On Tue, Sep 18, 2012 at 7:21 PM, George Niculae <[email protected]> wrote:
> On Wed, Sep 19, 2012 at 1:35 AM, Jeff Pyle <[email protected]> > wrote: > > Hi George, > > > > Thanks for the quick reply! > > > > The record rate (sample rate) is no issue. Through the web GUI I can > choose > > either 8khz or 16khz, as you indicate. I'm referring to attributes > unique > > to MP3 creation, specifically, the bitrate. This is related to the audio > > compression in the MP3 encoding process. > > > > I don't have a file up in front of me but I seem to remember it > compresses > > at 16 kbps (not to be confused with the 16 kHz sample rate). I'd like > to at > > least double that to 32 kbps, or as I mentioned, variable bitrate at a > > selectable quality setting would be phenomenal. > > > > Does that make sense? I'm trying to wring out some of the warble > inherent > > to a 16 kbps MP3. Efficient with filesize, but you pay for it in audio > > quality. > > > > Yep, it does. There are options to add in > /etc/sipxpbx/freeswitch/conf/autoload_configs/shout.conf.xml as > > <param name="encode-brate" value="32"/> > <param name="encode-resample" value="44100"/> > <param name="encode-quality" value="0"/> > > (support added with http://jira.freeswitch.org/browse/FS-1231) > > didn't play with them, please report back with findings This is exactly what I was looking for. mod_shout seems to use the Lame library so these options translate to lame command line options, if one were familiar with those. The "encode-brate" sets the encoder to use a fixed bitrate, specified in kbps. Equivalent to the "-b" option on the lame command line. 8 kHz sources can use any value 8-64 kbps at multiples of 8, while 16 kHz sources can use 8-160 kbps on the multiples. I find 64 kbps to be an acceptable improvement over the default for 16 kHz recordings. Similarly, 32 kbps for 8 kHz is just fine. The "encode-resample" value forces the encoder to resample at the specified rate. Equivalent to the "--resample" option on the command line. If you don't set this, the sample rate of the resulting MP3 will be whatever is set in the sipX web GUI / sipxivr.xml. Leaving it default makes sense to me. The "encode-quality" value sets the noise shaping and psycho-acoustic algorithms of the encoder. mod_shout's default is 2, equivalent to a "-h" high-quality setting on the command line. I don't see any reason to ever change this. Setting it to 1 might squeak out a touch more fidelity, but lame warns that it's "...slow and may not produce significantly higher quality [than the default]." Point taken. Unfortunately mod_shout doesn't appear support lame's variable bitrate options. Bummer, that would have been fun. The bottom line? I set the "Record rate" on the System -> Voicemail page to 16000, and I added one line to /etc/sipxpbx/freeswitch/conf/autoload_configs/shout.conf.xml: <param name="encode-brate" value="64"/> Life is good. A 64 kbps MP3 @ 16 kHz and a 32 kbps MP3 @ 8 kHz are a quarter the size of their WAV equivalents with a quality high enough most folks can't hear any compression artifacts at all. Works for me. - Jeff
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