I use Opera 9.26 on Windows Vista 64bit and have had an issue viewing videos with the media player plug-in.
Following this guide, placing some files into the plugin folder in opera install directory solved my issue of media player not playing in my Opera browser.
SanDisk Ultra SDSSDHII-960G-G25 960 GB SATA III SSD (System)
Crucial MX100 CT256MX100SSD1 256GB SATA III SSD (User Tree)
2 * Seagate Barracuda 7200.12 ST31000528AS 1TB 7200 RPM SATA II Mech. HD
Seagate ST1500DL001-9VT15L Barracuda 7200.12 1.5 TB S
PSU
Thermaltake Black Widow TX TR2 850W 80+ Bronze Semi-Mod ATX
Case
ThermalTake Level 10 GT (Black)
Cooling
Corsair H100 (CPU, dual 140 mm fans on radiator) + Air (2 *
Mouse
Logitech MX Master (shared)
Keyboard
Logitech G15 (gen 2)
Internet Speed
AT&T Lightspeed Gigabit duplex
Operating System
Sabayon Linux (current, weekly updates, 5.1.x kernel)
Manufacturer/Model
Lenovo ThinkPad E545
CPU
AMD A6-5350M APU
Motherboard
Lenovo
Memory
8 GB
Sound Card
Conextant 20671 SmartAudio HD
Monitor(s) Displays
Lenovo 15" Matte
Screen Resolution
1680 * 1050
Hard Drives
INTEL Cherryvill 520 Series SSDSC2CW180A 180 GB SSD