While mining stone with a pickaxe (stone), all sound stopped, but the game continued. On inspection of the developer console, I saw the following error:

Error in class 'CodecJOrbis'
Unable to acquire inputstream in method 'initialize'.
ERROR MESSAGE:
minecraft:sound/hal4.ogg
STACK TRACE:
bhp.a(SourceFile:37)
bhx.a(SourceFile:34)
bhx.a(SourceFile:27)
biz.getInputStream(SourceFile:65)
paulscode.sound.codecs.CodecJOrbis.initialize(CodecJOrbis.java:281)
paulscode.sound.libraries.SourceLWJGLOpenAL.play(SourceLWJGLOpenAL.java:616)
paulscode.sound.Library.play(Library.java:706)
paulscode.sound.libraries.LibraryLWJGLOpenAL.quickPlay(LibraryLWJGLOpenAL.java:795)
paulscode.sound.SoundSystem.CommandQuickPlay(SoundSystem.java:1866)
paulscode.sound.SoundSystem.CommandQueue(SoundSystem.java:2438)
paulscode.sound.CommandThread.run(CommandThread.java:121)
Error in class 'SourceLWJGL OpenAL'
Audio Format null in method 'play'
Exception in thread "Thread-6" java.lang.NullPointerException
at com.jcraft.jorbis.Block.<init>(Block.java:55)
at paulscode.sound.codecs.CodecJOrbis.initialize(CodecJOrbis.java:252)
at paulscode.sound.libraries.SourceLWJGLOpenAL.play(SourceLWJGLOpenAL.java:616)
at paulscode.sound.Library.play(Library.java:706)
at paulscode.sound.Library.play(Library.java:675)
at paulscode.sound.SoundSystem.CommandPlay(SoundSystem.java:2076)
at paulscode.sound.SoundSystem.CommandQueue(SoundSystem.java:2599)
at paulscode.sound.CommandThread.run(CommandThread.java:121)

After the game was quit and restarted from the launcher, sound worked fine for a few minutes before the error was reproduced.