Looping a sound

A looped sound will repeat endlessly without any gap between its end and start. It is up to the sound artist to ensure that the end and start of the file match up however, otherwise there will be a "pop" as the waveform jumps from one shape to another.
 and detect looped sounds ONLY through cue points embedded in the file. This is a WAV-only feature, so MP3s cannot be looped. Microsoft ADPCM compressed WAVs can be looped, but due to the way they are encoded, there may a pop when the sound restarts if the sound is shorter than a few seconds.
== Looping a WAV ==
These free programs can add cue points to a WAV:
* GoldWave (trialware)
* Wavosaur (freeware)
* LoopAuditioneer (free and open source)
* OcenAudio (freeware)
* qaudio-cli (free and open source)
=== GoldWave ===
Open Goldwave and open the sound you want to loop. Click the cues icon. ()
Then in the new window click on the New button and add a cue point At Start. Then click New for another cue point and add a point At End. So it looks similar to this:
=== Wavosaur ===
==== Looping from beginning to end ====
* Open Wavosaur.
* Open the sound you want to loop.
* Go to Tools > Markers > Create marker, or press . This will add a new M0 marker at the beginning.
** If the marker is not at the beginning, move it there by dragging it with the mouse.
After that, click "Save" or "Save As".
==== Looping from anywhere in the file ====
# Open Wavosaur.
# Open the sound you want to loop.
# Go to Tools > Loop > Create loop points. It should create loop points.
## You can change their positions by dragging them.
## If you're looping a sound for , the end point should be moved at the end of the track, as end cues are not functional (see the Discussion page). You should trim the end instead.
## Double-clicking between the loop points will select the whole region between them and allow you to play it on loop.
Once you have found a satisfying position for the starting point:
# Click outside of the selection to clear it.
# Double-click the area between the loop points to select it.
## Do NOT play it now! Wavosaur uses the "playing position" to create markers.
# Go to Tools > Markers > Create marker, or press . This will add a new M0 marker at the exact position of the loop's starting point.
# Go to Tools > Loop > Delete loop points to clean up the unnecessary data. Failure to do so is inconsequential in Source, but will result in the track not looping in GoldSrc. 
After that, click "Save" or "Save As".
=== With a hex editor or script ===
 Bytes of a Cue Chunk of a WAV file
Bytes (hex)	as ASCII	as LittleEndianInteger	Description
63 75 65 20	"cue " 	 	begins a new cue chunk
1C 00 00 00	 	28 	size of this cue chunk in bytes(= the number of bytes that follow)
01 00 00 00	 	1 	number of cue points that follow now
 	 	 	
01 00 00 00	 	1 	ID of first (and only) cue point
00 00 00 00	 	0 	position(Wavosaur uses this as the cue point position)
64 61 74 61	"data" 	 	what kind of chunk this first cue point lies in
00 00 00 00	 	0 	chunk start
00 00 00 00	 	0 	block start
00 00 00 00	 	0 	sample position that Source uses to loop
Each WAV file consists of chunks where each chunk starts with an ID in ASCII, its size and more chunk-specific bytes. PCM waves typically consist of an format chunk, which describes how the audio samples are represented in bytes, and a data chunk, containing those bytes.
Loop points are defined in a separate cue chunk. The order of chunks in a file does not matter. That's why it is possible to simply append some bytes to the end of a non-looping WAV file to add a loop point. The following bytes represent a cue chunk that defines one cue point at the very first sample which makes Source loop it in its entirety:
<nowiki>63 75 65 20 1C 00 00 00 01 00 00 00 01 00 00 00 00 00 00 00 64 61 74 61 00 00 00 00 00 00 00 00 00 00 00 00</nowiki>
The last four bytes (the rightmost 00 00 00 00 in this case) represent a little endian integer which Source uses as the sample index at which the file should be looped. (Tested in: ) To set the loop point to the audio position at x seconds of a 44100 Hz mono or stereo file, represent x * 44100 in hexadecimal, reverse the byte order and use that instead of the above last four bytes. Example: To set the loop point at 2.6 seconds from the beginning, replace the last four bytes of the above with 2.6 * 44,100 = 114,660 = [1BFE4]_hex = [E4 BF 01 00]_le.
Now, to append some bytes to an existing WAV file, you can do the following.
==== Linux/MacOS ====
Create a file from the above bytes named cue.bin using the script below, then run cat my_nonlooping_sound.wav cue.bin > my_looping_sound.wav.
The following is a bash shell script used to generate cue.bin.
:
==== Windows ====
The following is a batch script file that appends the above bytes to the input files. Create a text file, paste the text in and save the file with the .bat extension. Drag-dropping non-looping WAV files on it (i. e. running the script with %1, %2, ... being the input files) will create looping copys ending with _loop.wav.
:
== Cue location ==
Your cues do not have to be at the start and end of the file. If you place them in the middle Source will start playing the sound normally, then when it reaches the end cue will loop back to the start cue. From then on only what's between the cues will play.
This can be used to give a sound a "winding up" effect that only plays once (e.g. a motor starting).
==Looping an MP3==
In , MP3 files can't be looped with start/end queues like a WAV. A can be a good workaround; have it start playing the sound again after it has fully played (or has played to the point desired).
This could also be done using User I/O from the ambient_generic to itself, and an input delay (another entity will still need to be used to trigger the initial input).
==See also==
* ambient_generic
* Sound and Music
==External links==
* Looping Menu Music - An Interlopers.net Tutorial on Soundlooping
Category:Sound System
Category:GoldSrc Sound System
Category:Third Party Tools