webamp/js/media

Audio Source Abstraction

An attempt to build a common interface for a media file source node. The goal is to have two implementations one that uses MediaElementAudioSourceNode and one that uses AudioBufferSourceNode.

See ./elementSource.js and ./bufferSource.js.

Interface methods

constructor(audioContext, destinationNode)

Construct a new instance:

const source = new Source(audoContext, context.destination);

disconnect()

Disconnect the source from the destination and clean up. The source cannot be reused.

loadFile(file)

Load a file supplied by the user from a <inpyt type='file'>.

Returns a Promise so that users can play when the file is done loading.

TODO: Throw if cannot play

loadUrl(url: string)

Load a url. Note that this URL is subject to CORS.

Returns a Promise so that users can play when the file is done loading.

TODO: Throw if cannot play

play()

Start playing the source.

• If already playing, start again at the begining.
• If paused, resume.
• If user has called seekToTime(), starts at that time.
• Has no affect if waiting.

Returns a Promise

pause()

• If already puased, does nothing.
• If stopped, does nothing.
• If waiting, puts us in paused mode.
• If playing, pauses the playback at the current time.

stop()

Stops playback, reverts the current time to 0.

seekToTime(seconds)

Updates the current time to seconds.

Does not change the current status. If already playing, media will continue to play from the new time.

getStatus(): STATUS

Get the current status. One of:

• "PLAYING"
• "PAUSED"
• "STOPPED"

getDuration(): seconds | null

Get the duration of the current track in seconds, or null if no track is loaded.

getStalled(): boolean

Are we buffering/loading?

getTimeElapsed(): seconds | null

How many secons have elapsed?

getNumberOfChannels(): number | null

getSampleRate(): number | null

getLoop(): boolean

setLoop(shouldLoop: boolean)

setAutoPlay(shouldAutoPlay: boolean)

on(EVENT: string, callback: () => {})

Subscribe to events

Options:

• "statusChange": Our play status has changed.
• "positionChange": Our position changed.
• "stallChanged": We either started or stopped stalling.

Manual test plan:

• Play a track on loop. Ensure the position indicator also loops.
• Pause a track after looping. Resume that track.
• Pause a track. Load a large file. Assert that the loading indicator shows.
• Pause a track. Resume it with play.
• Pause a track. Resume it with pause.
• Play a track. Part way through press play again. Asserrt that the track starts over.
• While a track is loading: Press play. Nothing should happen.
• Load a large file while another file is playing. Assert that the first file stops playing while we wait.