Issue #2357 - WebM demuxer can't tell when a video wants to be transparent.

Required to have an alpha channel (which in the strange world of graphics seems to refer to transparency, and not experimental code) in WebM videos. Straight port of Firefox 53 implementation, adapted slightly for a couple of patches previously taken without this.

Ref: BZ 1320829

dom/media/MediaData.cpp

@@ -340,6 +340,15 @@ MediaRawData::MediaRawData(const uint8_t* aData, size_t aSize)
 {
 }
 
+MediaRawData::MediaRawData(const uint8_t* aData, size_t aSize,
+                           const uint8_t* aAlphaData, size_t aAlphaSize)
+  : MediaData(RAW_DATA, 0)
+  , mCrypto(mCryptoInternal)
+  , mBuffer(aData, aSize)
+  , mAlphaBuffer(aAlphaData, aAlphaSize)
+{
+}
+
 already_AddRefed<MediaRawData>
 MediaRawData::Clone() const
 {
@@ -356,6 +365,9 @@ MediaRawData::Clone() const
   if (!s->mBuffer.Append(mBuffer.Data(), mBuffer.Length())) {
     return nullptr;
   }
+  if (!s->mAlphaBuffer.Append(mAlphaBuffer.Data(), mAlphaBuffer.Length())) {
+    return nullptr;
+  }
   return s.forget();
 }
 

dom/media/MediaData.h

@@ -622,15 +622,22 @@ private:
 class MediaRawData : public MediaData {
 public:
   MediaRawData();
-  MediaRawData(const uint8_t* aData, size_t mSize);
+  MediaRawData(const uint8_t* aData, size_t aSize);
+  MediaRawData(const uint8_t* aData, size_t aSize,
+               const uint8_t* aAlphaData, size_t aAlphaSize);
 
   // Pointer to data or null if not-yet allocated
   const uint8_t* Data() const { return mBuffer.Data(); }
+  // Pointer to alpha data or null if not-yet allocated
+  const uint8_t* AlphaData() const { return mAlphaBuffer.Data(); }
   // Size of buffer.
   size_t Size() const { return mBuffer.Length(); }
+  size_t AlphaSize() const { return mAlphaBuffer.Length(); }
   size_t ComputedSizeOfIncludingThis() const
   {
-    return sizeof(*this) + mBuffer.ComputedSizeOfExcludingThis();
+    return sizeof(*this)
+           + mBuffer.ComputedSizeOfExcludingThis()
+           + mAlphaBuffer.ComputedSizeOfExcludingThis();
   }
   // Access the buffer as a Span.
   operator Span<const uint8_t>() { return MakeSpan(Data(), Size()); }
@@ -661,6 +668,7 @@ protected:
 private:
   friend class MediaRawDataWriter;
   AlignedByteBuffer mBuffer;
+  AlignedByteBuffer mAlphaBuffer;
   CryptoSample mCryptoInternal;
   MediaRawData(const MediaRawData&); // Not implemented
 };

dom/media/MediaInfo.h

@@ -215,6 +215,7 @@ public:
     , mRotation(aOther.mRotation)
     , mBitDepth(aOther.mBitDepth)
     , mImageRect(aOther.mImageRect)
+    , mAlphaPresent(aOther.mAlphaPresent)
   {
   }
 
@@ -238,6 +239,16 @@ public:
     return MakeUnique<VideoInfo>(*this);
   }
 
+  void SetAlpha(bool aAlphaPresent)
+  {
+    mAlphaPresent = aAlphaPresent;
+  }
+
+  bool HasAlpha() const
+  {
+    return mAlphaPresent;
+  }
+
   nsIntRect ImageRect() const
   {
     if (mImageRect.width < 0 || mImageRect.height < 0) {
@@ -312,6 +323,9 @@ private:
   // mImage may be cropped; currently only used with the WebM container.
   // A negative width or height indicate that no cropping is to occur.
   nsIntRect mImageRect;
+
+  // Indicates whether or not frames may contain alpha information.
+  bool mAlphaPresent = false;
 };
 
 class AudioInfo : public TrackInfo {

dom/media/webm/WebMDemuxer.cpp

@@ -378,6 +378,7 @@ WebMDemuxer::ReadMetadata()
       mInfo.mVideo.mDisplay = displaySize;
       mInfo.mVideo.mImage = frameSize;
       mInfo.mVideo.SetImageRect(pictureRect);
+      mInfo.mVideo.SetAlpha(params.alpha_mode);
 
       switch (params.stereo_mode) {
         case NESTEGG_VIDEO_MONO:
@@ -656,6 +657,21 @@ WebMDemuxer::GetNextPacket(TrackInfo::TrackType aType, MediaRawDataQueue *aSampl
       WEBM_DEBUG("nestegg_packet_data failed r=%d", r);
       return NS_ERROR_DOM_MEDIA_DEMUXER_ERR;
     }
+    unsigned char* alphaData;
+    size_t alphaLength = 0;
+    // Check packets for alpha information if file has declared alpha frames
+    // may be present.
+    if (mInfo.mVideo.HasAlpha()) {
+      r = nestegg_packet_additional_data(holder->Packet(),
+                                         1,
+                                         &alphaData,
+                                         &alphaLength);
+      if (r == -1) {
+        WEBM_DEBUG(
+          "nestegg_packet_additional_data failed to retrieve alpha data r=%d",
+          r);
+      }
+    }
     bool isKeyframe = false;
     if (aType == TrackInfo::kAudioTrack) {
       isKeyframe = true;
@@ -713,10 +729,19 @@ WebMDemuxer::GetNextPacket(TrackInfo::TrackType aType, MediaRawDataQueue *aSampl
 
     WEBM_DEBUG("push sample tstamp: %ld next_tstamp: %ld length: %ld kf: %d",
                tstamp, next_tstamp, length, isKeyframe);
-    RefPtr<MediaRawData> sample = new MediaRawData(data, length);
-    if (length && !sample->Data()) {
-      // OOM.
-      return NS_ERROR_OUT_OF_MEMORY;
+    RefPtr<MediaRawData> sample;
+    if (mInfo.mVideo.HasAlpha() && alphaLength != 0) {
+      sample = new MediaRawData(data, length, alphaData, alphaLength);
+      if (length && !sample->Data() || (alphaLength && !sample->AlphaData())) {
+        // OOM.
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
+    } else {
+      sample = new MediaRawData(data, length);
+      if (length && !sample->Data()) {
+        // OOM.
+        return NS_ERROR_OUT_OF_MEMORY;
+      }
     }
     sample->mTimecode = tstamp;
     sample->mTime = tstamp;

layout/media/symbols.def.in

@@ -9,6 +9,7 @@ nestegg_duration
 nestegg_free_packet
 nestegg_init
 nestegg_offset_seek
+nestegg_packet_additional_data
 nestegg_packet_count
 nestegg_packet_discard_padding
 nestegg_packet_data