Samantaz Fox AudricV kavin made a protobuf definition for the media header protobuf, that way we have it documented a bit (we still need to figure out a good place to write down our UMP information)
```protobuf
message UMPMedia {
    message ItagLastModified {
        required uint32 itag = 1;
        required uint64 last_modified_timestamp = 2;
    }

    required int32 unknown = 1;
    required string video_id = 2;
    required uint32 itag = 3;
    required uint64 last_modified_timestamp = 4;
    required uint64 range_start = 6;
    required ItagLastModified itag_last_modified = 13;
    required uint64 content_length = 14;
}
```