Add FFmpeg audio decoder for the clear key CDM.

webkit/media/crypto/ppapi/ffmpeg_cdm_audio_decoder.h

+// Copyright (c) 2012 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 WEBKIT_MEDIA_CRYPTO_PPAPI_FFMPEG_CDM_AUDIO_DECODER_H_
+#define WEBKIT_MEDIA_CRYPTO_PPAPI_FFMPEG_CDM_AUDIO_DECODER_H_
+
+#include <vector>
+
+#include "base/basictypes.h"
+#include "base/time.h"
+#include "base/compiler_specific.h"
+#include "webkit/media/crypto/ppapi/content_decryption_module.h"
+
+struct AVCodecContext;
+struct AVFrame;
+
+namespace webkit_media {
+
+class FFmpegCdmAudioDecoder {
+ public:
+  explicit FFmpegCdmAudioDecoder(cdm::Allocator* allocator);
+  ~FFmpegCdmAudioDecoder();
+  bool Initialize(const cdm::AudioDecoderConfig& config);
+  void Deinitialize();
+  void Reset();
+
+  // Returns true when |config| is a valid audio decoder configuration.
+  static bool IsValidConfig(const cdm::AudioDecoderConfig& config);
+
+  // Decodes |compressed_buffer|. Stores output frame in |decoded_frames| and
+  // returns |cdm::kSuccess| when an output is available. Returns
+  // |cdm::kNeedMoreData| when |compressed_frame| does not produce a output.
+  // Returns |cdm::kDecodeError| when decoding fails.

[xhwang, 2012/10/24 08:18:15]

// Decodes |compressed_buffer|.
// Returns |cdm::kSuccess| and stores output frame in |decoded_frames| when an
output is available.
// Returns |cdm::kNeedMoreData| when |compressed_frame| does not produce a*n*
output.
// Returns |cdm::kDecodeError| when decoding fails.

[Tom Finegan, 2012/10/24 21:16:44]

I didn't use your wording, but your main concern seems to be that the first
thing the second second says is "Returns X". That's addressed, assuming you
agree with the new comment. :)

[xhwang, 2012/10/24 22:24:19]

ok

+  cdm::Status DecodeBuffer(const uint8_t* compressed_buffer,
+                           int32_t compressed_buffer_size,
+                           int64_t timestamp,
+                           cdm::AudioFrames* decoded_frames);
+
+ private:
+  void ResetOutputTime();
+  void ReleaseFFmpegResources();
+
+  base::TimeDelta GetNextOutputTimestamp() const;
+
+  void SerializeInt64(int64_t value);
+
+  // FFmpeg structures owned by this object.
+  AVCodecContext* codec_context_;
+  AVFrame* av_frame_;
+
+  bool is_initialized_;
+
+  cdm::Allocator* const allocator_;

[xhwang, 2012/10/24 08:18:15]

Declaration order doesn't match initialization order. Can we move allocator
and is_initialized up?

[Tom Finegan, 2012/10/24 21:16:44]

Done.

+
+  // Decoded audio format.
+  int bits_per_channel_;
+  int samples_per_second_;
+
+  // Used for computing output timestamps.
+  int bytes_per_frame_;
+  base::TimeDelta output_timestamp_base_;
+  double total_frames_decoded_;

[xhwang, 2012/10/24 08:18:15]

I know this is from media code, but it seems to me this number is always an
integer. How about use an int? When we do division, we can always cast to double
to preserve precision if needed.

[Tom Finegan, 2012/10/24 21:16:44]

Done.

+  base::TimeDelta last_input_timestamp_;
+
+  // Number of output sample bytes to drop before generating
+  // output buffers.
+  int output_bytes_to_drop_;
+
+  typedef std::vector<uint8_t> SerializedAudioFrames;
+  SerializedAudioFrames serialized_audio_frames_;
+
+  DISALLOW_COPY_AND_ASSIGN(FFmpegCdmAudioDecoder);
+};
+
+}  // namespace webkit_media
+
+#endif  // WEBKIT_MEDIA_CRYPTO_PPAPI_FFMPEG_CDM_AUDIO_DECODER_H_