[Freeswitch-users] MP2

Steve Underwood steveu at coppice.org
Sun Jan 4 08:11:50 MSK 2015

On 01/04/2015 03:58 AM, Thomas Auge wrote:
> There seems to be: http://www.underbit.com/resources/mpeg/audio/compliance
That looks like a useful resource.
> Someone from the TwoLAME list recommended libMAD: http://www.underbit.com/products/mad/ ... it's GPL. Might be a good
> option.
The GPL licence rules out the use of MAD in FS.
> On 03.01.2015 14:57, Steve Underwood wrote:
>> Is there a standard set of test vectors for an MP2 decoder, and are they
>> expected to give bit exact results?
>> Steve
>> On 01/04/2015 01:27 AM, Thomas Auge wrote:
>>> A very interesting tech demo, but from his own readme, it might not be suitable for a freeswitch module:
>>>      - imprecise: due to the integer-only implementation, many rounding errors will
>>>        occur; expect a 45-55 dB noise margin!
>>>      - slow: it implements the synthesis process from the spec, which is very slow
>>>        (82 multiplications, 1-2 divisions and countless shifts and additions per
>>>        sample!)
>>>      - not robust: it may easily crash on broken input data. Also, it ignores CRC
>>>        values completely.
>>>      - not thread-safe
>>> A bit of a bummer, because a lightweight decoder on top of twolame would have been nice.
>>> On 03.01.2015 13:51, Steve Underwood wrote:
>>>> I have no idea how well it works, but there is this MP2 decoder -
>>>> http://keyj.emphy.de/kjmp2/
>>>> On 01/03/2015 07:00 AM, Brian West wrote:
>>>>> That looks like just the encoder, so we would need both the encoder
>>>>> and decoder that takes signed linear.  I'll be on the look out for an
>>>>> option too.
>>>>> On Fri, Jan 2, 2015 at 4:54 PM, Thomas Auge <auge at virtues.net
>>>>> <mailto:auge at virtues.net>> wrote:
>>>>>         > G722 can be a native bearer capability on an ISDN b-channel but thats not widely used.  MP2 in your case is just
>>>>>         > establishing a data channel be it via ISDN or IP.
>>>>>         Yup. I'm fairly certain that's what FreeTDM does for G722, else it
>>>>>         wouldn't make much sense to have a codec
>>>>>         configuration option. :)
>>>>>         > Before proceeding I would seek out a license compatible
>>>>>         encoder/decoder library that can be used, MP2 can mean so many
>>>>>         > things their are multiple levels, options and details required
>>>>>         to properly implement it.  I highly suspect its not an
>>>>>         > afternoon event, I could be wrong if the right library is found
>>>>>         thats license compatible.
>>>>>         There are a couple, T(w/o)oLame comes to mind.
>>>>>         (http://www.twolame.org/ LGPL licensed) Any pointers as to which
>>>>>         capabilities are needed in such a library? It seems the libraries
>>>>>         are as outdated as the codec. :)

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