Prepare second decoder in advance to avoid buffering at end of ad breaks

Version

ExoPlayer 2.19.1

More version details

It can also be reduced on ExoPlayer 2.18.5.

Devices that reproduce the issue

Not device-specific.

Devices that do not reproduce the issue

No response

Reproducible in the demo app?

Yes

Reproduction steps

1. Add the sample below to the media.exolist.json file

{
        "name": "VMAP three empty midrolls, player buffer at ad points",
        "uri": "https://storage.googleapis.com/exoplayer-test-media-1/mkv/android-screens-lavf-56.36.100-aac-avc-main-1280x720.mkv",
        "ad_tag_uri": "https://run.mocky.io/v3/d3c23db8-aaf8-43a4-9690-3398a0f0f10f"
      }

2. Add log to Player.onPlaybackStateChanged(@Player.State int playbackState) callback at PlayerActivity.PlayerEventListener
3. Play the added sample video without seeking.

This issue can also be reproduced with the sample VMAP full, empty, full midrolls.

Expected result

The ad point plays seamlessly when there are no ads, and there is no lag.
At least it shouldn’t be lag every time.

Actual result

There is almost always an onPlaybackStateChanged buffer callback at the first(10s) and third(30s) ad point, which causes the playback to freeze briefly(around 1s).
The second ad point(20s) also has a buffer callback sometimes.

Media

https://storage.googleapis.com/exoplayer-test-media-1/mkv/android-screens-lavf-56.36.100-aac-avc-main-1280x720.mkv

Bug Report

• You will email the zip file produced by adb bugreport to android-media-github@google.com after filing this issue.