media: Supports Clear Key key system for mojo CDM/Renderer combo

media/mojo/clients/mojo_cdm_factory.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 "media/mojo/clients/mojo_cdm_factory.h"
 
 #include "base/bind.h"
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
@@ skipping 23 matching lines @@
     const SessionExpirationUpdateCB& session_expiration_update_cb,
     const CdmCreatedCB& cdm_created_cb) {
   DVLOG(2) << __FUNCTION__ << ": " << key_system;
 
   if (!security_origin.is_valid()) {
     base::ThreadTaskRunnerHandle::Get()->PostTask(
         FROM_HERE, base::Bind(cdm_created_cb, nullptr, "Invalid origin."));
     return;
   }
 
+// When MojoRenderer is used, the real Renderer is running in a remote process,
+// which cannot use an AesDecryptor running locally. In this case, always
+// create the MojoCdm, giving the remote CDM a chance to handle |key_system|.
+// Note: We should not run AesDecryptor in the browser process except for
+// testing. See http://crbug.com/441957
+#if !defined(ENABLE_MOJO_RENDERER)

[yucliu1, 2016/11/11 21:44:38]

Can we have mojo cdm without mojo renderer?

[xhwang, 2016/11/11 21:45:54]

Yes, MojoCdm can work with the existing local RendererImpl through
MojoDecryptor. This is the plan for desktop CDM.

   if (CanUseAesDecryptor(key_system)) {
     scoped_refptr<MediaKeys> cdm(
         new AesDecryptor(security_origin, session_message_cb, session_closed_cb,

[yucliu1, 2016/11/12 00:26:24]

I remember the AesDecryptor::GetCdmId returns kInvalidCdmId which may breaks
some assumption:

https://cs.chromium.org/chromium/src/media/mojo/clients/mojo_audio_decoder.cc...

https://cs.chromium.org/chromium/src/media/filters/gpu_video_decoder.cc?sq=pa...

[xhwang, 2016/11/12 00:30:01]

These are all remote decoders, which will not work with AesDecryptor directly.
In this cease, usually we use DecryptingDemuxerStream to decrypt in the render
process directly, then what the decoders get will be clear (unencrypted) stream:

https://cs.chromium.org/chromium/src/media/filters/decoder_selector.cc?rcl=0&...

                          session_keys_change_cb));
     base::ThreadTaskRunnerHandle::Get()->PostTask(
         FROM_HERE, base::Bind(cdm_created_cb, cdm, ""));
     return;
   }
+#endif
 
   mojom::ContentDecryptionModulePtr cdm_ptr;
   service_manager::GetInterface<mojom::ContentDecryptionModule>(
       interface_provider_, &cdm_ptr);
 
   MojoCdm::Create(key_system, security_origin, cdm_config, std::move(cdm_ptr),
                   session_message_cb, session_closed_cb, session_keys_change_cb,
                   session_expiration_update_cb, cdm_created_cb);
 }
 
 }  // namespace media