MP4 support for Common Encryption 'cbcs' scheme.

media/formats/mp4/track_run_iterator.cc

 // Copyright 2014 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.
 
 #include "media/formats/mp4/track_run_iterator.h"
 
 #include <algorithm>
 #include <iomanip>
 #include <limits>
 #include <memory>
 
 #include "base/macros.h"
 #include "media/formats/mp4/rcheck.h"
 #include "media/formats/mp4/sample_to_group_iterator.h"
+#include "media/media_features.h"
 
 namespace media {
 namespace mp4 {
 
 struct SampleInfo {
   int size;
   int duration;
   int cts_offset;
   bool is_keyframe;
   uint32_t cenc_group_description_index;
@@ skipping 291 matching lines @@
       TrackRunInfo tri;
       tri.track_id = traf.header.track_id;
       tri.timescale = trak->media.header.timescale;
       tri.start_dts = run_start_dts;
       tri.sample_start_offset = trun.data_offset;
       tri.track_sample_encryption_group =
           &trak->media.information.sample_table.sample_group_description;
       tri.fragment_sample_encryption_info =
           traf.sample_group_description.entries;
 
-      uint8_t default_iv_size = 0;
+      const TrackEncryption* track_encryption;
       tri.is_audio = (stsd.type == kAudio);
       if (tri.is_audio) {
         RCHECK(!stsd.audio_entries.empty());
         if (desc_idx > stsd.audio_entries.size())
           desc_idx = 0;
         tri.audio_description = &stsd.audio_entries[desc_idx];
-        default_iv_size =
-            tri.audio_description->sinf.info.track_encryption.default_iv_size;
+        track_encryption = &tri.audio_description->sinf.info.track_encryption;
       } else {
         RCHECK(!stsd.video_entries.empty());
         if (desc_idx > stsd.video_entries.size())
           desc_idx = 0;
         tri.video_description = &stsd.video_entries[desc_idx];
-        default_iv_size =
-            tri.video_description->sinf.info.track_encryption.default_iv_size;
+        track_encryption = &tri.video_description->sinf.info.track_encryption;
       }
-
       // Initialize aux_info variables only if no sample encryption entries.
       if (sample_encryption_entries_count == 0 &&
           traf.auxiliary_offset.offsets.size() > j) {
         // Collect information from the auxiliary_offset entry with the same
         // index in the 'saiz' container as the current run's index in the
         // 'trun' container, if it is present.
         // There should be an auxiliary info entry corresponding to each sample
         // in the auxiliary offset entry's corresponding track run.
         RCHECK(traf.auxiliary_size.sample_count >=
                sample_count_sum + trun.sample_count);
@@ skipping 47 matching lines @@
         if (index != 0)
           RCHECK(GetSampleEncryptionInfoEntry(tri, index));
         is_sample_to_group_valid = sample_to_group_itr.Advance();
       }
       if (sample_encryption_entries_count > 0) {
         RCHECK(sample_encryption_entries_count >=
                sample_count_sum + trun.sample_count);
         tri.sample_encryption_entries.resize(trun.sample_count);
         for (size_t k = 0; k < trun.sample_count; k++) {
           uint32_t index = tri.samples[k].cenc_group_description_index;
-          const uint8_t iv_size =
-              index == 0 ? default_iv_size
-                         : GetSampleEncryptionInfoEntry(tri, index)->iv_size;
-          RCHECK(tri.sample_encryption_entries[k].Parse(
-              sample_encryption_reader.get(), iv_size,
-              traf.sample_encryption.use_subsample_encryption));
+          const CencSampleEncryptionInfoEntry* info_entry =
+              index == 0 ? nullptr : GetSampleEncryptionInfoEntry(tri, index);
+          const uint8_t iv_size = index == 0 ? track_encryption->default_iv_size
+                                             : info_entry->iv_size;
+          SampleEncryptionEntry& entry = tri.sample_encryption_entries[k];
+          RCHECK(entry.Parse(sample_encryption_reader.get(), iv_size,
+                             traf.sample_encryption.use_subsample_encryption));
+#if BUILDFLAG(ENABLE_CBCS_ENCRYPTION_SCHEME)
+          // If we don't have a per-sample IV, get the constant IV.
+          bool is_encrypted = index == 0 ? track_encryption->is_encrypted
+                                         : info_entry->is_encrypted;
+          // We only support setting the pattern values in the 'tenc' box for
+          // the track (not varying on per sample group basis).
+          // Thus we need to verify that the settings in the sample group match
+          // those in the 'tenc'.
+          if (is_encrypted && index != 0) {
+            RCHECK(info_entry->crypt_byte_block ==
+                   track_encryption->default_crypt_byte_block);
+            RCHECK(info_entry->skip_byte_block ==
+                   track_encryption->default_skip_byte_block);
+          }
+          if (is_encrypted && !iv_size) {
+            const uint8_t constant_iv_size =
+                index == 0 ? track_encryption->default_constant_iv_size
+                           : info_entry->constant_iv_size;
+            RCHECK(constant_iv_size != 0);
+            const uint8_t* constant_iv =
+                index == 0 ? track_encryption->default_constant_iv
+                           : info_entry->constant_iv;
+            memcpy(entry.initialization_vector, constant_iv, constant_iv_size);
+          }
+#endif
         }
       }
       runs_.push_back(tri);
       sample_count_sum += trun.sample_count;
     }
 
     // We should have iterated through all samples in SampleToGroup Box.
     RCHECK(!sample_to_group_itr.IsValid());
   }
 
@@ skipping 40 matching lines @@
   int64_t pos = 0;
   for (size_t i = 0; i < run_itr_->samples.size(); i++) {
     int info_size = run_itr_->aux_info_default_size;
     if (!info_size)
       info_size = run_itr_->aux_info_sizes[i];
 
     if (IsSampleEncrypted(i)) {
       BufferReader reader(buf + pos, info_size);
       const uint8_t iv_size = GetIvSize(i);
       const bool has_subsamples = info_size > iv_size;
-      RCHECK(
-          sample_encryption_entries[i].Parse(&reader, iv_size, has_subsamples));
+      SampleEncryptionEntry& entry = sample_encryption_entries[i];
+      RCHECK(entry.Parse(&reader, iv_size, has_subsamples));
+#if BUILDFLAG(ENABLE_CBCS_ENCRYPTION_SCHEME)
+      // if we don't have a per-sample IV, get the constant IV.
+      if (!iv_size) {
+        RCHECK(ApplyConstantIv(i, entry));
+      }
+#endif
     }
     pos += info_size;
   }
 
   return true;
 }
 
 bool TrackRunIterator::IsRunValid() const {
   return run_itr_ != runs_.end();
 }
@@ skipping 96 matching lines @@
 }
 
 const TrackEncryption& TrackRunIterator::track_encryption() const {
   if (is_audio())
     return audio_description().sinf.info.track_encryption;
   return video_description().sinf.info.track_encryption;
 }
 
 std::unique_ptr<DecryptConfig> TrackRunIterator::GetDecryptConfig() {
   DCHECK(is_encrypted());
+  size_t sample_idx = sample_itr_ - run_itr_->samples.begin();
+  const std::vector<uint8_t>& kid = GetKeyId(sample_idx);
 
   if (run_itr_->sample_encryption_entries.empty()) {
     DCHECK_EQ(0, aux_info_size());
+#if BUILDFLAG(ENABLE_CBCS_ENCRYPTION_SCHEME)
+    // The 'cbcs' scheme allows empty aux info when a constant IV is in use
+    // with full sample encryption. That case will fall through to here.
+    SampleEncryptionEntry sample_encryption_entry;
+    if (ApplyConstantIv(sample_idx, sample_encryption_entry)) {
+      return std::unique_ptr<DecryptConfig>(new DecryptConfig(
+          std::string(reinterpret_cast<const char*>(&kid[0]), kid.size()),
+          std::string(reinterpret_cast<const char*>(
+                          sample_encryption_entry.initialization_vector),
+                      arraysize(sample_encryption_entry.initialization_vector)),
+          sample_encryption_entry.subsamples));
+    }
+#endif
     MEDIA_LOG(ERROR, media_log_) << "Sample encryption info is not available.";
     return std::unique_ptr<DecryptConfig>();
   }
 
-  size_t sample_idx = sample_itr_ - run_itr_->samples.begin();
   DCHECK_LT(sample_idx, run_itr_->sample_encryption_entries.size());
   const SampleEncryptionEntry& sample_encryption_entry =
       run_itr_->sample_encryption_entries[sample_idx];
 
   size_t total_size = 0;
   if (!sample_encryption_entry.subsamples.empty() &&
       (!sample_encryption_entry.GetTotalSizeOfSubsamples(&total_size) ||
        total_size != static_cast<size_t>(sample_size()))) {
     MEDIA_LOG(ERROR, media_log_) << "Incorrect CENC subsample size.";
     return std::unique_ptr<DecryptConfig>();
   }
 
-  const std::vector<uint8_t>& kid = GetKeyId(sample_idx);
   return std::unique_ptr<DecryptConfig>(new DecryptConfig(
       std::string(reinterpret_cast<const char*>(&kid[0]), kid.size()),
       std::string(reinterpret_cast<const char*>(
                       sample_encryption_entry.initialization_vector),
                   arraysize(sample_encryption_entry.initialization_vector)),
       sample_encryption_entry.subsamples));
 }
 
 uint32_t TrackRunIterator::GetGroupDescriptionIndex(
     uint32_t sample_index) const {
@@ skipping 15 matching lines @@
   return (index == 0) ? track_encryption().default_kid
                       : GetSampleEncryptionInfoEntry(*run_itr_, index)->key_id;
 }
 
 uint8_t TrackRunIterator::GetIvSize(size_t sample_index) const {
   uint32_t index = GetGroupDescriptionIndex(sample_index);
   return (index == 0) ? track_encryption().default_iv_size
                       : GetSampleEncryptionInfoEntry(*run_itr_, index)->iv_size;
 }
 
+#if BUILDFLAG(ENABLE_CBCS_ENCRYPTION_SCHEME)
+bool TrackRunIterator::ApplyConstantIv(size_t sample_index,
+                                       SampleEncryptionEntry& entry) const {
+  if (!IsSampleEncrypted(sample_index))
+    return true;
+  uint32_t index = GetGroupDescriptionIndex(sample_index);
+  const uint8_t constant_iv_size =
+      index == 0
+          ? track_encryption().default_constant_iv_size
+          : GetSampleEncryptionInfoEntry(*run_itr_, index)->constant_iv_size;
+  RCHECK(constant_iv_size != 0);
+  const uint8_t* constant_iv =
+      index == 0 ? track_encryption().default_constant_iv
+                 : GetSampleEncryptionInfoEntry(*run_itr_, index)->constant_iv;
+  RCHECK(constant_iv != nullptr);
+  memcpy(entry.initialization_vector, constant_iv, constant_iv_size);

[kqyang, 2016/10/12 22:16:52]

It is safer to do:

memcpy(entry.initialization_vector, constant_iv, sizeof(constant_iv));

Since both entry.initialization_vector and constant_iv are 16-byte array; if
constant_iv_size is 8, the extra 8 bytes in constant_iv is zeroed, the extra 8
bytes in entry.initialization_vector should also be zeroed.

+  return true;
+}
+#endif
+
 }  // namespace mp4
 }  // namespace media