It's the snap making you decide whether you're OK with high volume. I think what might be happening here is that the snap causes a focus change on the media player, which stops playback and causes the active role to change.
** Attachment added: "snap.png" https://bugs.launchpad.net/indicator-sound/+bug/1504065/+attachment/4488405/+files/snap.png -- You received this bug notification because you are a member of Unity API bugs, which is subscribed to The Sound Menu. https://bugs.launchpad.net/bugs/1504065 Title: Cannot play videos when a wired headphone is connected Status in The Sound Menu: New Status in mediaplayer-app: New Status in unity8 package in Ubuntu: New Bug description: When having a wired headset connected to the device, video playback keeps on being paused as soon as playback is started. Looks like some snap-decision notification is shown, but it's too short time to read what it actually says because it disappears again when the playback stops again. To manage notifications about this bug go to: https://bugs.launchpad.net/indicator-sound/+bug/1504065/+subscriptions -- Mailing list: https://launchpad.net/~unity-api-bugs Post to : unity-api-bugs@lists.launchpad.net Unsubscribe : https://launchpad.net/~unity-api-bugs More help : https://help.launchpad.net/ListHelp