

I have compressed the above huge directory with above options using ffmpeg
and the resulted destination directory size was 29.5 gb and the quality was
not good. Then I thought instead of compressing to mp3 it is better to
compress and convert to opus.

I have compressed some mp3 files to opus recursively with foobar2000 and
lamexp(a gui front end for lame) and the resulted opus files were
satisfactory.

The quality of opus file generated is much higher than mp3 file generated
using same bitrate and same sample rate. The quality I mean there are less
sounds like shhh garrrr and other electronic sounds.

So I have decided to compress and convert all these mp3 speech files to
opus.

I have examined some tools like ffmpeg,lame,foobar. lamexp tool is taking
much time to convert and foobar is taking very much less time to convert. I
want to maintain high quality in resulted opus files I mean I want a tool
which can take maximum time and produce good opus file.

Can anyone of you suggest which is the best tool to convert and compress
mp3 files recursively to opus. Please try to suggest 3 options I mean at
8kbps,16 kbps, 24 kbps with the corresponding sample rates which are
perfectly suitable. Also suggest how to reduce noises if any in resulted
opus files.

I think that there is no player for opus files in android and if you know
any please suggest the best one possibly which can play files in folder
view.


Regards,
Rupesh.
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I have converted 93 GB of mp3 speech files to opus using dbpoweramp with
settings 16 kbps bitrate,48000 sample rate,channels count set to 1 ie.,
mono.

80 percent of the files are same in quality with source files and 20
percent are poor in quality compared with source files. Poor quality I mean
I can't get exact voice while listening  to opus files. Some of the files
are in low volume and some files are having rise and fall in volume.

Please suggest how to maintain same volume through out all the file. I
think that to maintain same volume there are some DSPs like volume
normalization, replay gain etc., in foobar, dbpoweramp. Are there any
filters or DSPs to remove noise in foobar, dbpoweramp while converting mp3
to speech files.
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