CD and DVD Media Playback

WDM audio supports the following features for CD and DVD media playback under the Windows 98 and Windows NT 5.0 operating systems:

A kernel-mode CD-ROM driver that emulates MSCDEX commands and implements reading, parsing, and streaming of Red Book CD digital audio to the kernel-mode WDM system-wide mixer at 16-bit 44.1 kHz.
A Universal Disk Format (UDF) DVD file reader, splitter, and navigator that provides access for DirectShow clients to separate video and audio streams.
A kernel-mode, system-wide software mixer, which supports DirectSound, DirectShow, and MMSYS clients, plus kernel-mode WDM filters, including Red Book CD-ROM and MIDI drivers. The architecture provides the ability for algorithms from any vendor to decode the DVD audio, and it supports mixing at 16-bit 48 kHz.
Flexible control of the output destination. The WDM drivers can send the master 16-bit 44.1-kHz or 48-kHz or other format output to an ISA, PCI, USB, or IEEE 1394 audio device. Additionally, support is provided for redirection of the PCI-device final-mix output to USB speakers.

Baseline PC 98 audio hardware support for CD-ROM and DVD media playback requires that the built-in or external audio codec support playback of 16-bit stereo PCM data at either a 44.1-kHz or 48-kHz sample rate. For a list of the PC 98 requirements, see the “Basic Audio Requirements” section later in this chapter.

For MPEG content, the system designer might choose to include optional DirectShow or WDM kernel-mode streaming filter components or hardware that can provide the following capabilities:

Greater than 85-dB dynamic range codec audio quality to the performance requirements of the consumer-electronics market
Software or hardware Dolby AC-3 or MPEG-2 multichannel decode and downmix to stereo at 16-bit 48 kHz
Software or hardware MPEG-1 layer-2 stereo at 16-bit 32, 44.1, or 48 kHz
Software or hardware support for up to 24-bit 96-kHz linear PCM (LPCM) data, down-converted to 16-bit 48 kHz.

The following table presents actual measurements collected by IAL for software Dolby AC-3 decode on Intel Pentium II processors with MMX technology.

Performance Measurements for Dolby AC-3 Decode

Function 233-MHz Pentium II processor¹

Dolby-certified 5.1-channel AC-3 decode and downmix to ProLogic-encoded stereo at 48 kHz 8%

Optional Dolby-certified virtual surround for rear channels, two channels at 48 kHz 12%²

Total for AC-3 decode with HRTF 3-D virtual surround 20%

¹Actual performance is dependent on specific processor, chip-set, memory, and I/O subsystem implementations, as well as the software implementation (integer, FP, or MMX technology). To estimate the performance on other processor speeds with Intel MMX technology, use a ratio based on the processor’s MHz rating.
²HRTF 3-D virtual surround performance is based on 3Q1997 release of Intel 3D RSX; performance of the 1Q1997 3D RSX is 24 percent.

Full-Duplex H.323/H.324 Video and Audio Conferencing

WDM audio supports the following features for full-duplex video and audio conferencing under Windows 98 and Windows NT 5.0:

Native 32-bit DirectSound support for simultaneous audio input and output, not dependent on 16-bit MMSYS components
Input and output position reporting mechanisms for synchronization of speaker and microphone streams, accurate to 1 ms or better
WDM Stream class driver that provides access to acoustic echo cancellation (AEC) reference interfaces supported by hardware codecs
WDM system audio filter graph that supports insertion of a non-Microsoft kernel-mode AEC filter module adjacent to the WDM Stream class driver in both the input and output streams

Baseline PC 98 audio hardware support for H.323/H.324 video and audio conferencing requires full-duplex audio capability. For a list of the PC 98 requirements, see the “Basic Audio Requirements” section later in this chapter.

The system designer might choose to include optional hardware to provide the following capabilities:

Full-duplex operation at independent sample rates for simultaneous 8-kHz microphone input and 44.1-kHz speaker output
Hardware AEC references for echo cancellation filtering

The following table presents actual measurements collected by IAL for H.323/H.324 audio on Intel Pentium II processors with MMX technology.

Performance Measurements for H.323/H.324 Audio

Function	233-MHz Pentium II processor¹
Full-duplex G.723.1 encode and decode, mono at 8 kHz	10%
Full-duplex AEC, mono at 8 kHz	6%
Total H.323/H.324 audio	16%
¹Actual performance is dependent on specific processor, chip-set, memory, and I/O subsystem implementations, as well as the software implementation (integer, FP, or MMX technology). To estimate the performance on other processor speeds with Intel MMX technology, use a ratio based on the processor’s MHz rating.

Function	233-MHz Pentium II processor¹

Dolby-certified 5.1-channel AC-3 decode and downmix to ProLogic-encoded stereo at 48 kHz	8%
Optional Dolby-certified virtual surround for rear channels, two channels at 48 kHz	12%²

Total for AC-3 decode with HRTF 3-D virtual surround	20%

¹Actual performance is dependent on specific processor, chip-set, memory, and I/O subsystem implementations, as well as the software implementation (integer, FP, or MMX technology). To estimate the performance on other processor speeds with Intel MMX technology, use a ratio based on the processor’s MHz rating. ²HRTF 3-D virtual surround performance is based on 3Q1997 release of Intel 3D RSX; performance of the 1Q1997 3D RSX is 24 percent.