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DIY Wireless Audio Streaming By NICHOLAS VINEN Our CLASSiC DAC (February-May 2013) has a USB socket and can be connected to a PC, so you can play audio files on the computer through a hifi system with top-notch sound quality. But what if your hifi system isn’t in the same room as your computer? The answer is that you can use a small and cheap router to wirelessly stream audio between rooms. Here’s how. A FEW MONTHS AGO, we showed how to program a tiny, cheap router with some open source software so that it can act as a web server, control relays and do various other things (“Hacking a Mini Wireless Web Server”, November and December 2012). In this article, we will take a similar approach, configuring a slightly different router to stream CD-quality audio over WiFi to a USB audio device such as our CLASSiC DAC. There are several reasons why you would want to do this. First, if you’re listening to music with a reasonable dynamic range, you don’t want a computer with a fan or fans running in the same room; you will hear them during the quieter passages. Second, it’s much more convenient to select files to play from a hard disk than it is to dig through a collection of CDs, DVDs or other discs to find the one you want to play. And if you’ve bought music from iTunes or a similar service, you may not have physical media at all. In fact, just about anything you can play on your PC can be streamed to a remote sound system. 24  Silicon Chip If you have multiple computers in your home, they can be set up so that any one of them can stream audio to the hifi system using this approach. By the way, the unit we describe here is also suitable for streaming audio over wired Ethernet networks, if you already have the wiring and sockets in place. Commercial options There are products you can buy to do this job but they are generally not cheap and often have integrated amplifiers and speakers with mediocre sound quality. The aim of this article is to describe how to build your own network streaming solution and get the best possible audio quality but there are off-the-shelf solutions which will do the job too. If you would prefer to buy a commercial network audio player, one option is to get one with a digital output (TOSLINK or S/PDIF) and then you can connect it to the CLASSiC DAC to ensure the best sound quality. For Apple users, the easiest solution is to get a set of wireless speakers supporting the “Airplay” protocol. siliconchip.com.au Fig.2: setting a PC’s Ethernet interface for a static IP address in Windows 7. Change it back once you are finished. Fig.1: various Australian online shops sell the D-Link DIR412 router for less than $20. These are also available from overseas sellers via ebay or similar sites. Other options (with varying operating system support) include the Logitech Squeezebox, Netgear MP101, Marantz NA7004 with external Ethernet/WiFi bridge and the Sonos product range. Many of these cost over $200 though and while they will generally have more features than what we are describing here, we spent less than $20 on our router. In making that comparison, we’re assuming you’ve already built the CLASSiC DAC. Wireless performance To stream CD quality audio, you need a network link with a throughput of at least 1.5Mbps and it has to be pretty reliable – if the connection is dropping in and out regularly, the audio will break up. Modern WiFi products advertise speeds of 54Mbps, 108Mbps, 150Mbps and more. So it would seem like this is a lay-down misère. But there are various reasons why WiFi performance often falls well short of the advertised speeds and in some situations, it may be difficult to achieve the required speed. The two main reasons are spectrum congestion (ie, interference) and obstacles in the path of the microwaves. Congestion will depend on how many other people with WiFi networks and 2.4GHz cordless phones live in close proximity to you. If you are in a large apartment block or dense urban area, you will likely find dozens of WiFi networks when scanning with your computer. In this case, you should check that you can reach the required speed (eg, by copying a file to a laptop near your hifi system) before going ahead. 1.5Mbps is equivalent to roughly 200KB/s. If you are near a lot of WiFi networks, you may be able to improve the speed and reliability of the connection by changing the channel(s) your WiFi router operates on, to one of the less occupied channels. Changing the position of its external antenna(s) (if present) may also help. If buying a cordless telephone to use in a home with a WiFi network, it’s best to pick one that doesn’t operate at siliconchip.com.au Fig.3: the DIR412’s recovery page, accessed by holding in the reset button at power-up, lets you re-flash the unit via this web interface. Fig.4: after uploading a new image to the device, it takes about 90 seconds to reconfigure and reboot before you can connect to it. 2.4GHz. But note that WiFi networks can also operate at 5.17-5.825GHz (802.11a/n) so a 5.8GHz cordless phone isn’t necessarily the answer either! As for obstacles, walls and furniture are the most common and there isn’t much you can do about that but if the connection is marginal, you may find that slight changes in the position and orientation of the router(s) will make the difference. This is likely due to a combination of the antenna design (these days, often fractal) and standing waves caused by reflections off walls and other internal obstacles. Elevating the router may help, too. We tested streaming in two environments. The first was in a small office building with two other WiFi signals in range, with the main router inside a steel rack cabinet (near the top). The distance was about 10m with one plasterboard wall in the way. In this case, we got a reliable and July 2013  25 Fig.5: once OpenWRT has been loaded on the router, the next step is to set a root password via its web interface. it’s fine for transmitting audio over Ethernet as long as you disable its WiFi altogether. As a result, we bought a D-Link DIR-412 instead, in the hope that its slightly different hardware would not have the same bug. Getting it up and running is a bit more difficult since it isn’t as popular as the WR-703N and thus OpenWrt has no official support for it. But we did eventually get it working and were relieved to find its audio output is clean, even when streaming over WiFi. The steps required to set up a DIR-412 for WiFi audio streaming are listed below. This unit is available from local and overseas retailers at a similar price to the WR-703N. At the time of writing, it was available from five different Australian online retailers for less than $20 (not including postage) – see Fig.1. One of the great things about the DIR-412 is that it has a reset button which can be used to activate an emergency recovery mode, allowing you to re-flash it even if you have accidentally “bricked” it. In theory, any wireless router with USB ports and OpenWrt support can be used for this project – see http://wiki. openwrt.org/toh/start But the DIR-412 is the model that we know will work so we’re going to stick with it. Problems with OpenWrt Some readers who re-flashed a router using the steps outlined in our previous articles (mentioned earlier) ran into problems. We believe these are sorted out now. Check the panel later in this article for details on what went wrong and for the solutions. Preparing the router Here are the steps to set up the DIR-412 for wireless audio streaming. (1) Download the two required OpenWrt images. These are available from http://downloads.openwrt.org/attitude_adjustment/12.09/ramips/rt305x/ and have the following file names: openwrt-ramips-rt305x-dir-615-d-squashfs-factory.bin openwrt-ramips-rt305x-wr512-3gn-4M-squashfs-sysupgrade.bin Fig.6: enter the device’s IP address, the user name “root” and the password you have set into a Secure Copy (SCP) program to copy the WiFi firmware off the device. consistent connection of around 20Mbps, giving flawless audio streaming. The second environment was a medium-sized apartment building with about 10 WiFi networks in range and a brick wall between the two routers. The main router used was an older model with a single external antenna and was placed on a desk. In this case, speed was not an issue but we had to play with the position of the receiving unit to get a reliable connection with no drop-outs. Our approach We first tried setting up audio streaming via the TPLink WR-703N that we featured in our earlier articles on router “hacking”. It did work but not reliably. With this unit, when WiFi is enabled, USB audio has intermittent clicks and pops, suggesting USB data packet corruption. That rules that unit out for wireless streaming although 26  Silicon Chip (2) Connect power to the DIR-412 while holding down the recessed reset button at the rear, eg, with a paper clip. Release it after about 10 seconds and the power LED should be flashing orange. (3) Temporarily disconnect your LAN cable (if present) and connect the DIR-412’s Ethernet port to your PC; you can use the supplied cable. (4) Set your computer to use a static IP address of 192.168.0.2. In Windows 7, this can be done by going to the Network and Sharing Centre (accessible via the Control Panel), clicking “Change adapter settings”, double clicking your Ethernet adaptor, clicking Properties, then doubleclicking on the TCP/IPv4 entry – see Fig.2. Select “Use the following IP address” and enter 192.168.0.2 with a subnet mask of 255.255.255.0, then click “OK” several times to close the remaining dialogs. Other versions of Windows use a similar procedure. (5) Point a web browser to http://192.168.0.1 (ie, type that in the address bar) and you should get a screen like Fig.3. siliconchip.com.au Fig.7: after connecting to the DIR412 using WinSCP, navigate to the firmware directory (at right) and copy the RT305X.eeprom file to a temporary location on your PC (left). This is necessary as there is no official OpenWRT image available for the DIR-412 and doing so allows us to get USB and WiFi both working at the same time. If not, check that the DIR-412 is in emergency recovery mode (ie, flashing orange power LED) and check that the IP is set correctly (eg, run “ipconfig” in a command prompt) and the Ethernet cable is plugged in correctly at both ends. (6) Click the “Select” button and then browse to the first file you downloaded earlier, for the DIR-615 router. (7) Click the “Proceed” button and you should then get a screen similar to Fig.4. Don’t touch any of the cables to the DIR-412 during the 90-second countdown as the unit is re-flashed. (8) Change your computer’s IP address to 192.168.1.2 using the same procedure as in step 4. (9) Point your browser at http://192.168.1.1 and you should get the LuCI login screen (Fig.5). Click the “login” button. (10) Click the link at the top of the screen to set a password, then enter your chosen password in both boxes and click the “Save & Apply” button in the bottom corner. (11) Use an SCP program such as WinSCP to log into the router with the user name “root”, your chosen password and an IP address of 192.168.1.1 (Fig.6). When you get a warning about the server’s host key not being found, click “Yes” to proceed. You may also get a message “Error getting name of current remote directory”; click OK to ignore it. Copy the file /overlay/lib/firmware/RT305X.eeprom to your PC. To find this, you may need to double-click the “..” entry first – see Fig.7. (12) Go back to the web interface, click the “System” tab at the top, then the “Backup / Flash Firmware” tab that appears below it. Near the bottom of the screen, under “Flash new firmware image”, click on the Browse button and choose the second OpenWrt file you downloaded, for the WR512-3GN router (Fig.8). Click the “Flash Image” button and it will verify that the file is valid (Fig.9); click the button to proceed with re-flashing. siliconchip.com.au (13) Wait about 90 seconds and the web interface should automatically re-load; if not, re-enter http://192.168.1.1 in your browser address bar. You will need to log back in. (14) Use SCP to copy the RT305X.eeprom file back onto the reflashed router, over the top of the file in /overlay/lib/firmware. If asked whether to overwrite the existing file, select “Yes”. (15) Go to the System tab on the web interface, then click on the Reboot sub-tab under it at right and then click the “Perform reboot” link. (16) Once it has rebooted, log back into the web interface. Click on the Network tab, then the WiFi sub-tab. Enable WiFi using the button labelled as such and the wireless LED on the router should turn green. Click “Scan”. You should get a list of nearby wireless networks (Fig.10). Click the appropriate “Join Network” button and enter the password and other details required to access your network. Select the “lan” firewall zone (green), click the “Submit” button and then “Save & Apply” at the bottom. (17) Wait about 20 seconds, then click on the Interfaces sub-tab near the top of the screen and check that “WWAN” is shown with a green background. If you have DHCP on your network (most people do), the unit should have picked up an IP address which will be shown to the right, under IPv4 and it will normally start with “192.168”. Make a note of this IP. Also go to the “Status” tab and write down the Netmask, Gateway and DNS addresses under “Network”. (18) Under Interfaces, click on the button to edit this WWAN interface (at right) and then change “DHCP client” to “Static address”. Click “Switch protocol”, and in the “IPv4 address” box which appears, enter the address you want to assign to the router. It should be the same as the address you noted in the last step except for the final number. You need to choose this number carefully so that it can’t conflict with another device which has its IP address allocated automatically by the main router via DHCP. That July 2013  27 (19a) Click on the Interface sub-tab again. What you do next depends on whether you will be connecting the router to Ethernet or just using wireless. (19b) Wireless only: compare the IPv4 addresses for LAN and WWAN. If they have the same first three digits (eg, both start with 192.168.1) then you will need to change the LAN IP address or else wireless will not work with the Ethernet cable unplugged. Click on the Edit button to the right of the LAN interface, change the second-last digit in its address, then click the Save & Apply button. Make a note of this new address since if you lose access to the wireless network, you will need to use this address to access the router; if all else fails, you can always use the emergency recovery mode. (19c) Wired and wireless: pick another address similar to what you assigned to the wireless interface but not the same (eg, 192.168.0.201) and assign this to the LAN interface, using a similar procedure as in step 19b. Note that in this case, if the unit is not connected to an Ethernet network, the WiFi interface will be inoperative. Fig.8: use the Flash operations tab to replace the current firmware image with one that has USB support. router will assign DHCP addresses with a range of numbers, typically ending in a number between 10 and 100. Higher numbers are generally safe, eg, between 200 and 250. If in doubt, check your main router configuration. Also enter the Netmask, Gateway and DNS addresses that you noted earlier, then save and apply the changes. Fig.9: after uploading the new image, you’re asked to verify that it is correct and you want to proceed. If you use the file we specified, your checksum should match ours. 28  Silicon Chip (20) Unplug the Ethernet cable from the D-Link DIR-412 router and your PC, then re-connect your PC to its usual network (if a cable was plugged in before). If you will be using the DIR-412 with a wired connection, connect the Ethernet cable. (21) On your PC, point a browser at the IP address you have assigned to the wireless network of the DIR-412, eg, http://192.168.0.200 You should then be able to log into the web interface as before. This confirms that the wireless interface is working properly. Fig.10: once the new WiFi firmware is in place, you can perform a Wireless Scan and then find and connect to your WiFi network. siliconchip.com.au Fig.11: this is the greeting screen after connecting to OpenWRT with a Secure Shell (SSH) program. You can then install extra software and set it up using text commands. (22) Use an SSH program such as PuTTY (Windows) or OpenSSH (Linux/Mac) to login as root at this same IP address, using the same password as for the LuCI web interface. Again, we described how to do this in the November 2012 issue but if you install and run PuTTY, it should be pretty easy to figure out. You should then get a text greeting screen as shown in Fig.11. (23) Type the command “opkg update” and press enter. It will then download the list of available packages from the internet with the message “Updated list of available packages ...”. If you get an error message instead, that suggests the gateway and/or DNS addresses entered earlier are wrong; correct them via the web interface and try again. (24) Once this list has updated, type opkg install netcat kmod-usb-audio and press enter. This installs the USB audio driver and a program to stream data over a TCP/IP network. (25) To check that USB audio is working, plug the CLASS­ iC DAC or a USB audio dongle into the port on the top of the router and then type cat /proc/asound/cards. You should get a result something like this: Fig.12 (above): VLC is a media player that’s available for multiple operating systems, including Windows. It can play audio to a file on disk which we then stream over the wireless network. Fig.13 (left): a shortcut like this can then be used to launch the software and start streaming audio at any time. 0 [CODEC ]: USB-Audio – USB Audio CODEC Burr-Brown from TI USB Audio CODEC at usb-dwc_otg.0-1, full speed Check that it is installed correctly by typing aplay -h – you should get a long help text. Otherwise, one of the above files may not have been copied correctly. (26) Now for the audio playback software. This comes in packages with other software we don’t want and which won’t fit in flash. So we install them to a temporary location in RAM and then copy just the required files into flash. To do this, type opkg install -d ram alsa-utils and press Enter. Several packages will be downloaded and installed. Then, type the following series of commands: (27) By default, audio played will be resampled to 48kHz. But if you are mostly playing music from CDs, then these will be 44.1kHz so to get the best audio quality, we want to change this default rate. This can be done with the following command: sed -i s/48000/44100/ /usr/share/alsa/alsa.conf Confirm this worked by running grep 44100 /usr/share/alsa/ alsa.conf and you should see: defaults.pcm.dmix.rate 44100 cp /tmp/lib/libpthread-0.9.33.2.so /tmp/lib/librt-0.9.33.2.so /lib cd /lib ln -s libpthread-0.9.33.2.so libpthread.so.0 ln -s librt-0.9.33.2.so librt.so.0 cp /tmp/usr/lib/libasound.so.2.0.0 /usr/lib cd /usr/lib ln -s libasound.so.2.0.0 libasound.so.2 cp /tmp/usr/bin/aplay /usr/bin cp -R /tmp/usr/share/alsa /usr/share (28) We are now ready to set up the streaming audio receiver. This can be done with the following command (be careful to type it exactly and only press enter at the end): siliconchip.com.au echo ‘while [ 1 ]; do netcat -l -p 44100 | aplay -B 100000 -r 44100 -c 2 -f S16_LE -t raw -; done &’ > /etc/rc.local Then to get it going, make sure the USB audio device is plugged in and then type this command: source /etc/rc.local This will happen automatically each time it boots from now on. July 2013  29 Problems With The WR-703N Router & OpenWRT W E GOT AN enthusiastic response to our articles on re-flashing the WR703N mini router (“Hacking A Mini Wireless Web Server”, November & December 2012). Unfortunately though, some readers who purchased a WR703N and attempted to re-flash it ran into problems. There were two different reasons for this. The first is that late last year, the manufacturers of the WR703N brought out a new version of the device (v1.7) that worked a bit differently from the previous version. Specifically, its bootloader software disables the Ethernet port on boot and relies on the main program to re-enable it, something that was not necessary with earlier versions of the device. Note that many of the affected devices have a sticker on the bottom incorrectly showing the version as 1.6. The OpenWRT software has since been patched to fix this (ie, enable Ethernet on boot), so if you buy one of these routers now and attempt to flash it, it should work. But those people who flashed their units before this fix was released (right at the end of 2012/beginning of 2013) were left unable to connect to it via either Ethernet, which was disabled, or WiFi, which needs to be set up before it can be used. In this case, the only solution is to solder a serial port connector to three small pads on the PCB, as shown here: http://forums.openpilot.org/blog/52/entry-92-unbrickwr703n-wifi-router/ You can then change settings or re-flash the unit via a serial console, as described on that web page. More information on the Ethernet boot problem can be found at https://forum.openwrt.org/viewtopic. php?id=40986 New versions of OpenWRT Another problem that some readers encountered was that they were unable to install certain packages using the opkg program, mainly those starting with kmod. The problem is that OpenWRT was a work in progress last year when we published the articles describing how to re-flash the WR703N. After you had re-flashed your unit, there was the possibility that changes to the software on the OpenWRT website would render the available packages incompatible The DIR-412 is now ready to receive audio. Check that the USB audio device is plugged into it and move on to setting up your PC. Streaming to it To send audio to the unit, it’s simply a matter of making a TCP connection on port 44,100 and sending a WAV file containing the PCM audio data. That sounds easy but we couldn’t easily find Windows music players with this sort of capability so we’ve come up with a small program which allows you do this. It’s called “TCPWAVStream” and we are making the source code and Windows executable file available for download. It also builds and runs on Linux (make sure gcc and binutils are installed, then run make). It will probably work in Mac OSX too, since that is based on BSD. However, we haven’t actually tried to compile it on a Mac. This software can work in one of two ways. The simplest is to use a music/video player such as VLC. You can 30  Silicon Chip with the now out-of-date version of the firmware on your router. In fact, the version of the software that we recommended using, Attitude Adjustment, has now been finalised with version 12.09 and they have started work on a new version called Barrier Breaker. Because we recommended installing OpenWRT from the “trunk” repository, that means that when they switched over from Attitude Adjustment to Barrier Breaker, it became virtually impossible to install kernel module packages as it would try to download files for the wrong version. If you have this problem, you have two options: either reflash your router with the latest version of Attitude Adjustment or move over to Barrier Breaker. In general, we recommend sticking with the former solution as it means you are far less likely to run into this same module compatibility problem in future although Barrier Breaker has some new features which some people may wish to experiment with. Either way, the procedure is similar. For Attitude Adjustment, download the latest sysupgrade firmware from this location: http://downloads.openwrt.org/attitude_adjustment/12.09/ar71xx/generic/openwrt-ar71xx-generic-tlwr703n-v1-squashfs-sysupgrade.bin For Barrier Breaker, it can be found here: http://downloads.openwrt.org/snapshots/trunk/ar71xx/ openwrt-ar71xx-generic-tl-wr703n-v1-squashfs-sysupgrade.bin Use the procedure described in this article (step 12) to re-flash the router with this new firmware. Note that you may need to re-install any packages you installed previously with opkg after doing this. Note also that you may already have Barrier Breaker if you used the instructions we published previously after the trunk had been switched over. And if you do, some of the packages that we explained you should install in those articles may not be necessary. For example, kmod-usbstorage may already be present and not required to access a USB flash drive that’s plugged into the router. download the Windows version for free from http://www. videolan.org/vlc/download-windows.html Once VLC is installed, you then set it up to output sound to a WAV file. To do this, go to Tools -> Preferences -> Audio and then change the Output module to “File audio output”. Select a destination file on a drive with plenty of free space. We set ours to c:\temp\temp.wav (see Fig.12; the directory c:\temp must exist). You will then need to re-start VLC for this to take effect. Download and unzip TCPWAVStream.exe and cygwin1.dll to a convenient location (eg, C:\Program Files), then create a shortcut to the exe file on your desktop, or wherever you prefer. Right-click on this shortcut, then select “Properties” and change the Target field to add a space at the end, then the name of your WAV file in quotes, then another space and then the IP address of the router to stream to. In our case, the Target field then contains (see Fig.13): “C:\Program Files\TCPWAVStream.exe” “c:\temp\temp.wav” 192.168.0.200 siliconchip.com.au Double-click this shortcut and it should open a text box. Now play a file in VLC and you should see the buffer fill up, as indicated by an increasing buffer percentage (Fig.14). Once the buffer reaches about 70% full, assuming your router is switched on and ready, the program will open a connection and start streaming audio to it. When this happens, the buffer percentage should drop to about 50% and hover around that. Meanwhile, the lights on the router will flash to indicate constant data reception and audio playback should begin. Confirm this by listening to the DAC’s output. To stream audio in future, assuming the wireless router is powered on, you just need to launch that shortcut and then play the file(s) in VLC. Another option If you want to use other audio software which doesn’t have a WAV writer feature, there is another option. Download and install the latest version of the “Virtual Audio Capture Grabber Device” from http://sourceforge.net/ projects/virtualaudiodev/files/ This software essentially allows you to record whatever is being played from your PC, ie, it is a loopback device. You can then feed this recorded audio to our streaming software. Then anything you play on your PC will also be sent to the router and thus to your hifi system. We don’t know for sure whether this is a purely digital path or whether noise and distortion can be introduced by this process but it sounds reasonably clean. Once you have installed the device, you can then create a shortcut to start up the streaming. Navigate to the directory where is has installed ffmpeg.exe. In our case, this is the following rather long path: C:\Program Files (x86)\Virtual Audio Capture Grabber\screencapture-recorder-to-video-windows-free\configuration_setup_ utility\vendor\ffmpeg\bin You will then need to create a batch file (eg, TCPWAVStream. bat) to initiate streaming. This should contain the following, which you will need to adjust depending on where your ffmpeg.exe and TCPWAVStream.exe files are located: cd “C:\Program Files (x86)\Virtual Audio Capture Grabber\screencapture-recorder-to-video-windows-free\configuration_setup_ utility\vendor\ffmpeg\bin” ffmpeg -f dshow -i audio=virtual-audio-capturer -acodec pcm_s16le -f wav -loglevel panic - | “c:\Program Files\TCPWAVStream.exe” 192.168.0.200 You can do this by typing those lines into notepad (note: just two lines, one starting with “cd” and one with “ffmpeg”) and then saving it as a file with a .bat (batch file) extension. Run this .bat file and you should get a result similar to that described above although since this will be constantly capturing audio whether or not you are playing anything, it should begin buffering immediately. Direct streaming You can also use ffmpeg to decode and stream audio files direct to the router without going through your system’s sound card or a temporary file but you will need to use the command line to play back files. All you need to do is use the ffmpeg command above but get rid of the -f dshow and -i audio=virtual-audio-capturer parameters and replace them with the name and path of the file to be played. This works in Linux too but is really only appropriate siliconchip.com.au Fig.14: our simple program runs in a command prompt box and streams audio data when you are playing a file. for advanced users who are comfortable with a command line interface. How our software works While the TCPWAVStream program is rather elegant in its operation (we think), it is still rather complex and we won’t go into great detail here – if you’re interested, have a look at the source code. But in brief, what it does is constantly read from the end of the file specified (or standard input) into a circular memory buffer while also emptying that buffer to a TCP “socket” which sends the data to the router. The WAV header contains the audio format details (sampling rate, etc) and the router thus configures its audio output to match that of your PC. Because the router only consumes the data from its socket at its internal sampling rate, this effectively throttles the emptying of the buffer. While the sampling rate of the playback from your PC will in theory match that of the audio device attached to the router, in practice they will never be exactly the same as they are using different crystals to derive the sampling rate. This means that the memory buffer in the PC software will slowly fill or empty over time. The software attempts to keep the fill to about 50% by slightly shortening or lengthening any periods of silence in the data it streams. The software gracefully handles situations such as the WAV file being deleted or truncated (which is what happens when VLC starts playing a different file), the connection to the router being dropped or the router being temporarily unreachable and so on. Note that it will delete the WAV file once it has finished reading it, if it remains unchanged for a short period, so you should only point it at temporary files. Also note that because there are multiple layers of buffering – ie, in VLC/Virtual Audio Grabber, the file system, the TCPWAVStream software, the network buffers on both ends, in the audio player on the router, its USB hardware and in the USB device itself – there will be quite a delay between starting or stopping playback and a change actually occurring at the output. This will be of the order of a couple of seconds. This isn’t normally a problem when playing music but if you want to stream the audio from a video, you will need to change the A/V synchronisation delay or else the audio and video will not match up. With VLC, this can be done using the “j” and “k” keys on your keyboard. Other video playback software may or may not have this capability. If you experience audio dropouts in the audio while streaming, the likely cause is an unreliable WiFi link. Refer to the section on wireless performance for information on SC likely methods to correct this. July 2013  31