Just got the Samsung Galaxy™ Stellar™ ..... Sometimes when I want to play a video or an audio in an app or on the web ... there is no sound ... however while there may be no sound for the video or audio file I still have sound for alerts such as text messages and email and notifications and such ....
I can get it back by restarting the phone .... I know I must be accidentally somehow muting but when I do I hve no idea how to un mute it ... unless I restart it
There is a separate sound profile for the different sound types (media, ringtones, alarms, in call volume) so that explains why you can hear notifications, even when media is muted. Also, the easiest way to change the different volume types is to use the volume rocker when that profile is active. If you can't hear a video, press volume up while it is playing.