MP3
MP3 is a lossy-compressed audio file format used by all of Valve's engines, and is available in all first-party titles. While engine limitations prevent it from being used for everything that WAV files can be used for, its smaller file sizes make it suitable for non-looping music or incidental ambient sounds in a soundscape.
Warning:Using GoldSrc or Source 1's default implementation of MP3 in a commercial game requires paying for the Miles Sound System license. Consider implementing an alternative, such as Ogg Vorbis.Warning:- MP3s cannot be properly looped in
Source! Looping can be simulated by scripting replaying the sound via entity I/O or code scripting, but there will be a gap.
- In
Source 2, proper looping MP3s are possible (
only S&Box's tools can flag the VSND appropriately), but they can only loop in their entirety.
Recommended minimum bitrates
Unlike WAV, MP3 supports arbitrary bitrates, independent of sample rate and channel count. While this improves scalability, going below certain bitrates will result in noticeable quality degradation. Below are recommended minimum bitrates for the sample rates supported by Source ( Source 2 supports 
additional sample rates).
| Sample rate | Mono (1 channel) | Stereo (2 channels) |
|---|---|---|
| 11025 Hz | 32 kbps | 64 kbps |
| 22050 Hz | ||
| 44100 Hz | 64 kbps | 128 kbps |
Tip:These are just minimums. If you have the space to spare, you can go up to 320 kbps for higher quality audio! Setting the bitrate to double the values listed here will result in a less aggressive low-pass filter (at least in LAME).