Scream is a virtual device driver for Windows that provides a discrete sound device. Audio played through this device is published on your local network as a PCM multicast stream.
Receivers on the network can pick up the stream and play it through their own audio outputs. Two simple receivers for Linux (interfacing with PulseAudio or ALSA) and one for Windows are provided.
Scream is based on Microsoft's MSVAD audio driver sample code. The original code is licensed under MS-PL, as are my changes and additions. See LICENSE for the actual license text.
A ZIP file containing a signed x64 build is available on the GitHub releases page. The "installer" is a batch file that needs to be run with administrator rights.
The build is supposed to run on all x64 versions of Windows 7 through Windows 10.
Microsoft has recently tightened the rules for signing kernel drivers. These new rules apply to newer Windows 10 installations that were not upgraded from an earlier version. If your installation is subject to these rules, the driver will not install. Workaround: Disable secure boot in BIOS. For more information, see this issue.
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Linux/Pulseaudio: Not included in the installer package. Just type 'make' to build it. You might need to install build tools and Pulseaudio development packages.
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Linux/ALSA: Contributed by @ivan. Not included in the installer package. Just type 'make' to build it.You might need to install build tools and ALSA development packages.
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Windows: ScreamReader, contributed by @MrShoenel. Included in the installer package as of version 1.2.
All three receivers can be run as unprivileged users. Receiver systems that have an input firewall need to open UDP port 4010, or whatever custom port you use.
All audio played through the Scream device will be put onto the local LAN as a multicast stream (using unicast is optional - see below). Delay is minimal, since all processing is done on kernel level. There is no userspace portion.
The multicast target address and port is "239.255.77.77:4010". The audio is a raw PCM stream, always with two channels (stereo). The default sampling rate and size can be set as the "Default format" in the driver "Advanced" property page. Data is transferred in UDP frames with a payload size of max. 1154 bytes, consisting of 2 bytes header and 1152 bytes PCM data. The latter number is divisible by 4, 6 and 8, so a full number of samples for both channels will always fit into a packet. The first header byte denotes the sampling rate. Bit 7 specifies the base rate: 0 for 48kHz, 1 for 44,1kHz. Other bits specify the multiplier for the base rate. The second header byte denotes the sampling width, in bits. No magic necessary there.
Receivers simply need to read the stream off the network and stuff it into a local audio sink. The receiver system's kernel should automatically do the necessary IGMP signalling, so it's usually sufficient to just open a multicast listen socket and start reading from it. Minimal buffering (~ 4 times the UDP payload size) should be done to account for jitter.
To satisfy your audiophile feelings, or to reduce unnecessary resampling, you might want to set a higher sampling rate and/or sampling width. You can do that on the driver "Advanced" property page:
Tweak the registry in the manner depicted in this screenshot (you will have to create the "Options" key), then reboot:
Visual Studio and a recent WDK are required. Good luck!