Bug 757600 - Update the Opus version field parser. r=cpearce

On 2012 May 10, the Ogg encapsulation spec for Opus at
https://wiki.xiph.org/OggOpus bumped the version number
from zero to one. The one-byte field is also now notionally
split into major and minor subfields, with incompatible
changes signalled by the major field.

We update nsOpusState::DecodeHeader to parse the version
field separately from the stream identification and reject
any stream where the high four bits of the version field
is non-zero.

The opus-tools repo was updated 2012 May 22 to set with
version = 1. This commit enables playback of those files.

content/media/ogg/nsOggCodecState.cpp

@@ -818,7 +818,7 @@ bool nsOpusState::DecodeHeader(ogg_packet* aPacket)
   }
 
   // Otherwise, parse as the id header.
-  if (aPacket->bytes < 19 || memcmp(aPacket->packet, "OpusHead\0", 9)) {
+  if (aPacket->bytes < 19 || memcmp(aPacket->packet, "OpusHead", 8)) {
     LOG(PR_LOG_DEBUG, ("Invalid Opus file: unrecognized header"));
     mActive = false;
     return true;
@@ -826,6 +826,14 @@ bool nsOpusState::DecodeHeader(ogg_packet* aPacket)
 
   mRate = 48000; // The Opus decoder runs at 48 kHz regardless.
 
+  int version = aPacket->packet[8];
+  // Accept file format versions 0.x.
+  if ((version & 0xf0) != 0) {
+    LOG(PR_LOG_DEBUG, ("Rejecting unknown Opus file version %d", version));
+    mActive = false;
+    return true;
+  }
+
   mChannels= aPacket->packet[9];
   mPreSkip = LEUint16(aPacket->packet + 10);
   mNominalRate = LEUint32(aPacket->packet + 12);
@@ -860,7 +868,7 @@ PRInt64 nsOpusState::Time(PRInt64 granulepos)
 bool nsOpusState::IsHeader(ogg_packet* aPacket)
 {
   return aPacket->bytes >= 16 &&
-         (!memcmp(aPacket->packet, "OpusHead\0", 9) ||
+         (!memcmp(aPacket->packet, "OpusHead", 8) ||
           !memcmp(aPacket->packet, "OpusTags", 8));
 }