embed avro data in an envelop

I am looking for some avro usage advice. We have created various schema
for different applications, say to represent, item id, name, metric,
etc. On the other hand our infrastructure group want to include some
meta data on all messages. This should include things like timestamp,
hostname, etc. This meta data is the same for all application messages.

One way to do it is to have a meta data schema that has timestamp,
hostname and a binary content field for the application data. This way
each message need to be decoded twice using two schema.

Another way is to somehow have a composite schema that include both the
meta data and the application specific data. So each message is just
decoded once and it automatically include the needed meta data. I wonder
if this can be done and if it is a good idea. Have other people
considered similar usage?

Wai Yip