[Chromecast] Change DecryptContext Decrypt API

chromecast/public/media/decrypt_context.h

 // Copyright 2015 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 CHROMECAST_PUBLIC_MEDIA_DECRYPT_CONTEXT_H_
 #define CHROMECAST_PUBLIC_MEDIA_DECRYPT_CONTEXT_H_
 
 #include <stdint.h>
 #include <vector>
 
 #include "cast_key_system.h"
 
 namespace chromecast {
 namespace media {
 class CastDecoderBuffer;
 
 // Provides the information needed to decrypt frames.
 class DecryptContext {
  public:
   virtual ~DecryptContext() {}
 
   // Get the key system to use for decryption.
   virtual CastKeySystem GetKeySystem() = 0;
 
-  // Decrypts the given buffer.  Returns true/false for success/failure,
-  // and places the decrypted data in output if successful.
+  // Decrypts the given buffer. Returns true/false for success/failure.
+  //
+  // The decrypted data will be of size |buffer.data_size()| and there must be
+  // enough space in |output| to store that data.
+  //
+  // If non-zero, |data_offset| specifies an offset to be applied to |output|
+  // before the decrypted data is written.
   virtual bool Decrypt(CastDecoderBuffer* buffer,
-                       std::vector<uint8_t>* output) = 0;
+                       uint8_t* output,
+                       size_t data_offset) = 0;
 };
 
 }  // namespace media
 }  // namespace chromecast
 
 #endif  // CHROMECAST_PUBLIC_MEDIA_DECRYPT_CONTEXT_H_