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voip decoding

VoIP Decoding Software

VDSL is a software library used to decoded multimedia transmissions from recorded files and also in real-time from data streams.

VoIP Decoding Software

Audio and video is extracted from intercepted VoIP communications that are sent over mobile, LTE, and other IP networks – both from previously recorded files and real-time data streams. Decoded communications are output to standard file types which allows them to be examined and analyzed with greater ease. Audio and video decoding is available for a wide range of voice and video compression algorithms, and has useful applications for lawful interception and business.

The VDSL source code is optimized for DSPs, ARM and microprocessors from TI, ADI, Intel, and other leading vendors. Custom VoIP decoding and interception solutions can be arranged, and we invite you to make contact to discuss your requirements. Here’s a quick overview:

  • Automatic classification of voice, video, data, facsimile and non-standard or custom types
  • Extract and decompress the data of interest to standard file types
  • Information about extracted data is provided to the user
  • Support real-time processing on a continuous stream and pre-recorded data
  • Support secure protocols including SRTP and SSL / TLS
  • Support manual processing of partial or damaged recordings
  • Automatic and forced detection of non-standard signaling
  • Extract data in auto, manual and polling modes
  • Extract Caller ID, DTMF/MF tones and pulse dial information
  • Support libpcap network traffic captures
  • Support Windows and Linux operating systems, as well as embedded system platforms
  • Available as an executable or library (.dll/.so)
  • Available with our turn-key ATA hardware reference design

How it works

VDSL decodes audio and video from recorded files or real-time data streams of intercepted multimedia communications. It supports decoding of VoIP protocols including SIP, SDP, RTP/SRTP, RTCP and RTSP, and also supports SSL and TLS traffic.

VoIP sessions are established using SIP and SDP packets which identify the endpoints, method, media and other session parameters for communications.

During a VoIP multimedia session, audio and/or video is transmitted over an IP network as RTP packets. Data can be transferred using TCP, UDPTL over UDP, or RTP over UDP. By using the sequence numbers in each packet, along with any redundant or forward error correction (FEC) packets sent, the full media stream can be reconstructed and processed by the appropriate codec to reproduce the original content.

VoIP Lawful Interception Software

Input Data Format

File-based and packet-based inputs are accepted by the by the VDSL for both audio and video decoding purposes. A libpcap file (i.e. the output file from a packet sniffer like Wireshark) may be used as file input for the VDSL but it must contain the session control messages (SIP and SDP) sent by both participants during the session, and can contain any amount of RTP and non-RTP traffic. This information is necessary to reproduce the audio and video transferred during the call As much as possible of the session transmission should be included in the capture file, as the absence of certain messages might result in partial output or no usable output at all.

For the real-time processing of RTP streams, the data packets are input directly into the VDSL.

Output Data Format

The VDSL outputs audio in lossless .wav file format and/or an appropriate video file format. If required, additional file formats can be included or customized to suit your requirements. Generally, each input file will generate one output file and details of extracted audio and video is logged. Additional information is also captured by the VDSL to assist with analysis tasks and also for debugging purposes. Once complete, a concise report file is generated, giving the following relevant information for each output file: input file, source IP/port, destination IP/port, and for each file: length and compression.

Audio Codecs

  • ITU Speech Coders
    • G.711 – 64k bps PCM (A-law or μ-law form)
    • G.722 – 7 kHz audio coding within 64 kbit/s (SB-ADPCM)
    • G.722.1 – 24k and 32k bps, 7 kHz audio
    • G.722.2 – Adaptive Multi-Rate Wideband (GSM AMR-WB)
    • G.723.1 – 5 1/3k and 6.4k bps ACELP/MP-MLQ
    • G.726 – 16k, 24k, 32k and 40k bps ADPCM
    • G.727 – 5, 4, 3 and 2-bits sample Embedded ADPCM
    • G.728 – 16k bps LD-CELP
    • G.729/G.729A – 8k bps CS-ACELP
    • G.729 Annex B – Silence Detection
  • GSM Speech Coders
    • GSM-FR – GSM 06.10 Full Rate Vocoder
    • GSM-HR – GSM 06.20 Half Rate Vocoder
    • GSM-EFR – GSM 06.60 Enhanced Full Rate Vocoder
    • GSM-AMR – GSM 06.90 Adaptive Multi-Rate Vocoder
    • GSM-AMR-WB – 3GPP TS 26.171 Adaptive Multi-Rate Wideband (ITU G.722.2)
  • Wideband Speech Coders
    • G.722 – 7 kHz audio coding within 64 kbit/s (SB-ADPCM)
    • G.722.1 – 24k and 32k bps, 7 kHz audio
    • G.722.2 – 6.6k to 23.85k bps, 7 kHz audio (GSM AMR-WB)
    • Speex – 8 kHz, 16 kHz, and 32 kHz CELP
    • SILK – Variable Bitrate Wideband Speech Codec
  • Other Speech Coders
    • iLBC – Internet Low Bitrate Codec
    • LPC-10 – LPC-10
    • MELP – Mixed-Excitation Linear Predictive
    • MELPe – Mixed-Excitation Linear Predictive Enhanced
    • Opus – Interactive Audio Codec

Video Codecs

  • H.261
  • H.263
  • H.264


The following platforms are fully supported. This list is not exhaustive, so if your platform does not appear below then please contact us and we can let you know whether it is possible, and if customization needs to be done we’ll be able to give you an indication of cost and completion time (so that you can consider the feasibility of using that platform or this software).


  • Texas Instruments – C6000 (TMS320C62x, TMS320C64x, TMS320C645x, TMS320C66x, TMS320C67x), DaVinci, OMAP, C5000 (TMS320C54x, TMS320C55x)
  • Analog Devices – Blackfin, ADSP-21xx, TigerSHARC, SHARC
  • PowerPC
  • MIPS – MIPS32, MIPS64, MIPS4Kc
  • ARM – ARM7, ARM9, ARM9E, ARM10E, ARM11, StrongARM, ARM Cortex-A8, Cortex-M1
  • Intel / AMD – x86, x64 (both 32 and 64 bit modes)

Operating Systems

  • Google Android
  • Apple iOS / iPhone / iPad & MacOS
  • Unix,  Linux, μClinux, BSD
  • Microsoft Windows ACM / RTC / CE / Mobile
  • Symbian
  • eCOS / eCOSPro
  • Wind River VxWorks
  • Green Hills Integrity
  • Micrium μCOS