debugutils: Introduce videocodectestsink
This is a video specific sink used to test video CODEC conformance. This is similar to a combination of filesink and testsink, but will skip over any type of padding that GStreamer Video library introduces. This is needed in order to obtain the correct checksum or raw yuv data.
This element currently support writing back non-padded raw I420 through the location property and will calculate an MD5 and post it as an element message of type conformance/checksum. More output format or checksum type could be added in the future as needed.
The NV12 support is a simple speedup, so avoid NV12 to I420 relayout. It will write back NV12 into I420 non-padded file, and will compute the md5 sum as if the NV12 frame was layout in I420. The element does not make any guesses on pixel formats, so will simply won't negotiate if a unsupported formats is passed.