@dobey Yeah I got it a bit misleading, what I wanted to say is:
Hardware decoding will help only for those formats that were implemented at the time the device was released, logically hardware wont change with updates after that. On the other side, it could theoretically be some kind of ASIC or whatsoever that the vendor could load with new firmware so that it can learn new formats later.
So because we cannot load new proprietary codecs into firmware for the decoder ourselves we can just take whats either there in hardware or firmware. For some devices you will find the supported hardware codec lists somewhere.
If Google comes up with VP9, 10 whatsoever new shiny compression algorithm or your load your loved MKV movie onto the phone in both cases your screen might stay black with mediaplayer. If there is no suitable codec found, hardware or software, it wouldnt play. On the other hand, it could sometimes decode in software, but you notice the device getting hot, video could be stuttering etc.
Our older phones probably lack some decoders already,
@pavelprosto does that answer your case in some way?
