As you may know, the maximum supported resolution of VP8 codec is 1280x720.
The i.MX6 datasheet shows the following:
However, as a result of testing with several files(MKV, WebM), the VP8 codec with 1920x1080 resoltuion was also supported.
I tested video decoding using VPU on android 7.1 and Windows Embedded Compact 2013(WEC 2013) OS.
Use the VPU instead of SW type VP8 codec.
I hope this information will help you.
Have a nice day.