MS-RTA, Microsoft Real-Time Audio


Microsoft’s Real-time audio (MS-RTA) codec was introduced in 2006. MS-RTA is Microsoft’s proprietary audio codec and is subject to terms and conditions of Microsoft License agreement. It operates on 16-bit speech signals sampled at 8 KHz or 16 KHz and generates a compressed bit-stream having average bit-rates of 8.8 or 18 kbps respectively. It is a sub-band coder and has a look ahead delay of 10ms. The encoder optionally includes forward error correction (FEC) block to embed error recovery data in the bit-stream. The decoder has an optional jitter-control module that provides active management of jitter control and packet loss concealment. It is the default codec for Microsoft’s Unified Communications Platforms, and is designed for real-time, two way VoIP applications.

  • Based on Microsoft Standard specification
  • Optimized ASM/C implementation
  • Re-entrant implementation
  • C-callable APIs
  • Support for 8.8 kbps and 18 kbps average bit-rates.
  • Support for variable and fixed rate decoding.
  • Supports integrated Packet Loss Concealment (PLC) algorithm.
  • Support for direct-mode and pull-mode operation.
  • The implementation supports both Little-Endian and Big-Endian (on ARM and C64x+ platforms)
  • Optional support for xDM APIs.
  • Tested for bit-exactness with standard as well as a large database of non-standard test vectors
  • Module is fully interruptible (Maximum interrupt latency on C64x+ is 6000 cycles).
  • Tested for any illegal memory access by the module (C64x+ and ARM)
  • Tested for compliance with register preservation requirements
  • Tested for Input buffer corruption
  • Tested for I/O buffer alignment requirements
  • Tested for multi-instance implementation
  • Tested for 100% code coverage
  • Range validation for all the API parameters
  • Tested with scratch contamination at frame boundaries
  • Tested for packet loss conditions with 5% loss to 25% loss
  • Tested pull-mode decoder by simulating a large set of jitter conditions.
  • ARM implementation validated on OMAP3530 (Cortex-A8) and DM6446/DM6467 (ARM926EJ-S) platforms.
  • TI C64x+ implementation validated on Spectrum Digital C6455 DSK, DM6446 EVM and OMAP3530 platform.
  • TI C55x implementation validated on Spectrum Digital C5510 DSK

ARM9E, ARM11, Cortex-A8, Cortex-A9, TI C55x, and TI C64x+

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