Windows Media Audio Professional

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Windows Media Audio Professional (WMA Pro) is an improved lossy codec closely related to WMA standard. It retains most of the same general coding features, but also features improved entropy coding and quantization strategies as well as more efficient stereo coding. Notably, many of the WMA standard‘s low bitrate features have been removed, as the core codec is designed for efficient coding at most bitrates. Its main competitors include AAC, HE-AAC, Vorbis, Dolby Digital, and DTS. It supports 16-bit and 24-bit sample bit depth, sampling rates up to 96 kHz and up to eight discrete channels (7.1 channel surround).^[21] WMA Pro also supports dynamic range compression, which reduces the volume difference between the loudest and quietest sounds in the audio track. According to Microsoft‘s Amir Majidimehr, WMA Pro can technically go beyond 7.1 surround sound and support "an unlimited number of channels."^[22]

The codec‘s bit stream syntax was frozen at the first version, WMA 9 Pro.^[23] Later versions of WMA Pro introduced low-bit rate encoding, low-delay audio,^[24] frequency interpolation mode,^[25] and an expanded range of sampling rate and bit-depth encoding options. A WMA 10 Pro file compressed with frequency interpolation mode comprises a WMA 9 Pro track encoded at half the original sampling rate, which is then restored using a new compression algorithm.^[26] In this situation, WMA 9 Pro players which have not been updated to the WMA 10 Pro codec can only decode the lower quality WMA 9 Pro stream. Starting with WMA 10 Pro, eight channel encoding starts at 128 kbit/s, and tracks can be encoded at the native audio CD resolution (44.1 kHz, 16-bit), previously the domain of WMA Standard.

Despite a growing number of supported devices and its superiority over WMA, WMA Pro still has little hardware and software support. Some notable exceptions to this are the Microsoft Zune (limited to stereo),^[27]Xbox 360,^[28]Windows Mobile-powered devices with Windows Media Player 10 Mobile,^[29] newer Toshiba Gigabeat and Motorola devices,^[30][31] and devices running recent versions of the Rockbox alternative firmware.^[32] In addition, WMA Pro is a requirement for the WMV HD certification program.^[33] On the software side, Verizon utilizes WMA 10 Pro for its V CAST Music Service,^[34] and Windows Media Player 11 has promoted the codec as an alternative to WMA for copying audio CD tracks.^[35] WMA Pro is supported in Silverlight as of version 2 (though only in stereo mode). In the absence of the appropriate audio hardware, WMA Pro can automatically downmix multichannel audio to stereo or mono, and 24-bit resolution to 16-bit during playback.

A notable example of WMA Pro being used instead of WMA Standard is the NBC Olympics website which uses WMA 10 Pro in its low-bitrate mode at 48 kbit/s(a platform may support WMA 10 PRO with limitation of a max bitrate. namely, no more than the max bitrate such as 192kbps, able to decode while more than, unable to decode).

from: https://en.wikipedia.org/wiki/Windows_Media_Audio#Windows_Media_Audio_Professional

Windows Media Audio Professional

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原文地址：https://www.cnblogs.com/aspirs/p/9650328.html