In future, a sub class of GstMsdkEncClass may decide a native format by
using this method, e.g. JPEG encoder may accept YUY2 input, however the
current implemation needs a conversion from YUY2 to NV12 before encoding.
In addtion, a sub class may choose a format for encoding if the input
format is not supported by MSDK, e.g. the current implemation does
UYVY->NV12 if the input format is UYVY. We may do UYVY->YUY2 for JPEG
encoder in future
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