[Freeswitch-dev] Questions on implementing mod_nelly codec

Anthony Minessale anthony.minessale at gmail.com
Wed Mar 23 00:19:17 MSK 2011

Are you planning to contribute this module?

On Mon, Mar 21, 2011 at 1:58 PM, Richard Alam <ritzalam at gmail.com> wrote:
> Hi,
> We've been trying to implement a mod_nelly codec but so far has been
> unsuccessful. We use a Nellymoser compatible codec submitted to ffmpeg
> (see June 16, 2008 entry of http://ffmpeg.org/).
> Our plan is to use Flash using Nellymoser to connect to a conference
> in FreeSWITCH.
> The hurdle seems to be that Nellymoser decodes 64 byte nelly audio to
> 512 byte L16. Nellymoser is 11-Khz 8-bit per sample with 32 ptime.
> However, L16 implementations are all 20 ptime
> which have uncompressed bytes in multiples of 320. This doesn't align
> with what mod_nelly expects when encoding (convert 512 bytes to 64
> bytes) and decoding (64 bytes to 512 bytes).
> Here is the SWITCH_MODULE_LOAD_FUNCTION(mod_nelly_load)
> [http://pastebin.freeswitch.org/15764] now. We've played around with
> the samples per second (SPS), actual samples per second (ASPS),
> bits per second (BPS), and the ptime (PTIME) but with no luck. It's
> either we get bad very choppy audio, incompatible destination (when
> codecs can't match), or no audio at all. We've managed to get the
> "You will now be placed into the conference" audio played correctly
> but the audio from the caller is bad. Just the paying of wav file from
> FS is correct.
> My question is how does transcoding works in FS? Am I correct to
> assume decoding as Nelly->L16 and encoding as L16->Nelly?
> So basically the media flow for our use case is Nelly -> L16 -->
> mod_conference -> L16 -> Nelly.
> Do I need to make the frames align? In this case, Nelly expect 256
> samples per frame while L16 has 160, 320, ... samples per frame.
> Hope I've articulated clearly what we are trying to accomplish.
> Suggestions and ideas on what to try out next is much appreciated.
> Thanks in advance.
> Richard
> --
> ---
> BigBlueButton
> http://www.bigbluebutton.org
> http://code.google.com/p/bigbluebutton
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Anthony Minessale II

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