在运行 VirtualBox 1.6.28 的 Gentoo Linux 主机上，我无法协商 VRDP（RDP-4 版本）连接，因为 rdesktop-vrdp 客户端无法初始化声音，因此根本无法连接，即使虚拟机未启用声音和一个参数被传递给rdesktop客户端来禁用它！
hatsumemio@mintpc:~$ rdesktop-vrdp -4 -a 16 -N localhost:3394 -r sound:off
Autoselected keyboard map en-gb
ERROR: channel_register
WARNING: Initializing sound-support failed!
ERROR: Connection closed
我的 VRDE 设置
VRDE:
enabled (Address 127.0.0.1, Ports 3394, MultiConn: off, ReuseSingleConn: off, Authentication type: null)
VRDE port: 3394
Video redirection: enabled (Quality 80)
VRDE property : TCP/Ports = "3394"
VRDE property : TCP/Address = "127.0.0.1"
VRDE property : VideoChannel/Enabled = "1"
VRDE property : VideoChannel/Quality = "80"
VRDE property : VideoChannel/DownscaleProtection = <not set>
VRDE property : Client/DisableDisplay = "0"
VRDE property : Client/DisableInput = <not set>
VRDE property : Client/DisableAudio = "1"
VRDE property : Client/DisableUSB = "0"
VRDE property : Client/DisableClipboard = "0"
VRDE property : Client/DisableUpstreamAudio = <not set>
VRDE property : Client/DisableRDPDR = <not set>
VRDE property : H3DRedirect/Enabled = <not set>
VRDE property : Security/Method = <not set>
VRDE property : Security/ServerCertificate = <not set>
VRDE property : Security/ServerPrivateKey = <not set>
VRDE property : Security/CACertificate = <not set>
VRDE property : Audio/RateCorrectionMode = "VRDP_AUDIO_MODE_LPF"
VRDE property : Audio/LogPath = <not set>
声音设置
Audio: disabled
Audio playback: disabled
Audio capture: disabled
VirtualBox 官方手册的“远程桌面”一章没有提到如何使声音工作。因此，我的问题是：如何初始化声音以便客户端进行连接而不回退到普通的 RDP？