Gapk » History » Revision 13
Revision 12 (fixeria, 07/16/2018 04:29 PM) → Revision 13/18 (fixeria, 07/16/2018 04:30 PM)
h1. GAPK (GSM Audio Pocket Knife)
{{>toc}}
The GAPK (GSM Audio Pocket Knife) is a project, the product of which is a core library (libosmogapk) and a command-line tool (osmo-gapk) for conversions between the various GSM related codecs (HR/FR/EFR/AMR) and PCM audio. It supports many different formats for the codec frames, including ETSI and IETF standardized formats, as well as vendor-specific formats like those found in the TI Calypso DSP (see [[OsmocomBB:]]) and those of Racal 6103/6113 GSM test equipment.
h2. Supported Codecs
|_.Codec|_.Description|_.Implementation|
|pcm|Raw PCM signed 16bits samples|native|
|hr|GSM 06.20 Half Rate codec|libgsmhr[1] (GSM 06.06 reference code)|
|fr|GSM 06.10 Full Rate codec (classic gsm codec)|libgsm|
|efr|GSM 06.60 Enhanced Full Rate codec|opencore-amr|
|amr|GSM 26.061 Adaptive Multi Rate codec|opencore-amr|
[1] Note: due to the licensing problems, the GSM 06.06 reference *code is not included* as a part of GAPK. Moreover, the reference implementation has some additional problems, such as relatively low performance and poor code quality (lots of warnings, global state variables). Passing the _--enable-gsmhr_ configuration flag will enable the source code downloading, patching and compilation.
h2. Supported Formats
|_.Format|_.Description|
|amr-efr |Classic .amr file containing EFR (=AMR 12.2k) data|
|gsm |Classic .gsm file format (and RTP payload for FR according to RFC3551)|
|hr-ref-dec |3GPP HR Reference decoder code parameters file format|
|hr-ref-enc |3GPP HR Reference encoder code parameters file format|
|racal-hr |Racal HR TCH/H recording|
|racal-fr |Racal FR TCH/F recording|
|racal-efr |Racal EFR TCH/F recording|
|rawpcm-s16le |Raw PCM samples Signed 16 bits little endian|
|ti-hr |Texas Instrument HR TCH/H buffer format|
|ti-fr |Texas Instrument FR TCH/F buffer format|
|ti-efr |Texas Instrument EFR TCH/F buffer format|
|amr-opencore |Input format to libopencore-amrnb|
|rtp-amr |RTP payload for AMR according to RFC4867|
|rtp-efr |RTP payload for EFR according to RFC3551|
|rtp-hr-etsi |RTP payload for HR according to ETSI TS 101 318|
|rtp-hr-ietf |RTP payload for HR according to IETF RFC5993|
h2. Source Code
You can find the source code in git:
* http://git.osmocom.org/gapk/ (cgit web interface)
* @git clone git://git.osmocom.org/gapk@ for cloning the repository
h2. Common use cases
h3. Conversion between different codecs / formats
First of all, make sure that required codecs are supported by your build:
<pre>
$ osmo-gapk -h
...
Supported codecs:
name fmt enc dec description
pcm * Raw PCM signed 16 bits samples
hr * * * GSM 06.20 Half Rate codec
fr * * * GSM 06.10 Full Rate codec (classic gsm codec)
efr * * * GSM 06.60 Enhanced Full Rate codec
amr * * * GSM 26.071 Adaptive Multi Rate codec
...
</pre>
Example: *Example: converting .gsm (GSM FR codec) file to .amr (GSM EFR codec AMR 12.2k): 12.2k)*
<pre>
$ osmo-gapk -i input_file.gsm -f gsm -g amr-efr -o output_file.amr
</pre>
h3. RTP sink with audio playback on sound card
You can run @gapk@ as a _RTP sink_, i.e. listening to a given UDP port for incoming RTP frames, decoding them from their respective audio codec and then playing them back via your computers' sound card:
<pre>
$ osmo-gapk -I 0.0.0.0/30000 -f rtp-amr -A default -g rawpcm-s16le
</pre>
where
* *@-I 0.0.0.0/30000@* indicates the IP adddress (any) and UDP port (30000) to bind to and receive RTP frames on
* *@-f rtp-amr@* indicates the codec. Use *@gsm, rtp-efr, rtp-amr, rtp-hr-etsi or rtp-hr-ietf@* depending on your use case
* *@-A default@* is the alsa hardware device name (default is the default sound card)
h2. Contact / Mailing List
The project is too small to have it's own mailing list. Instead, we use the openbsc@lists.osmocom.org mailing list ("subscribe":http://lists.osmocom.org/mailman/listinfo/OpenBSC). Please observe the [[cellular-infrastructure:Mailing_List_Rules]].
h2. Authors
@gapk@ as written by Sylvain Munaut with contributions from Harald Welte.
It uses external libraries for the actual audio codecs, such as @libgsm@, @libopencore-amrnb@ nd the ETSI reference implementation for GSM-HR.
