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diff --git a/third_party/libwebrtc/modules/video_coding/codecs/multiplex/multiplex_encoded_image_packer.h b/third_party/libwebrtc/modules/video_coding/codecs/multiplex/multiplex_encoded_image_packer.h
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+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef MODULES_VIDEO_CODING_CODECS_MULTIPLEX_MULTIPLEX_ENCODED_IMAGE_PACKER_H_
+#define MODULES_VIDEO_CODING_CODECS_MULTIPLEX_MULTIPLEX_ENCODED_IMAGE_PACKER_H_
+
+#include <cstdint>
+#include <memory>
+#include <vector>
+
+#include "api/video/encoded_image.h"
+#include "api/video_codecs/video_codec.h"
+
+namespace webrtc {
+
+// Struct describing the whole bundle of multiple frames of an image.
+// This struct is expected to be the set in the beginning of a picture's
+// bitstream data.
+struct MultiplexImageHeader {
+  // The number of frame components making up the complete picture data.
+  // For example, `frame_count` = 2 for the case of YUV frame with Alpha frame.
+  uint8_t component_count;
+
+  // The increasing image ID given by the encoder. For different components
+  // of a single picture, they have the same `picture_index`.
+  uint16_t image_index;
+
+  // The location of the first MultiplexImageComponentHeader in the bitstream,
+  // in terms of byte from the beginning of the bitstream.
+  uint32_t first_component_header_offset;
+
+  // The location of the augmenting data in the bitstream, in terms of bytes
+  // from the beginning of the bitstream
+  uint32_t augmenting_data_offset;
+
+  // The size of the augmenting data in the bitstream it terms of byte
+  uint16_t augmenting_data_size;
+};
+const int kMultiplexImageHeaderSize =
+    sizeof(uint8_t) + 2 * sizeof(uint16_t) + 2 * sizeof(uint32_t);
+
+// Struct describing the individual image component's content.
+struct MultiplexImageComponentHeader {
+  // The location of the next MultiplexImageComponentHeader in the bitstream,
+  // in terms of the byte from the beginning of the bitstream;
+  uint32_t next_component_header_offset;
+
+  // Identifies which component this frame represent, i.e. YUV frame vs Alpha
+  // frame.
+  uint8_t component_index;
+
+  // The location of the real encoded image data of the frame in the bitstream,
+  // in terms of byte from the beginning of the bitstream.
+  uint32_t bitstream_offset;
+
+  // Indicates the number of bytes of the encoded image data.
+  uint32_t bitstream_length;
+
+  // Indicated the underlying VideoCodecType of the frame, i.e. VP9 or VP8 etc.
+  VideoCodecType codec_type;
+
+  // Indicated the underlying frame is a key frame or delta frame.
+  VideoFrameType frame_type;
+};
+const int kMultiplexImageComponentHeaderSize =
+    sizeof(uint32_t) + sizeof(uint8_t) + sizeof(uint32_t) + sizeof(uint32_t) +
+    sizeof(uint8_t) + sizeof(uint8_t);
+
+// Struct holding the encoded image for one component.
+struct MultiplexImageComponent {
+  // Indicated the underlying VideoCodecType of the frame, i.e. VP9 or VP8 etc.
+  VideoCodecType codec_type;
+
+  // Identifies which component this frame represent, i.e. YUV frame vs Alpha
+  // frame.
+  uint8_t component_index;
+
+  // Stores the actual frame data of the encoded image.
+  EncodedImage encoded_image;
+};
+
+// Struct holding the whole frame bundle of components of an image.
+struct MultiplexImage {
+  uint16_t image_index;
+  uint8_t component_count;
+  uint16_t augmenting_data_size;
+  std::unique_ptr<uint8_t[]> augmenting_data;
+  std::vector<MultiplexImageComponent> image_components;
+
+  MultiplexImage(uint16_t picture_index,
+                 uint8_t component_count,
+                 std::unique_ptr<uint8_t[]> augmenting_data,
+                 uint16_t augmenting_data_size);
+};
+
+// A utility class providing conversion between two representations of a
+// multiplex image frame:
+// 1. Packed version is just one encoded image, we pack all necessary metadata
+//    in the bitstream as headers.
+// 2. Unpacked version is essentially a list of encoded images, one for one
+//    component.
+class MultiplexEncodedImagePacker {
+ public:
+  // Note: It is caller responsibility to release the buffer of the result.
+  static EncodedImage PackAndRelease(const MultiplexImage& image);
+
+  // Note: The image components just share the memory with `combined_image`.
+  static MultiplexImage Unpack(const EncodedImage& combined_image);
+};
+
+}  // namespace webrtc
+
+#endif  // MODULES_VIDEO_CODING_CODECS_MULTIPLEX_MULTIPLEX_ENCODED_IMAGE_PACKER_H_