Add offset support to BitstreamBuffer.

media/base/bitstream_buffer.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef MEDIA_BASE_BITSTREAM_BUFFER_H_
 #define MEDIA_BASE_BITSTREAM_BUFFER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
 #include "base/macros.h"
 #include "base/memory/shared_memory.h"
 #include "base/time/time.h"
 #include "ipc/ipc_param_traits.h"
 #include "media/base/decrypt_config.h"
 #include "media/base/media_export.h"
 #include "media/base/timestamp_constants.h"
 
 namespace media {
 
 // Class for passing bitstream buffers around.  Does not take ownership of the
 // data.  This is the media-namespace equivalent of PP_VideoBitstreamBuffer_Dev.
 class MEDIA_EXPORT BitstreamBuffer {
  public:
   BitstreamBuffer();
 
-  BitstreamBuffer(int32_t id, base::SharedMemoryHandle handle, size_t size);
-
+  // Constructs a new BitstreamBuffer. The content of the bitstream is located
+  // at |offset| bytes away from the start of the shared memory and the payload
+  // is |size| bytes. When not provided, the default value for |offset| is 0.
+  // |presentation_timestamp| is when the decoded frame should be displayed.
+  // When not provided, |presentation_timestamp| will be
+  // |media::kNoTimestamp()|.
   BitstreamBuffer(int32_t id,
                   base::SharedMemoryHandle handle,
                   size_t size,
-                  base::TimeDelta presentation_timestamp);
+                  off_t offset = 0,
+                  base::TimeDelta presentation_timestamp = kNoTimestamp());
 
   ~BitstreamBuffer();
 
   void SetDecryptConfig(const DecryptConfig& decrypt_config);
 
   int32_t id() const { return id_; }
   base::SharedMemoryHandle handle() const { return handle_; }
+
+  // The number of bytes of the actual bitstream data. It is the size of the
+  // content instead of the whole shared memory.
   size_t size() const { return size_; }
 
-  void set_handle(const base::SharedMemoryHandle& handle) { handle_ = handle; }
+  // The offset to the start of actual bitstream data in the shared memory.
+  off_t offset() const { return offset_; }
 
   // The timestamp is only valid if it's not equal to |media::kNoTimestamp()|.
   base::TimeDelta presentation_timestamp() const {
     return presentation_timestamp_;
   }
 
+  void set_handle(const base::SharedMemoryHandle& handle) { handle_ = handle; }
+
   // The following methods come from DecryptConfig.
 
   const std::string& key_id() const { return key_id_; }
   const std::string& iv() const { return iv_; }
   const std::vector<SubsampleEntry>& subsamples() const { return subsamples_; }
 
  private:
   int32_t id_;
   base::SharedMemoryHandle handle_;
   size_t size_;
+  off_t offset_;
 
   // This is only set when necessary. For example, AndroidVideoDecodeAccelerator
   // needs the timestamp because the underlying decoder may require it to
   // determine the output order.
   base::TimeDelta presentation_timestamp_;
 
   // The following fields come from DecryptConfig.
   // TODO(timav): Try to DISALLOW_COPY_AND_ASSIGN and include these params as
   // scoped_ptr<DecryptConfig> or explain why copy & assign is needed.
 
   std::string key_id_;                      // key ID.
   std::string iv_;                          // initialization vector
   std::vector<SubsampleEntry> subsamples_;  // clear/cypher sizes
 
   friend struct IPC::ParamTraits<media::BitstreamBuffer>;
 
   // Allow compiler-generated copy & assign constructors.
 };
 
 }  // namespace media
 
 #endif  // MEDIA_BASE_BITSTREAM_BUFFER_H_