PhxDemo.Audio (phx_demo v0.1.1)

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Audio input for demos: PhxDemo.Steps.upload_audio/4, use_microphone/3, stop_microphone/1 and use_camera(path, audio: true).

Uploads go through the ordinary upload/4 (or drop_files/4); this module only adds the :audio_input timeline event. The simulated microphone is part of the JS stand-in in PhxDemo.Camera: getUserMedia({audio: ...}) returns a MediaStream from WebAudio (the fixture is decoded with decodeAudioData and played into a MediaStreamAudioDestinationNode). A request for {video, audio} gets both fake tracks.

Playback starts when the app requests the microphone, not when the step runs: the page's "record" button is what starts the voice, as with a real person. A non-looping fixture plays once, and a later request plays it again.

Formats

Anything ffmpeg decodes. WAV, MP3, Ogg, Opus and FLAC are served as they are (Chromium's decodeAudioData reads them); other formats (m4a, aac, wma, a video's soundtrack, ...) are converted to 16-bit WAV with ffmpeg and cached under the system temp dir, keyed by path, size and mtime.

Timeline

:audio_input events carry mode ("upload", "microphone" or "camera"), action, file (absolute path) and audible:

  • upload_audio: action: "upload", start is the event's at_ms (the moment the file was attached), duration_ms from ffprobe
  • use_microphone: action: "use" when the step runs, then action: "play" (with duration_ms and loop) each time the app starts listening, and action: "stop" for stop_microphone

PhxDemo.Render mixes the events with audible: true into the MP4.

Summary

Functions

classify(path)

:browser if the file is served as it is, :convert if ffmpeg converts it to WAV.

duration_ms(path)

Duration of an audio file in ms from ffprobe, or nil if it can't be read.

prepare!(path)

The path the browser can decode for a fixture: the file itself, or a cached WAV conversion. Raises ArgumentError if the file is missing or needs ffmpeg and it isn't installed.

soundtrack!(path)

The audio of a video as a cached WAV. Raises ArgumentError if the video has no audio stream.

Functions

classify(path)

:browser if the file is served as it is, :convert if ffmpeg converts it to WAV.

duration_ms(path)

Duration of an audio file in ms from ffprobe, or nil if it can't be read.

prepare!(path)

The path the browser can decode for a fixture: the file itself, or a cached WAV conversion. Raises ArgumentError if the file is missing or needs ffmpeg and it isn't installed.

soundtrack!(path)

The audio of a video as a cached WAV. Raises ArgumentError if the video has no audio stream.