[Freeswitch-users] .wav vs .gsm file sizes for recording calls.

Tue Jun 28 03:42:16 MSD 2011

On Mon, Jun 27, 2011 at 1:45 PM, Wes <wes-fs at 499x.com> wrote:

> **
> I'm sorry, but what is the SLIN format?  I tried that extension and it's
> invalid.  I searched the wiki and found nothing.
>
http://en.wikipedia.org/wiki/Linear_pulse-code_modulation

There's lots of names for it. Just think of SLIN as "the format normally
stored in a .wav file." (That's an imperfect definition but it will help you
get over the mental hump.)

In summary, just record to .wav files and x-code later when there are more
system resources available. You could also use "nice" or something like that
to prevent the x-coding process from grabbing all your system resources.

-MC

>
> On 6/27/2011 3:29 PM, David Ponzone wrote:
>
> You should really consider recording in SLIN, and then, batch compressing
> that later (during off-peak hours) to MP3 if you really need it to be
> smaller.
> Any efficient compression takes CPU, and you may want to avoid doing that
> live on your server.
>
>   David Ponzone  Direction Technique
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>
>  Le 27/06/2011 à 21:43, Wes a écrit :
>
>  I guess part of my confusion here was due to the term "raw data"
> mentioned in conjunction with the .gsm extension on the wiki page below...
> but actually gsm is a compressed format.
>
> http://wiki.freeswitch.org/wiki/Misc._Dialplan_Tools_record_session
>
> So, what is the best "compressed" format to use for recording voice (that
> is available as a direct recording format inside freeswitch)? There are tons
> of formats listed when I do "show file", but I tried a few and they are also
> giving me large files like the wav extension did. (au, for example)
>
> Even though the PCM/Wave format is preferred for voice quality, when we're
> talking about a 10:1 compression ratio, if the sound quality is still
> acceptable, I'd rather just record directly into the compressed format.
> We're talking about ~10- 20 minute recordings that will need to be
> transferred over the internet to a third party.
>
> On 6/24/2011 6:31 PM, Michael Collins wrote:
>
> I would caution you to consider adding disk space before you try to
> compress all your recordings. The 16 bit SLIN that FS normally puts in your
> wave files are pretty easy to handle, whether playing back in a FS session,
> or encoding for playback on some other device.
>
> An alternative might be to use lame to convert them to MP3's or ogg/vorbis
> files. If you look on the main FS conf call page you'll see I have the
> weekly recordings in multiple formats. (
> http://wiki.freeswitch.org/wiki/Weekly_Conference_Call#Past_Calls)
>
> Here are some stats for last Wednesday's call. Note that I record wave
> files in 48kHz then use sox to downsample to 16kHz wave, then I convert that
> 16kHz file into MP3 and Vorbis (in an ogg container). Here's what the
> results look like:
>
> <2831>:ls -1s conf_call_2011-06-15.*
>  18736 conf_call_2011-06-15.mp3
>  23044 conf_call_2011-06-15.ogg
> 199756 conf_call_2011-06-15.wav
>
> <2832>:file conf_call_2011-06-15.mp3
> conf_call_2011-06-15.mp3: MPEG ADTS, layer III, v2,  24 kBits, 16 kHz,
> Monaural
>
> <2833>:file conf_call_2011-06-15.ogg
> conf_call_2011-06-15.ogg: Ogg data, Vorbis audio, mono, 16000 Hz, ~48000
> bps, created by: Xiph.Org libVorbis I
>
> <2834>:file conf_call_2011-06-15.wav
> conf_call_2011-06-15.wav: RIFF (little-endian) data, WAVE audio, Microsoft
> PCM, 16 bit, mono 16000 Hz
>
> Note that the file sizes are in 1K blocks.
>
> So, bottom line is this: if you have the disk space then use wave. If you
> don't have disk space for wave then get some! :D If you REALLY need to use a
> different format then choose something like MP3 or Vorbis for long-term
> storage.
>
> -MC
>
> On Fri, Jun 24, 2011 at 2:26 PM, Wes <wes-fs at 499x.com> wrote:
>
>> In my tests, if I record a call in .wav format, a 10 second file is
>> about 177,000 bytes, while a 10 second .gsm file is 17,000 bytes.
>>
>> I  then used sox to convert the .gsm file to a .wav file, and it stayed
>> at around 17,000 bytes.  So, is the default recording format for .wav
>> using a higher sample rate? vs the default conversion format for the sox
>> tool?
>>
>> checking the file type using "file" I see that the larger one is:
>> RIFF (little-endian) data, WAVE audio, Microsoft PCM, 16 bit, mono 8000 Hz
>>
>> and the wav created by sox via the default conversion from .gsm is:
>> RIFF (little-endian) data, WAVE audio, GSM 6.10, mono 8000 Hz
>>
>> So apparently the larger wav file is 16 bit... how are these recording
>> parameters controlled?  Can I set it to record directly into the smaller
>> wav format? Or will I have to run sox on every file...
>>
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