There are actually two parts to this question:
How can the application be informed of a decoding error in mfw_vpudecoder?
And much more importantly, how to force mfw_vpuencoder to immediately send a new key frame (aka Intra-frame) ?
When transmitting video over an Internet connection, packets get lost. If this happens the decoder fails and you can get artefacts in the picture. This remains until the next key frame refreshes the whole picture, which can be many seconds. To speed this up protocols such as SIP/H.323 have a fast update mechanism, but this requires that we can force the decoder to send a new key frame. This clears up the corrupted picture as soon as possible, improving the user experience.