Chromecast PSSH boxes must use data_size parameter.

chromecast/media/cdm/chromecast_init_data.cc

 // 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.
 
 #include "chromecast/media/cdm/chromecast_init_data.h"
 
 #include "base/logging.h"
 #include "media/base/bit_reader.h"
 
 namespace chromecast {
@@ skipping 89 matching lines @@
 
     ::media::BitReader systemIdReader(&init_data[reader.bits_read() / 8],
                                       box_size - box_bytes_read);
     if (!IsChromecastSystemId(systemIdReader)) {
       reader.SkipBits((box_size - box_bytes_read) * 8);
       continue;
     }
     RCHECK(reader.SkipBits(16 * 8));
     box_bytes_read += 16;
 
+    uint32_t data_size;
+    RCHECK(reader.ReadBits(4 * 8, &data_size));
+    box_bytes_read += 4;
+    RCHECK(data_size == box_size - box_bytes_read);

[lcwu1, 2015/06/09 18:22:22]

Are we adding a new data_size field in the custom data? Why do we need this?

I am fine with that, but if so, we will need to communicate that with devrel and
tam teams. 

[gunsch, 2015/06/09 18:54:13]

We are not, and even if we were this does not affect anything for content
partners.

1) The way we communicate CustomData to our plugin is an internal implementation
detail negotiated between MPL and cast_shell.

2) PSSH boxes *must* have a four-byte data_size field (per the CENC spec) at
this location, even though that duplicates information about the rest of the
box. So this was actually a bug in my first implementation---not realizing this
difference about PSSH boxes in particular as opposed to the UUID box we were
using previously.

+
     uint16_t msg_type;
     RCHECK(reader.ReadBits(2 * 8, &msg_type));
     box_bytes_read += 2;
     RCHECK(msg_type < static_cast<uint16_t>(InitDataMessageType::END));
 
     chromecast_init_data_out->type = static_cast<InitDataMessageType>(msg_type);
     const uint8_t* data_start = &init_data[0] + reader.bits_read() / 8;
     chromecast_init_data_out->data.assign(
         data_start, data_start + box_size - box_bytes_read);
     return true;
   }
   return false;
 }
 
 }  // namespace media
 }  // namespace chromecast