Issue description

When trying to play a gapless playback between two MP3 files, a noticeable gap is detected between them.
The issue is also reproduced when using Exoplayer demo app with the test.mp3 file already added in assets.
I added the following snippet to PlayerActivity in Exoplayer demo app L299 for test purpose => the issue is reproduced : a gap between the two media sources is heard.

    val concatenatingMediaSource = ConcatenatingMediaSource()
    val defaultMediaSourceFactory = DefaultMediaSourceFactory(context)
    concatenatingMediaSource.addMediaSource(defaultMediaSourceFactory.createMediaSource(
        MediaItem.fromUri("asset:///test.mp3")))
    concatenatingMediaSource.addMediaSource(defaultMediaSourceFactory.createMediaSource(
        MediaItem.fromUri("asset:///test.mp3")))
    player.setMediaSource(concatenatingMediaSource)
    player.prepare()

Please notice that the delay/padding information is well detected by Exoplayer for the test.mp3 in demo app assets.

• ExoPlayer version number : 2.13.0
• Android version : Android 7 & Android 10
• Android device: Samsung galaxy s7 edge & Samsung galaxy s10

Please let me know if you need more details.
Thank you