MP4 support for Common Encryption 'cbcs' scheme.

media/formats/mp4/box_definitions.cc

Index: media/formats/mp4/box_definitions.cc
diff --git a/media/formats/mp4/box_definitions.cc b/media/formats/mp4/box_definitions.cc
index 82a94709f73f5572dd0f2dc6b52fe5c41080b9fb..c23eea94ddc2fa5f1b4706e17a5d5b2643c990ba 100644
--- a/media/formats/mp4/box_definitions.cc
+++ b/media/formats/mp4/box_definitions.cc
@@ -23,6 +23,12 @@
 namespace media {
 namespace mp4 {
 
+namespace {
+
+const size_t kKeyIdSize = 16;
+
+}  // namespace
+
 FileType::FileType() {}
 FileType::FileType(const FileType& other) = default;
 FileType::~FileType() {}
@@ -240,16 +246,27 @@ FourCC TrackEncryption::BoxType() const { return FOURCC_TENC; }
 
 bool TrackEncryption::Parse(BoxReader* reader) {
   uint8_t flag;
-  RCHECK(reader->ReadFullBoxHeader() &&
-         reader->SkipBytes(2) &&
-         reader->Read1(&flag) &&
-         reader->Read1(&default_iv_size) &&
-         reader->ReadVec(&default_kid, 16));
+  uint8_t possible_pattern_info;
+  RCHECK(reader->ReadFullBoxHeader() && reader->SkipBytes(1) &&
+         reader->Read1(&possible_pattern_info) && reader->Read1(&flag) &&
+         reader->Read1(&default_iv_size) && reader->ReadVec(&default_kid, 16));

[kqyang, 2016/05/23 20:57:34]

s/16/kKeyIdSize/

[dougsteed, 2016/05/25 17:23:21]

Done.

   is_encrypted = (flag != 0);
-  if (is_encrypted) {
+  if (default_iv_size != 0) {
     RCHECK(default_iv_size == 8 || default_iv_size == 16);
+#if BUILDFLAG(ENABLE_CENC_NEW_EDITIONS)

[kqyang, 2016/05/23 20:57:34]

I'd prefer as less preprocessor primitive in the code as possible. I think we
can rename the flag to ENABLE_CENC_PATTERN_ENCRYPTION and have it in
HasSupportedScheme() alone should be sufficient.

+ddorwin, do you have a preference / guideline or preprocessor conditions?

[ddorwin, 2016/05/24 23:25:03]

I'm worried about all the ifdef'd code being added, but I'm also wary of
including code in all builds that is not used by nearly all Chrome platforms.

Most importantly, though, I think this flag name is inaccurate. See my comments
in the .gni file.

[dougsteed, 2016/05/25 17:23:21]

Changed the name as suggested.

+  } else if (is_encrypted) {
+    if (reader->version() > 0) {
+      default_crypt_byte_block = (possible_pattern_info >> 4) & 0x0f;
+      default_skip_byte_block = possible_pattern_info & 0x0f;
+    }
+    RCHECK(reader->Read1(&default_constant_iv_size) &&
+           (default_constant_iv_size == 8 || default_constant_iv_size == 16));
+    memset(default_constant_iv, 0, sizeof(default_constant_iv));
+    for (uint8_t i = 0; i < default_constant_iv_size; i++)
+      RCHECK(reader->Read1(default_constant_iv + i));
+#endif
   } else {
-    RCHECK(default_iv_size == 0);
+    RCHECK(!is_encrypted);
   }
   return true;
 }
@@ -273,7 +290,7 @@ bool ProtectionSchemeInfo::Parse(BoxReader* reader) {
   RCHECK(reader->ScanChildren() &&
          reader->ReadChild(&format) &&
          reader->ReadChild(&type));
-  if (type.type == FOURCC_CENC)
+  if (HasSupportedScheme())
     RCHECK(reader->ReadChild(&info));
   // Other protection schemes are silently ignored. Since the protection scheme
   // type can't be determined until this box is opened, we return 'true' for
@@ -282,6 +299,18 @@ bool ProtectionSchemeInfo::Parse(BoxReader* reader) {
   return true;
 }
 
+bool ProtectionSchemeInfo::HasSupportedScheme() const {
+  FourCC fourCC = type.type;
+  if (fourCC == FOURCC_CENC)
+    return true;
+#if BUILDFLAG(ENABLE_CENC_NEW_EDITIONS)
+  return fourCC == FOURCC_CBC1 || fourCC == FOURCC_CBCS ||

[ddorwin, 2016/05/24 23:25:03]

Are there actual use cases for the other two? If not, I think we should avoid
advertising them unless there is a proven need.

[dougsteed, 2016/05/25 17:23:21]

Done.

+         fourCC == FOURCC_CENS;
+#else
+  return false;
+#endif
+}
+
 MovieHeader::MovieHeader()
     : creation_time(0),
       modification_time(0),
@@ -609,7 +638,7 @@ bool VideoSampleEntry::Parse(BoxReader* reader) {
   if (format == FOURCC_ENCV) {
     // Continue scanning until a recognized protection scheme is found, or until
     // we run out of protection schemes.
-    while (sinf.type.type != FOURCC_CENC) {
+    while (!sinf.HasSupportedScheme()) {
       if (!reader->ReadChild(&sinf))
         return false;
     }
@@ -749,7 +778,7 @@ bool AudioSampleEntry::Parse(BoxReader* reader) {
   if (format == FOURCC_ENCA) {
     // Continue scanning until a recognized protection scheme is found, or until
     // we run out of protection schemes.
-    while (sinf.type.type != FOURCC_CENC) {
+    while (!sinf.HasSupportedScheme()) {
       if (!reader->ReadChild(&sinf))
         return false;
     }
@@ -1094,6 +1123,32 @@ CencSampleEncryptionInfoEntry::CencSampleEncryptionInfoEntry(
     const CencSampleEncryptionInfoEntry& other) = default;
 CencSampleEncryptionInfoEntry::~CencSampleEncryptionInfoEntry() {}
 
+bool CencSampleEncryptionInfoEntry::Parse(BoxReader* reader) {
+  uint8_t flag;
+  uint8_t possible_pattern_info;
+  RCHECK(reader->SkipBytes(1) &&  // reserved.
+         reader->Read1(&possible_pattern_info) && reader->Read1(&flag) &&
+         reader->Read1(&iv_size) && reader->ReadVec(&key_id, kKeyIdSize));
+
+  is_encrypted = (flag != 0);
+  if (iv_size != 0) {
+    RCHECK(iv_size == 8 || iv_size == 16);
+#if BUILDFLAG(ENABLE_CENC_NEW_EDITIONS)
+  } else if (is_encrypted) {
+    crypt_byte_block = (possible_pattern_info >> 4) & 0x0f;
+    skip_byte_block = possible_pattern_info & 0x0f;
+    RCHECK(reader->Read1(&constant_iv_size) &&
+           (constant_iv_size == 8 || constant_iv_size == 16));
+    memset(constant_iv, 0, sizeof(constant_iv));
+    for (uint8_t i = 0; i < constant_iv_size; i++)
+      RCHECK(reader->Read1(constant_iv + i));
+#endif
+  } else {
+    RCHECK(!is_encrypted);
+  }
+  return true;
+}
+
 SampleGroupDescription::SampleGroupDescription() : grouping_type(0) {}
 SampleGroupDescription::SampleGroupDescription(
     const SampleGroupDescription& other) = default;
@@ -1112,7 +1167,6 @@ bool SampleGroupDescription::Parse(BoxReader* reader) {
 
   const uint8_t version = reader->version();
 
-  const size_t kKeyIdSize = 16;
   const size_t kEntrySize = sizeof(uint32_t) + kKeyIdSize;
   uint32_t default_length = 0;
   if (version == 1) {
@@ -1131,19 +1185,7 @@ bool SampleGroupDescription::Parse(BoxReader* reader) {
         RCHECK(description_length >= kEntrySize);
       }
     }
-
-    uint8_t flag;
-    RCHECK(reader->SkipBytes(2) &&  // reserved.
-           reader->Read1(&flag) &&
-           reader->Read1(&entries[i].iv_size) &&
-           reader->ReadVec(&entries[i].key_id, kKeyIdSize));
-
-    entries[i].is_encrypted = (flag != 0);
-    if (entries[i].is_encrypted) {
-      RCHECK(entries[i].iv_size == 8 || entries[i].iv_size == 16);
-    } else {
-      RCHECK(entries[i].iv_size == 0);
-    }
+    RCHECK(entries[i].Parse(reader));
   }
   return true;
 }