media/vpx: Add support for VP9 alpha channel

media/filters/vpx_video_decoder.cc

Index: media/filters/vpx_video_decoder.cc
diff --git a/media/filters/vpx_video_decoder.cc b/media/filters/vpx_video_decoder.cc
index 40814bb273ad5a3f5cc18e96ea9172f9fd4e929b..bf029cc0da3c5d53eb4d3a3571e234cc46aa0970 100644
--- a/media/filters/vpx_video_decoder.cc
+++ b/media/filters/vpx_video_decoder.cc
@@ -136,19 +136,20 @@ class VpxVideoDecoder::MemoryPool
   int NumberOfFrameBuffersInUseByDecoder() const;
   int NumberOfFrameBuffersInUseByDecoderAndVideoFrame() const;
 
- private:
-  friend class base::RefCountedThreadSafe<VpxVideoDecoder::MemoryPool>;
-  ~MemoryPool() override;
-
   // Reference counted frame buffers used for VP9 decoding. Reference counting
   // is done manually because both chromium and libvpx has to release this
   // before a buffer can be re-used.
   struct VP9FrameBuffer {
     VP9FrameBuffer() : ref_cnt(0) {}
     std::vector<uint8_t> data;
+    std::vector<uint8_t> alpha_data;
     uint32_t ref_cnt;
   };
 
+ private:
+  friend class base::RefCountedThreadSafe<VpxVideoDecoder::MemoryPool>;
+  ~MemoryPool() override;
+
   // Gets the next available frame buffer for use by libvpx.
   VP9FrameBuffer* GetFreeFrameBuffer(size_t min_size);
 
@@ -380,11 +381,11 @@ bool VpxVideoDecoder::ConfigureDecoder(const VideoDecoderConfig& config) {
     return false;
 
   // These are the combinations of codec-pixel format supported in principle.
-  // Note that VP9 does not support Alpha in the current implementation.
   DCHECK(
       (config.codec() == kCodecVP8 && config.format() == PIXEL_FORMAT_YV12) ||
       (config.codec() == kCodecVP8 && config.format() == PIXEL_FORMAT_YV12A) ||
       (config.codec() == kCodecVP9 && config.format() == PIXEL_FORMAT_YV12) ||
+      (config.codec() == kCodecVP9 && config.format() == PIXEL_FORMAT_YV12A) ||
       (config.codec() == kCodecVP9 && config.format() == PIXEL_FORMAT_YV24));
 
 #if !defined(DISABLE_FFMPEG_VIDEO_DECODERS)
@@ -400,9 +401,10 @@ bool VpxVideoDecoder::ConfigureDecoder(const VideoDecoderConfig& config) {
   if (!vpx_codec_)
     return false;
 
-  // Configure VP9 to decode on our buffers to skip a data copy on decoding.
+  // Configure VP9 to decode on our buffers to skip a data copy on
+  // decoding. For YV12A-VP9, we use our buffers for the Y, U and V planes and
+  // copy the A plane.
   if (config.codec() == kCodecVP9) {
-    DCHECK_NE(PIXEL_FORMAT_YV12A, config.format());
     DCHECK(vpx_codec_get_caps(vpx_codec_->iface) &
            VPX_CODEC_CAP_EXTERNAL_FRAME_BUFFER);
 
@@ -470,8 +472,26 @@ bool VpxVideoDecoder::VpxDecode(const scoped_refptr<DecoderBuffer>& buffer,
     return false;
   }
 
-  if (!CopyVpxImageToVideoFrame(vpx_image, video_frame))
+  const vpx_image_t* vpx_image_alpha = nullptr;
+  AlphaDecodeStatus alpha_decode_status =
+      DecodeAlphaPlane(vpx_image, &vpx_image_alpha, buffer);
+  if (alpha_decode_status == kFailure) {
     return false;
+  } else if (alpha_decode_status == kNoAlphaPlaneData) {
+    *video_frame = nullptr;
+    return true;
+  }
+  if (!CopyVpxImageToVideoFrame(vpx_image, vpx_image_alpha, video_frame)) {
+    return false;
+  }
+  if (vpx_image_alpha && config_.codec() == kCodecVP8) {
+    libyuv::CopyPlane(vpx_image_alpha->planes[VPX_PLANE_Y],
+                      vpx_image_alpha->stride[VPX_PLANE_Y],
+                      (*video_frame)->visible_data(VideoFrame::kAPlane),
+                      (*video_frame)->stride(VideoFrame::kAPlane),
+                      (*video_frame)->visible_rect().width(),
+                      (*video_frame)->visible_rect().height());
+  }
 
   (*video_frame)->set_timestamp(base::TimeDelta::FromMicroseconds(timestamp));
 
@@ -485,82 +505,84 @@ bool VpxVideoDecoder::VpxDecode(const scoped_refptr<DecoderBuffer>& buffer,
   (*video_frame)
       ->metadata()
       ->SetInteger(VideoFrameMetadata::COLOR_SPACE, color_space);
+  return true;
+}
 
-  if (!vpx_codec_alpha_)
-    return true;
-
-  if (buffer->side_data_size() < 8) {
-    // TODO(mcasas): Is this a warning or an error?
-    DLOG(WARNING) << "Making Alpha channel opaque due to missing input";
-    const uint32_t kAlphaOpaqueValue = 255;
-    libyuv::SetPlane((*video_frame)->visible_data(VideoFrame::kAPlane),
-                     (*video_frame)->stride(VideoFrame::kAPlane),
-                     (*video_frame)->visible_rect().width(),
-                     (*video_frame)->visible_rect().height(),
-                     kAlphaOpaqueValue);
-    return true;
-  }
-
-  // First 8 bytes of side data is |side_data_id| in big endian.
-  const uint64_t side_data_id = base::NetToHost64(
-      *(reinterpret_cast<const uint64_t*>(buffer->side_data())));
-  if (side_data_id != 1)
-    return true;
-
-  // Try and decode buffer->side_data() minus the first 8 bytes as a full frame.
-  int64_t timestamp_alpha = buffer->timestamp().InMicroseconds();
-  void* user_priv_alpha = reinterpret_cast<void*>(&timestamp_alpha);
-  {
-    TRACE_EVENT1("video", "vpx_codec_decode_alpha", "timestamp_alpha",
-                 timestamp_alpha);
-    vpx_codec_err_t status = vpx_codec_decode(
-        vpx_codec_alpha_, buffer->side_data() + 8, buffer->side_data_size() - 8,
-        user_priv_alpha, 0 /* deadline */);
-    if (status != VPX_CODEC_OK) {
-      DLOG(ERROR) << "vpx_codec_decode() failed for the alpha: "
-                  << vpx_codec_error(vpx_codec_);
-      return false;
+AlphaDecodeStatus VpxVideoDecoder::DecodeAlphaPlane(
+    const struct vpx_image* vpx_image,
+    const struct vpx_image** vpx_image_alpha,

[DaleCurtis, 2016/01/13 01:32:28]

possible to avoid passing **?

[vignesh, 2016/01/13 04:01:10]

i can swap this with the return value. that would mean passing a
AlphaDecodeStatus*, would that be ok?

[DaleCurtis, 2016/01/13 18:59:55]

It's no different semantically, so what you have is fine.

+    const scoped_refptr<DecoderBuffer>& buffer,
+    scoped_refptr<VideoFrame>* video_frame) {
+  if (vpx_codec_alpha_ && buffer->side_data_size() >= 8) {

[DaleCurtis, 2016/01/13 01:32:28]

return early instead of indenting the whole function, ditto for a few of the
conditionals below too.

[vignesh, 2016/01/15 18:07:13]

Done.

+    // First 8 bytes of side data is |side_data_id| in big endian.
+    const uint64_t side_data_id = base::NetToHost64(
+        *(reinterpret_cast<const uint64_t*>(buffer->side_data())));
+    if (side_data_id == 1) {
+      // Try and decode buffer->side_data() minus the first 8 bytes as a full
+      // frame.
+      int64_t timestamp_alpha = buffer->timestamp().InMicroseconds();
+      void* user_priv_alpha = reinterpret_cast<void*>(&timestamp_alpha);
+      {
+        TRACE_EVENT1("video", "vpx_codec_decode_alpha", "timestamp_alpha",
+                     timestamp_alpha);
+        vpx_codec_err_t status = vpx_codec_decode(
+            vpx_codec_alpha_, buffer->side_data() + 8,
+            buffer->side_data_size() - 8, user_priv_alpha, 0 /* deadline */);
+        if (status != VPX_CODEC_OK) {
+          DLOG(ERROR) << "vpx_codec_decode() failed for the alpha: "
+                      << vpx_codec_error(vpx_codec_);
+          return kError;
+        }
+      }
+
+      vpx_codec_iter_t iter_alpha = NULL;
+      *vpx_image_alpha = vpx_codec_get_frame(vpx_codec_alpha_, &iter_alpha);
+      if (!(*vpx_image_alpha)) {
+        return kNoAlphaPlaneData;

[DaleCurtis, 2016/01/13 01:32:28]

It's a bit confusing that kOk is returned for non-alpha video. Not sure of a
better suggestion though.

[vignesh, 2016/01/13 04:01:10]

I defined the function semantic as follows:
* returns kOk if there are no fatal errors. In this case vpx_image_alpha will be
populated if a valid alpha plane exists, otherwise it will be null.
* return kFailure on a fatal error. in this case vpx_image_alpha will be null.
* return kNoAlphaPlane if a non-fatal error occurred. vpx_image_alpha will be
null.

Thoughts on changing this for better?

[DaleCurtis, 2016/01/13 18:59:55]

Nope, if nothing sticks out lets just go with this.

+      }
+
+      if ((*vpx_image_alpha)->user_priv != user_priv_alpha) {
+        DLOG(ERROR) << "Invalid output timestamp on alpha.";
+        return kError;
+      }
+
+      if ((*vpx_image_alpha)->d_h != vpx_image->d_h ||
+          (*vpx_image_alpha)->d_w != vpx_image->d_w) {
+        DLOG(ERROR) << "The alpha plane dimensions are not the same as the "
+                       "image dimensions.";
+        return kError;
+      }
+
+      if (config_.codec() == kCodecVP9) {
+        VpxVideoDecoder::MemoryPool::VP9FrameBuffer* frame_buffer =
+            static_cast<VpxVideoDecoder::MemoryPool::VP9FrameBuffer*>(
+                vpx_image->fb_priv);
+        uint64_t alpha_plane_size =
+            (*vpx_image_alpha)->stride[VPX_PLANE_Y] * (*vpx_image_alpha)->d_h;
+        if (frame_buffer->alpha_data.size() < alpha_plane_size) {
+          frame_buffer->alpha_data.resize(alpha_plane_size);
+        }
+        libyuv::CopyPlane((*vpx_image_alpha)->planes[VPX_PLANE_Y],
+                          (*vpx_image_alpha)->stride[VPX_PLANE_Y],
+                          &frame_buffer->alpha_data[0],
+                          (*vpx_image_alpha)->stride[VPX_PLANE_Y],
+                          (*vpx_image_alpha)->d_w, (*vpx_image_alpha)->d_h);
+      }
     }
   }
-
-  vpx_codec_iter_t iter_alpha = NULL;
-  const vpx_image_t* vpx_image_alpha =
-      vpx_codec_get_frame(vpx_codec_alpha_, &iter_alpha);
-  if (!vpx_image_alpha) {
-    *video_frame = nullptr;
-    return true;
-  }
-
-  if (vpx_image_alpha->user_priv != user_priv_alpha) {
-    DLOG(ERROR) << "Invalid output timestamp on alpha.";
-    return false;
-  }
-
-  if (vpx_image_alpha->d_h != vpx_image->d_h ||
-      vpx_image_alpha->d_w != vpx_image->d_w) {
-    DLOG(ERROR) << "The alpha plane dimensions are not the same as the "
-                   "image dimensions.";
-    return false;
-  }
-
-  libyuv::CopyPlane(vpx_image_alpha->planes[VPX_PLANE_Y],
-                    vpx_image_alpha->stride[VPX_PLANE_Y],
-                    (*video_frame)->visible_data(VideoFrame::kAPlane),
-                    (*video_frame)->stride(VideoFrame::kAPlane),
-                    (*video_frame)->visible_rect().width(),
-                    (*video_frame)->visible_rect().height());
-  return true;
+  return kOk;
 }
 
 bool VpxVideoDecoder::CopyVpxImageToVideoFrame(
     const struct vpx_image* vpx_image,
+    const struct vpx_image* vpx_image_alpha,
     scoped_refptr<VideoFrame>* video_frame) {
   DCHECK(vpx_image);
 
   VideoPixelFormat codec_format;
   switch (vpx_image->fmt) {
     case VPX_IMG_FMT_I420:
-      codec_format = vpx_codec_alpha_ ? PIXEL_FORMAT_YV12A : PIXEL_FORMAT_YV12;
+      codec_format = vpx_image_alpha ? PIXEL_FORMAT_YV12A : PIXEL_FORMAT_YV12;
       break;
 
     case VPX_IMG_FMT_I444:
@@ -581,17 +603,25 @@ bool VpxVideoDecoder::CopyVpxImageToVideoFrame(
 
   if (memory_pool_.get()) {
     DCHECK_EQ(kCodecVP9, config_.codec());
-    DCHECK(!vpx_codec_alpha_) << "Uh-oh, VP9 and Alpha shouldn't coexist.";
-    *video_frame = VideoFrame::WrapExternalYuvData(
-        codec_format,
-        coded_size, gfx::Rect(visible_size), config_.natural_size(),
-        vpx_image->stride[VPX_PLANE_Y],
-        vpx_image->stride[VPX_PLANE_U],
-        vpx_image->stride[VPX_PLANE_V],
-        vpx_image->planes[VPX_PLANE_Y],
-        vpx_image->planes[VPX_PLANE_U],
-        vpx_image->planes[VPX_PLANE_V],
-        kNoTimestamp());
+    if (vpx_image_alpha) {
+      VpxVideoDecoder::MemoryPool::VP9FrameBuffer* frame_buffer =
+          static_cast<VpxVideoDecoder::MemoryPool::VP9FrameBuffer*>(
+              vpx_image->fb_priv);
+      *video_frame = VideoFrame::WrapExternalYuvaData(
+          codec_format, coded_size, gfx::Rect(visible_size),
+          config_.natural_size(), vpx_image->stride[VPX_PLANE_Y],
+          vpx_image->stride[VPX_PLANE_U], vpx_image->stride[VPX_PLANE_V],
+          vpx_image_alpha->stride[VPX_PLANE_Y], vpx_image->planes[VPX_PLANE_Y],
+          vpx_image->planes[VPX_PLANE_U], vpx_image->planes[VPX_PLANE_V],
+          &frame_buffer->alpha_data[0], kNoTimestamp());
+    } else {
+      *video_frame = VideoFrame::WrapExternalYuvData(
+          codec_format, coded_size, gfx::Rect(visible_size),
+          config_.natural_size(), vpx_image->stride[VPX_PLANE_Y],
+          vpx_image->stride[VPX_PLANE_U], vpx_image->stride[VPX_PLANE_V],
+          vpx_image->planes[VPX_PLANE_Y], vpx_image->planes[VPX_PLANE_U],
+          vpx_image->planes[VPX_PLANE_V], kNoTimestamp());
+    }
     video_frame->get()->AddDestructionObserver(
         memory_pool_->CreateFrameCallback(vpx_image->fb_priv));