How to reproduce:
1. Open the attached project
2. Play in Editor or Build and run on iOS device
3. When video starts playing, change playback speed with slider
Result: sound of video mutes/disappears (output Audio Source)

Reproducible: 2017.1.0b5, 2017.1.0p2, 2017.2.0b5, 2017.3.0a2
Not reproducible: 5.6.3f1

DUT(reproducible):
iPhone 6, iOS 10.1
iPad mini 4, iOS 9.2.1
OSX 10.12.6

DUT(not reproducible):
137, Samsung Galaxy S8 [SM-G950F], 7.0.0, 1440x2960, Mali-G71
Windows 10

Videos(reproducible):
Groot_H264_AAC_480x360.mp4, 480x360 H264 avc Baseline@L3.1,30,545 kb/s,AAC/LC,2,129 kb/s,44.1kHz

Videos(not reproducible):
Groot_VP8_Vorbis_640x360.webm,640x360,VP8,30,651 kb/s,Vorbis,2,112 kb/s,44.1kHz