AirPlay.Decoder (AirPlay v0.3.0)

Copy Markdown View Source

Stream-decode an audio file to AirPlay frames with bounded memory.

Runs ffmpeg as a port, reads its interleaved s16le stdout, slices it into 352-sample stereo frames, and hands them to AirPlay.Player on demand via take/2. The alternative — decoding the whole file to one PCM buffer (see AirPlay.Source.pcm/1) — costs ~2.4 GB for a 4-hour book; this keeps only a few seconds of frames around at a time.

Flow control comes from ffmpeg's -re flag (read input at its native rate), set by AirPlay.Source.stream_args/2: ffmpeg only produces PCM at ~1× real time, which is the same rate Player drains it, so the buffer neither floods the mailbox nor grows without bound.

Summary

Functions

await_ready(pid, min_frames \\ 16, timeout \\ 5000)

Wait until the decoder has buffered at least min_frames frames, or until ffmpeg exits before enough audio is available.

child_spec(init_arg)

Returns a specification to start this module under a supervisor.

start_link(opts)

Start a decoder. Options

stop(pid)
take(pid, n)

Take up to n buffered frames. Returns {frames, eos?}. frames may be shorter than n (or empty) if decoding is briefly behind; eos? is true once ffmpeg has finished and the buffer is drained.

Functions

await_ready(pid, min_frames \\ 16, timeout \\ 5000)

@spec await_ready(pid(), pos_integer(), timeout()) ::
  {:ok, non_neg_integer()} | {:error, term()}

Wait until the decoder has buffered at least min_frames frames, or until ffmpeg exits before enough audio is available.

child_spec(init_arg)

Returns a specification to start this module under a supervisor.

See Supervisor.

start_link(opts)

Start a decoder. Options:

stop(pid)

take(pid, n)

@spec take(pid(), non_neg_integer()) :: {[binary()], boolean()}

Take up to n buffered frames. Returns {frames, eos?}. frames may be shorter than n (or empty) if decoding is briefly behind; eos? is true once ffmpeg has finished and the buffer is drained.