Windows Media Audio Professional
Profiles
WMA Pro currently supports four profiles for consumer electronics devices. The specifics
for each profile are outlined in the following table. A device that is capable of
supporting a stream with a given profile is also capable of supporting a stream
with a lower profile. For example, if a device can support an M3 profile stream,
it can also support M0, M1, and M2 profile streams.
Windows Media Audio Professional Profiles
|
Profile |
Property |
Value |
Comments |
|
M0 |
Max bit rate |
192,000 bits per second (bps) |
Recommended for low-bandwidth scenarios like over-the-air (OTA) download of music
& streaming. Observe that the maximum rate in an audio frame is 1,536,000 bits/sec.
|
|
Max sampling rate |
48,000 Hertz (Hz) |
|
Max number channels |
2 |
|
Max buffer size |
600*1,024 bits |
|
Max samples per audio frame |
2,048 |
|
Max bits per audio frame |
65,536 |
|
M1 |
Max bit rate |
385,000 bps |
Recommended for surround sound for standard-definition movies. Observe that the
maximum rate in an audio frame is 1,536,000 bits/sec.
|
|
Max sampling rate |
48,000 Hz |
|
Max number channels |
5.1 (6) |
|
Max buffer size |
600*1,024 bits |
|
Max samples per audio frame |
4,096 |
|
Max bits per audio frame |
131,072 |
|
M2 |
Max bit rate |
769,000 bps |
Recommended for surround sound for high-definition movies. Observe that the maximum
rate in an audio frame is 3,072,000 bits/sec.
|
|
Max sampling rate |
96,000 Hz |
|
Max number channels |
5.1 (6) |
|
Max buffer size |
1200*1,024 bits |
|
Max samples per audio frame |
4,096 |
|
Max bits per audio frame |
131,072 |
|
M3 |
Max bit rate |
3,000,000 bps |
Recommended for surround sound for high-definition movies and digital theater. Observe
that the maximum rate in an audio frame is 3,072,000 bits/sec.
|
|
Max sampling rate |
96,000 Hz |
|
Max number channels |
7.1 (8) |
|
Max buffer size |
2,400*1,024 bits |
|
Max samples per audio frame |
4,096 |
|
Max bits per audio frame |
131,072 |
The following list defines the terms used in the above table.
- Max bit rate
-
The maximum average bit rate allowed for the audio stream allowed under a given
profile. Note that all profiles have a Max bit rate that can be supported
with IEC61937 encoding.
- Max sample rate
-
The maximum audio sample rate per channel.
- Max number channels
-
The maximum numbers of channels that are supported for a given profile.
- Max buffer size
-
This property relates to decoding requirements for the compressed bitstream buffer.
- Max samples per audio frame
-
The number of samples in an audio frame, per the IEC61937 definition of audio frames.
- Max bits per audio frame
-
The maximum number of bits that can be used for coding an audio frame.
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Sink Indication of WMA Pro
Support
The ability for a CEA-861-D-compatible sink to receive and decode a WMA Pro audio
stream is indicated via a CEA Short Audio Descriptor in the Audio Data Block within
the CEA Timing Extension (Version 3) of the sink's extended display identification
data (EDID). The format of the Short Audio Descriptor for WMA Pro is shown in the
following table.
WMA Pro Short Audio Descriptor Format
The Audio Format Code is 14 (0xE, 4'b1110) for WMA Pro in CEA-861-D. The maximum
number of channels supported depends on the profile for the WMA Pro support. (See
the first table, Windows Media Audio Professional Profiles.) The audio sample rates
that are supported are also dependent on the supported profile. At this time, 192 kilohertz
(kHz) and 176.4kHz audio samples rates are not supported by the any of the defined
profiles, so these indicators should be set to 0 in the Short Audio Descriptor.
For byte 3 of the Short Audio Descriptor, the 3 lsb's are used to indicate
the profile. A value of 0 maps to profile M0, a value of 1 maps to M1, and so on.
See the following table for a list of the profile code mapping.
Profile Code Mapping
|
Profile code |
Profile |
|
0 |
M0 |
|
1 |
M1 |
|
2 |
M2 |
|
3 |
M3 |
|
4-7 |
Reserved |
The upper 5 bits of byte 3 are currently reserved.
The encoding mechanism for WMA Pro over CEA-861-D is similar to sending WMA Pro
over IEC61937. Refer to the draft of IEC61937-8 "Digital audio—Interface
for non-linear PCM encoded audio bitstreams applying IEC 60958—Part 8: Non-linear
PCM bitstreams according to the Windows Media Audio Professional (IEC 100/709/NP:2003)"
which can be ordered from the IHS, Inc. Web site at http://www.ihs.com/.
In section 4.2 of the IEC61937-8 draft, the "type" of the supported
stream is referenced. This is not necessarily equivalent to a profile indication.
The following table shows the "type" mapping for each profile.
IEC61937-8 Profile/Type Mapping
|
Profile |
Type |
|
M0 |
II |
|
M1 |
I |
|
M2 |
I |
|
M3 |
I |
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Source Indication of WMA
Pro Stream Content
CEA-861-D defines an Audio Info Frame Data Packet. The information in this packet
may be useful in identifying the audio. The Audio Coding Type (CT3-CT0) field in
the packet can be set to 14 (0xE or 4'b1110) to indicate WMA Pro. It should be noted
that HDMI requires that CT3-CT0 is set to 0 to avoid conflicts with the same information
in the IEC 61937 BurstInfo. For additional details, see the HDMI 1.2 specification,
which is available from the HDMI Web site at
http://www.hdmi.org/.
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For More Information
For more information about WMA Pro and how to compress pulse code modulation (PCM)
audio data using WMA Pro (specifically, how to do so for the relevant profiles),
see the following Microsoft Web pages:
For more information about how to packetize a WMA Pro stream for IEC61937 transmission,
refer to the IEC61937-8 draft, which can be ordered from the IHS, Inc. Web site
at http://www.ihs.com/.
For more information about how to packetize an IEC61937 compliant stream for HDMI
transmission, refer to the HDMI specification, which is available from the HDMI
Web site at http://www.hdmi.org/.
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