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crossfade: New example for crossfading audio tracks using audiomixer

Submitted by Nirbheek Chauhan @nirbheek

Link to original bug (#752762)

Description

Created attachment 307971
crossfade: New example for crossfading audio tracks using audiomixer

/*

  • crossfade: An example application to play a list of audio files with
  • cross-fade between each file.
  • This example application uses the audiomixer element combined with
  • GstController and pad probes to play a list of audio files in such a way that
  • the audio is cross-faded while switching between files.
  • Each file is played by a decoder bin inside each CrossfadeItem. This bin has
  • a queue right before its srcpad which has a "max-size-time" of
  • 2 * CROSSFADE_TIME_MS. When an EOS is detected on the sinkpad of this queue,
  • the next CrossfadeItem is attached to audiomixer, the correct pad offset is
  • set, and fadein/fadeout is scheduled using GstControlSources.
  • A crossfade can also be scheduled immediately by switching to the next item
  • "early" using crossfade_app_activate_next_item_early().
  • The list of CrossfadeItems can be edited and added to dynamically; except the
  • currently-playing item and the next one (which has been prepared already).
  • Bugs:
    • If the size of the file being played is smaller than 3*CROSSFADE_TIME_MS
  • and the file was played with a fadein crossfade (i.e., it was not the first
  • file to be played), the queue before audiomixer which is used to detect a
  • file going EOS will contain buffers of a total time less than
  • CROSSFADE_TIME_MS. The crossfade will hence happen in whatever buffer-time
  • is available.
    • If CROSSFADE_TIME_MS is set to a value less than the duration of a single
  • buffer, no crossfade will happen, but the switch will be gapless.
    */

This is a decent example of how to use audiomixer for gapless/crossfade playback in an audio player. Although the example expects files, this method of doing crossfade/gapless should also work with arbitrary URIs.

Patch 307971, "crossfade: New example for crossfading audio tracks using audiomixer":
0001-New-example-for-audio-crossfade-using-audiomixer-and.patch