media config: expand is_encrypted to a struct.

chromecast/public/media/decoder_config.h

Index: chromecast/public/media/decoder_config.h
diff --git a/chromecast/public/media/decoder_config.h b/chromecast/public/media/decoder_config.h
index e2cf78dcbc6118608f4295c31ae9ff9e939c23ab..a8cc65fbbc98af326c4b489613e0499a1a9e4f4e 100644
--- a/chromecast/public/media/decoder_config.h
+++ b/chromecast/public/media/decoder_config.h
@@ -87,7 +87,82 @@ enum VideoProfile {
   kVideoProfileMax = kVP9ProfileAny,
 };
 
-// TODO(erickung): Remove constructor once CMA backend implementation does't
+// Algorithm and mode that was used to encrypt the stream.

[ddorwin, 2015/12/10 18:36:00]

Similar comments as in encryption_scheme.h.

[dougsteed, 2015/12/14 21:19:01]

Done.

+enum CipherMode {
+  kCipherModeUnknown,
+  kCipherModeAesCtr,
+  kCipherModeAesCbc
+};
+
+// Specification of whether and how the stream is encrypted (in whole or part).
+struct EncryptionScheme {
+  // V3 of the CENC standard will add pattern encryption, through two new
+  // protection schemes 'cens' (with AES-CTR) and 'cbcs' (with AES-CBC).
+  // The pattern applies only to the '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 or both of encrypt_blocks or skip_blocks is 0, pattern
+  // encryption is disabled.
+  struct PatternSpec {
+    PatternSpec();
+    PatternSpec(uint32_t encrypt_blocks, uint32_t skip_blocks);
+    ~PatternSpec() {}
+    uint32_t encrypt_blocks;
+    uint32_t skip_blocks;
+  };
+
+  EncryptionScheme();
+  EncryptionScheme(bool is_encrypted);
+  EncryptionScheme(CipherMode mode);
+  EncryptionScheme(CipherMode mode, const PatternSpec& pattern);
+  EncryptionScheme(bool is_encrypted, CipherMode, const PatternSpec& pattern);
+  ~EncryptionScheme() {}
+  bool is_encrypted;

[ddorwin, 2015/12/10 18:36:00]

Public members make things more interesting (and dangerous?) than in
encryption_scheme.h. Do these need to be public?

[dougsteed, 2015/12/14 21:19:01]

This is the house style for the chromecast media API objects, which are defined
by structs rather than classes (see the other examples that I didn't touch later
in this file. Not sure of the history of that, but not practical to change at
this point, as they are used in all the vendor APIs. 

+  CipherMode mode;
+  PatternSpec pattern;
+};
+
+inline EncryptionScheme::PatternSpec::PatternSpec()

[ddorwin, 2015/12/10 18:36:00]

Why are constructors and destructors inlined here? They are not supposed to be
per https://www.chromium.org/developers/coding-style#TOC-Inline-functions.

[dougsteed, 2015/12/14 21:19:01]

I'm following the existing style for the chromecast config structs (see later in
this file). And in fact, there actually IS no cc file for this! Again, I don't
know the history, but perhaps it is so the OEMs can use the corresponding APIs
in their libraries without having to link in separate cc files from us. And I
think this is OK under the guidelines, since there are no complex constructors,
they just assign PODs. 

+    : encrypt_blocks(0), skip_blocks(0) {
+}
+
+inline EncryptionScheme::PatternSpec::PatternSpec(uint32_t encrypt_blocks,
+                                                  uint32_t skip_blocks)
+    : encrypt_blocks(encrypt_blocks), skip_blocks(skip_blocks) {
+}
+
+inline EncryptionScheme::EncryptionScheme()
+    : is_encrypted(false), mode(kCipherModeUnknown), pattern() {
+}
+
+inline EncryptionScheme::EncryptionScheme(bool is_encrypted)
+    : is_encrypted(is_encrypted),
+      mode(is_encrypted ? kCipherModeAesCtr : kCipherModeUnknown),
+      pattern() {
+}
+
+inline EncryptionScheme::EncryptionScheme(CipherMode mode)
+    : is_encrypted(true), mode(mode), pattern() {
+}
+
+inline EncryptionScheme::EncryptionScheme(CipherMode mode,
+                                          const PatternSpec& pattern)
+    : is_encrypted(true), mode(mode), pattern(pattern) {
+}
+
+inline EncryptionScheme::EncryptionScheme(
+    bool is_encrypted,
+    CipherMode mode,
+    const PatternSpec& pattern)
+    :  is_encrypted(is_encrypted), mode(mode), pattern(pattern) {
+}
+
+
+// TODO(erickung): Remove constructor once CMA backend implementation doesn't
 // create a new object to reset the configuration and use IsValidConfig() to
 // determine if the configuration is still valid or not.
 struct AudioConfig {
@@ -108,8 +183,8 @@ struct AudioConfig {
   int samples_per_second;
   // Extra data buffer for certain codec initialization.
   std::vector<uint8_t> extra_data;
-  // content is encrypted or not.
-  bool is_encrypted;
+  // Encryption scheme (if any) used for the content.
+  EncryptionScheme encryption_scheme;
 };
 
 inline AudioConfig::AudioConfig()
@@ -119,7 +194,7 @@ inline AudioConfig::AudioConfig()
       bytes_per_channel(0),
       channel_number(0),
       samples_per_second(0),
-      is_encrypted(false) {
+      encryption_scheme(false) {
 }
 
 inline AudioConfig::~AudioConfig() {
@@ -144,8 +219,8 @@ struct VideoConfig {
   VideoConfig* additional_config;
   // Extra data buffer for certain codec initialization.
   std::vector<uint8_t> extra_data;
-  // content is encrypted or not.
-  bool is_encrypted;
+  // Encryption scheme (if any) used for the content.
+  EncryptionScheme encryption_scheme;
 };
 
 inline VideoConfig::VideoConfig()
@@ -153,7 +228,7 @@ inline VideoConfig::VideoConfig()
       codec(kVideoCodecUnknown),
       profile(kVideoProfileUnknown),
       additional_config(nullptr),
-      is_encrypted(false) {
+      encryption_scheme(false) {
 }
 
 inline VideoConfig::~VideoConfig() {