One of our most common questions is "How do I record sound from YouTube or other streaming videos?" or "How can I copy audio from files that Audacity doesn't recognize?" The answer to both questions is to record the speaker output as the sound is playing. Unfortunately, this is not always as trivial as it first appears to be.
This is a common problem for Windows users due to the way audio drivers are written. It is up to the company providing the audio drivers to make this functionality easily accessible, but in many cases it is difficult or impossible for reasons we can only guess at.
So, putting aside any conspiracy theories or cries of incompetence, there are three different ways to record this kind of audio. Most convenient first:
1) Select it as an input in Audacity and click 'Record.'
Note: Macs do not have a built-in input for recording computer output. Skip to Methods 2 or 3 below if you are on a Mac.
Selection is normally done in the Mixer Toolbar selector (to right of the microphone symbol), but on Windows Vista it's always done in the Recording Device dropdown at Edit > Preferences > Audio I/O tab. Provided your audio drivers are written correctly and the operating system mixer is making the input available, you should be able to select a Recording Source called "Stereo Mix", "What U Hear", "Mix", "Loopback", "Sum" or something similar. It is up to the people writing the drivers to give this source a name, so it varies from driver to driver and we cannot give you an exhaustive list.
Once that source is selected, make sure "Software Playthrough" in the Audio I/O Preferences is turned OFF and Audacity will be set up to record everything coming out of your speakers (including Operating System sounds and any other inputs that are not muted).
If that doesn't work, then there's a chance you can activate that source by changing the settings through your Operating System's audio set-up software. For Windows users (both Vista and earlier systems), see this Wiki page: Using the Control Panel. On Linux using ALSA, see these instructions. If that is successful, exit and restart Audacity and you should be able to record your speaker output. If you still can't activate that source, then you will have to resort to method 2 or 3.
2) Plug in a "loop-back" cable.
Most Desktop and many Laptop users will be able to run a cable from their speaker output port (often coloured green) to a line-in port (often coloured blue) on their sound card and capture the speaker output that way. The exact cable you will need depends on how your sound card was manufactured, please consult your computer or sound card manual if you need help identifying the correct port. If you do not have a Line In port, skip to Method 3 below.
A typical computer speaker output port is driven at Line Level, so it's a perfect match for the Line In port that is also commonly found on sound cards. It is possible, but not necessary, to find a cable that will allow you to plug your speakers in as well so you can hear what you're recording. Plug the cable in, turn the computer's output volume up, open Audacity and go to the Mixer Toolbar input selector (or on Windows Vista, the Audio I/O tab of Preferences). Here, select "Line In" as your recording source. Again, make sure "Software Playthrough" is turned OFF as well. If you are on Mac, you may need to select "Line In" as default input at: Mac hard disk > Applications > Utilities > Audio MIDI Setup. On Windows, if you don't see "Line-In", follow this link to set "Line In" in the Windows Control Panel.
Now you will be able to record the computer's output. Adjust the input volume level in Audacity to make sure you aren't overloading the recording - since you might not be able to hear what's being recorded, this is an easy mistake to make.
3) Obtain new hardware or software.
The Behringer UCA202 is only $30, sounds nicer than built-in motherboard sound, and gives you a Stereo Mix option (as long as you update the drivers). This is not meant as an endorsement of that particular item, we've simply received many reports that it works nicely for this kind of recording. Another device that works well for this is Trust Sound Expert External.
You can also try using software "virtual audio drivers" to capture the computer playback. This usually means recording into some application other than Audacity, but you can still edit the recording in Audacity later. Freecorder is an example of a free virtual driver that will capture sound playing on the computer to an audio file; it works as a plug-in for Internet Explorer and other browsers.