media config: expand is_encrypted to a struct.

media/base/encryption_scheme.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 MEDIA_BASE_ENCRYPTION_SCHEME_H_
+#define MEDIA_BASE_ENCRYPTION_SCHEME_H_
+
+#include <stdint.h>
+
+#include "media/base/media_export.h"
+
+namespace media {
+
+// Specification of whether and how the stream is encrypted (in whole or part).
+class MEDIA_EXPORT EncryptionScheme {
+ public:
+  // Algorithm and mode used for encryption. kCipherModeUnencrypted indicates
+  // no encryption.
+  enum CipherMode {
+    kCipherModeUnencrypted,
+    kCipherModeAesCtr,
+    kCipherModeAesCbc,
+    kCipherModeMax = kCipherModeAesCbc
+  };
+
+  // CENC 3rd Edition adds pattern encryption, through two new protection
+  // schemes: 'cens' (with AES-CTR) and 'cbcs' (with AES-CBC).
+  // The pattern applies independently to each 'encrypted' part of the frame (as
+  // defined by the relevant subsample entries), and reduces further the
+  // actual encryption applied through a repeating pattern of (encrypt:skip)
+  // 16 byte blocks. For example, in a (1:9) pattern, the first block is
+  // encrypted, and the next nine are skipped. This pattern is applied
+  // repeatedly until the end of the last 16-byte block in the subsample.
+  // Any remaining bytes are left clear.
+  // If either of encrypt_blocks or skip_blocks is 0, pattern encryption is
+  // disabled.
+  class Pattern {
+   public:
+    Pattern();
+    Pattern(uint32_t encrypt_blocks, uint32_t skip_blocks);
+    ~Pattern();
+
+    bool Matches(const Pattern& other) const;
+
+    uint32_t encrypt_blocks() const { return encrypt_blocks_; }
+    uint32_t skip_blocks() const { return skip_blocks_; }
+
+    bool IsInEffect() const;
+
+   private:
+    uint32_t encrypt_blocks_ = 0;
+    uint32_t skip_blocks_ = 0;
+
+    // Allow copy and assignment.
+  };
+
+  // The default constructor makes an instance that indicates no encryption.
+  EncryptionScheme();
+
+  // This constructor allows specification of the cipher mode with no pattern.

[ddorwin, 2016/03/04 20:24:36]

Now that we have the medi_util helpers, how much do we use this constructor? Can
we eliminate it now?

[dougsteed, 2016/03/07 17:49:13]

Done.

[xhwang, 2016/03/07 18:39:52]

This is not done yet...

[dougsteed, 2016/03/07 21:12:40]

Done.

+  explicit EncryptionScheme(CipherMode mode);
+
+  // This constructor allows specification of the cipher mode and the pattern.
+  EncryptionScheme(CipherMode mode, const Pattern& pattern);
+  ~EncryptionScheme();
+
+  bool Matches(const EncryptionScheme& other) const;
+
+  bool is_encrypted() const { return mode_ != kCipherModeUnencrypted; }
+  CipherMode mode() const { return mode_; }
+  const Pattern& pattern() const { return pattern_; }
+
+ private:
+  CipherMode mode_ = kCipherModeUnencrypted;
+  Pattern pattern_;
+
+  // Allow copy and assignment.
+};
+
+}  // namespace media
+
+#endif  // MEDIA_BASE_ENCRYPTION_SCHEME_H_