Bug 1195723: [flac] P12. Add sniffer for streaming flac. r=kamidphish

MozReview-Commit-ID: P62v6vsXzs

--HG--
extra : rebase_source : 37c365efbff607b10ad41ce8290556ded07783e2

dom/media/flac/FlacDemuxer.cpp

@@ -236,12 +236,42 @@ const uint8_t FrameHeader::CRC8Table[256] =
 class Frame {
 public:
 
-  // Find the next frame start in the current resource.
-  // On exit return true, offset is set and resource points to the frame found.
   // The FLAC signature is made of 14 bits set to 1; however the 15th bit is
   // mandatorily set to 0, so we need to find either of 0xfffc or 0xfffd 2-bytes
   // signature. We first use a bitmask to see if 0xfc or 0xfd is present. And if
   // so we check for the whole signature.
+  // aData must be pointing to a buffer at least
+  // aLength + FLAC_MAX_FRAME_HEADER_SIZE bytes.
+  int64_t FindNext(const uint8_t* aData, const uint32_t aLength)
+  {
+    uint32_t modOffset = aLength % 4;
+    uint32_t i, j;
+
+    for (i = 0; i < modOffset; i++) {
+      if ((BigEndian::readUint16(aData + i) & 0xfffe) == 0xfff8) {
+        if (mHeader.Parse(aData + i)) {
+          return i;
+        }
+      }
+    }
+
+    for (; i < aLength; i += 4) {
+      uint32_t x = BigEndian::readUint32(aData + i);
+      if (((x & ~(x + 0x01010101)) & 0x80808080)) {
+        for (j = 0; j < 4; j++) {
+          if ((BigEndian::readUint16(aData + i + j) & 0xfffe) == 0xfff8) {
+            if (mHeader.Parse(aData + i + j)) {
+              return i + j;
+            }
+          }
+        }
+      }
+    }
+    return -1;
+  }
+
+  // Find the next frame start in the current resource.
+  // On exit return true, offset is set and resource points to the frame found.
   bool FindNext(MediaResourceIndex& aResource)
   {
     static const int BUFFER_SIZE = 4096;
@@ -261,6 +291,7 @@ public:
       if (NS_FAILED(rv)) {
         return false;
       }
+
       if (read < FLAC_MAX_FRAME_HEADER_SIZE) {
         // Assume that we can't have a valid frame in such small content, we
         // must have reached EOS.
@@ -270,32 +301,12 @@ public:
       }
 
       const size_t bufSize = read + innerOffset - FLAC_MAX_FRAME_HEADER_SIZE;
+      int64_t foundOffset =
+        FindNext(reinterpret_cast<uint8_t*>(buffer.Elements()), bufSize);
 
-      const uint8_t* buf = reinterpret_cast<uint8_t*>(buffer.Elements());
-      uint32_t modOffset = bufSize % 4;
-      uint32_t i, j;
-
-      for (i = 0; i < modOffset; i++) {
-        if ((BigEndian::readUint16(buf + i) & 0xfffe) == 0xfff8) {
-          if (mHeader.Parse(buf + i)) {
-            SetOffset(aResource, offset + i);
-            return true;
-          }
-        }
-      }
-
-      for (; i < bufSize; i += 4) {
-        uint32_t x = BigEndian::readUint32(buf + i);
-        if (((x & ~(x + 0x01010101)) & 0x80808080)) {
-          for (j = 0; j < 4; j++) {
-            if ((BigEndian::readUint16(buf + i + j) & 0xfffe) == 0xfff8) {
-              if (mHeader.Parse(buf + i + j)) {
-                SetOffset(aResource, offset + i + j);
-                return true;
-              }
-            }
-          }
-        }
+      if (foundOffset >= 0) {
+        SetOffset(aResource, foundOffset + offset);
+        return true;
       }
 
       // Scan the next block;
@@ -1039,4 +1050,15 @@ FlacTrackDemuxer::TimeAtEnd()
   return mParsedFramesDuration;
 }
 
+/* static */ bool
+FlacDemuxer::FlacSniffer(const uint8_t* aData, const uint32_t aLength)
+{
+  if (aLength < FLAC_MAX_FRAME_HEADER_SIZE) {
+    return false;
+  }
+
+  flac::Frame frame;
+  return frame.FindNext(aData, aLength - FLAC_MAX_FRAME_HEADER_SIZE) >= 0;
+}
+
 } // namespace mozilla

dom/media/flac/FlacDemuxer.h

@@ -30,6 +30,9 @@ public:
     TrackInfo::TrackType aType, uint32_t aTrackNumber) override;
   bool IsSeekable() const override;
 
+  // Return true if a valid flac frame header could be found.
+  static bool FlacSniffer(const uint8_t* aData, const uint32_t aLength);
+
 private:
   bool InitInternal();
 

toolkit/components/mediasniffer/nsMediaSniffer.cpp

@@ -12,6 +12,7 @@
 #include "mozilla/ModuleUtils.h"
 #include "mp3sniff.h"
 #include "nestegg/nestegg.h"
+#include "FlacDemuxer.h"
 
 #include "nsIClassInfoImpl.h"
 #include <algorithm>
@@ -120,6 +121,11 @@ static bool MatchesMP3(const uint8_t* aData, const uint32_t aLength)
   return mp3_sniff(aData, (long)aLength);
 }
 
+static bool MatchesFLAC(const uint8_t* aData, const uint32_t aLength)
+{
+  return mozilla::FlacDemuxer::FlacSniffer(aData, aLength);
+}
+
 NS_IMETHODIMP
 nsMediaSniffer::GetMIMETypeFromContent(nsIRequest* aRequest,
                                        const uint8_t* aData,
@@ -179,6 +185,14 @@ nsMediaSniffer::GetMIMETypeFromContent(nsIRequest* aRequest,
     return NS_OK;
   }
 
+  // Flac frames are generally big, often in excess of 24kB.
+  // Using a size of MAX_BYTES_SNIFFED effectively means that we will only
+  // recognize flac content if it starts with a frame.
+  if (MatchesFLAC(aData, clampedLength)) {
+    aSniffedType.AssignLiteral(AUDIO_FLAC);
+    return NS_OK;
+  }
+
   // Could not sniff the media type, we are required to set it to
   // application/octet-stream.
   aSniffedType.AssignLiteral(APPLICATION_OCTET_STREAM);