No sound on some video apps?

ipad 2, wifi only, 32gb using ios 5.01 and, updated 5.1

have several video playing apps (such tcm) that, when click watch video, not play sound. other apps, youtube, play sound. have looked , looked find wrong don't see anything.

have suggestions troubleshooting can audio?

 

in case helps, apps tcm app, retro tv, , movie vault silent.

keep looking don't have idea why have no audio. volume , if switch youtube, example, sound quite nicely.

thanks...

 

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