* Initialize the FFTextReader from the given AVIOContext. This function will
* read some bytes from pb, and test for UTF-8 or UTF-16 BOMs. Further accesses
* to FFTextReader will read more data from pb.
* Initialize the FFTextReader from the given AVIOContext. This function will
* read some bytes from pb, and test for UTF-8 or UTF-16 BOMs. Further accesses
* to FFTextReader will read more data from pb.