Re: [LAD] mixing music and sound effects using libao

On Fri, 1 May 2015, Hermann Meyer wrote: Apparently using libao like this depends on the underlying driver being capable of doing mixing. Back to the drawing board... What I need to figure out boils down to a basic premise and two tasks: The premise: There are two buffers of audio which must be mixed. The tasks: 1) Add enough silent tracks to the audio chunk with fewer channels and get the tracks in the right places. 2) Cleanly mix two chunks of audio. I don't know how to do these. For the benefit of the curious, here's what I'm up to in greater detail: "Music" is played from OGG or MOD files[1]. "Sound-effects" are played from AIFF files. One music may be mixed with one sound-effect. No other mixing is allowed. My project[2] spawns a "mixer" thread on startup and waits for data to be put in a music buffer or a sound-effect buffer. For each sound effect or background music piece, a thread is spawned which decodes the audio file, fills the appropriate buffer, raises a semaphore, waits for an empty buffer, and repeats until done. They may told to stop early by setting bleep_playing or music_playing globals to FALSE. When the mixer gets its semaphore, it sets the ao_sample_format pointer appropriately, calls ao_open_live(), then plays the buffer with ao_play(). It then sets a semaphore indicating the buffer(s) are empty and goes back to sleep. The audio files can be of any legal sample size, sample rate, and channel count. Libsndfile, libmodplug, and libvorbis ensure that the data are all 16-bits at 44100 Hz. The next two steps are to add silent channels to the audio chunk with the smallest channel count and then to mix the results. I could use some help with these last two tasks. [1] Files are actually chunks embedded in a single IFF file. Another library, irrelevant to this discussion, gives me FILE pointers to what I want. [2] https://github.com/DavidGriffith/frotz -- David Griffith dave(a)661.org A: Because it fouls the order in which people normally read text. Q: Why is top-posting such a bad thing? A: Top-posting. Q: What is the most annoying thing in e-mail?