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rdesktop/doc/rdpsnd.txt
Pierre Ossman 66f1511672 Even more information learned from Microsoft's client. 
git-svn-id: svn://svn.code.sf.net/p/rdesktop/code/trunk/rdesktop@1357 423420c4-83ab-492f-b58f-81f9feb106b5
2007-01-02 16:24:36 +00:00

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Overview
========
The RDPSND protocol is a binary, packet based protocol that maps
Microsoft's legacy wave API to a RDP channel.
All values are in little endian ordering.
Responses are sent with the same opcode as the request, and usually
also with the same packet structure.
The basic structure of a packet is:
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Opcode | Unknown | Payload size |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Opcode
Command or response type. Known values:
0x01 RDPSND_CLOSE
0x02 RDPSND_WRITE
0x03 RDPSND_SET_VOLUME
0x04 Unknown (4 bytes payload, no response)
0x05 RDPSND_COMPLETION
0x06 RDPSND_PING
0x07 RDPSND_NEGOTIATE
Unknown
Usage not known. Not valid when message comes from server
Payload size
Number of bytes following the header.
Opcodes
=======
Following is a list of all known opcodes and the contents in their
payloads.
RDPSND_CLOSE
------------
Tells the client that all applications on the server have released
control of the sound system, allowing the client to free any local
resources.
No payload and no response.
RDPSND_WRITE
------------
Request to play a chunk of data. The client is expected to queue up
the data and send a RDPSND_COMPLETION when playback has finished.
No response.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tick | Format index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Packet index | Pad |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Waveform data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Tick
Low 16 bits of clock tick count when packet was scheduled for
playback.
Format index
Waveform data format in the form of an index to the previously
negotiated format list.
Packet index
Index number of this packet.
Pad
Unused padding.
Waveform data
Binary waveform data in the format specified by the format index.
Size defined by the packet boundary.
Because of a strange design in Microsoft's server, the length of
the packet will be 4 bytes short and bytes 12 to 15 (4 bytes) of
the payload should be removed.
RDPSND_SET_VOLUME
-----------------
Request from the server to the client to change the output volume.
No response.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Left channel | Right channel |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Left channel
Volume of left channel in the range [0, 65535].
Right channel
Volume of right channel in the range [0, 65535].
RDPSND_COMPLETION
-----------------
Sent by the client to the server when a packet, queued by
RDPSND_WRITE, has finished playing.
No response is sent by the server.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tick | Packet index | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Tick
Clock tick count when packet finished playing on device.
Packet index
Index number of packet played.
Reserved
Reserved. Always 0.
RDPSND_PING
-----------
Sent by the server to the client to determine transport latency.
The client must respond by echoing the first four bytes of this
packet.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Tick | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Garbage |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Tick
Clock tick count when sent from server.
Reserved
Reserved. Always 0.
Garbage
1016 optional bytes of random data. Purpose unknown.
Only sent from server.
RDPSND_NEGOTIATE
----------------
Initial packet sent by server when the client [re]connects. Allows
the server to determine the capabilities of the client.
The client should reply with an identical packet, with the relevant
fields filled in, and a filtered list of formats (based on what the
client supports).
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Flags |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Left channel | Right channel |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Pitch |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP port | Format count |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Initial idx | Version | Padding |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Format tag | Channels |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Frames per sec. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Bytes per sec. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Block align | Bits per sample |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extra size | Extra data ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ... |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Flags
Flags for client capabilities. Data not valid when from server.
0000 0001 Do UDP song and dance (details unknown). Must be
set for sound to work.
0000 0002 Volume control support. Indicates that volume
fields are valid and that the client understands
RDPSND_SET_VOLUME.
0000 0004 Pitch field is valid.
Left channel
Initial volume for left channel. Data not valid when from server.
Right channel
Initial volume for right channel. Data not valid when from server.
Pitch
Initial pitch of the sound device. Data not valid when from server.
UDP port
Port used for UDP transfers. Sent in network (big endian) order.
Data not valid when from server.
Format count
Number of format structures following the header.
Initial index
Initial packet index. The first RDPSND_WRITE will have a packet
index one larger than this value. Data not valid when from client.
Version
Software version. Server (XP & 2K3) sets this to 5. Client (XP)
also sets this to 5.
Padding
Unused.
Format tag
Audio format type as registered at Microsoft.
Channels
Number of channels per frame.
Frames per sec.
Frames per second in Hz.
Bytes per sec.
Number of bytes per second. Should be the product of
"Frames per sec." and "Block align".
Block align
The size of each frame. Note that not all bytes may contain
useful data.
Bits per sample
Number of bits per sample. Commonly 8 or 16.
Extra size
Number of bytes of extra information following this format
description.
Extra data
Optional extra format data. Contents specific to each format
type.
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