media: Support better decoder switching

media/filters/decoder_selector.h

Index: media/filters/decoder_selector.h
diff --git a/media/filters/decoder_selector.h b/media/filters/decoder_selector.h
index 3ce4df6b201333d54617973dc02c8f7043a53598..0a30989b137db40c773f5c9a9bedce9b56ee4fd5 100644
--- a/media/filters/decoder_selector.h
+++ b/media/filters/decoder_selector.h
@@ -39,6 +39,11 @@ class MEDIA_EXPORT DecoderSelector {
   typedef typename StreamTraits::DecoderType Decoder;
   typedef typename StreamTraits::DecoderConfigType DecoderConfig;
 
+  // Callback to create a list of decoders to select from.
+  // TODO(xhwang): Use a DecoderFactory to create decoders one by one as needed,
+  // instead of creating a list of decoders all at once.
+  using CreateDecodersCB = base::RepeatingCallback<ScopedVector<Decoder>()>;
+
   // Indicates completion of Decoder selection.
   // - First parameter: The initialized Decoder. If it's set to NULL, then
   // Decoder initialization failed.
@@ -48,18 +53,17 @@ class MEDIA_EXPORT DecoderSelector {
   // Note: The caller owns selected Decoder and DecryptingDemuxerStream.
   // The caller should call DecryptingDemuxerStream::Reset() before
   // calling Decoder::Reset() to release any pending decryption or read.
-  typedef base::Callback<void(std::unique_ptr<Decoder>,
-                              std::unique_ptr<DecryptingDemuxerStream>)>
-      SelectDecoderCB;
+  using SelectDecoderCB =
+      base::Callback<void(std::unique_ptr<Decoder>,
+                          std::unique_ptr<DecryptingDemuxerStream>)>;
 
-  // |decoders| contains the Decoders to use when initializing.
   DecoderSelector(
-      const scoped_refptr<base::SingleThreadTaskRunner>& message_loop,
-      ScopedVector<Decoder> decoders,
+      const scoped_refptr<base::SingleThreadTaskRunner>& task_runner,
+      CreateDecodersCB create_decoders_cb,
       MediaLog* media_log);
 
   // Aborts pending Decoder selection and fires |select_decoder_cb| with
-  // NULL and NULL immediately if it's pending.
+  // null and null immediately if it's pending.
   ~DecoderSelector();
 
   // Initializes and selects the first Decoder that can decode the |stream|.
@@ -67,13 +71,20 @@ class MEDIA_EXPORT DecoderSelector {
   // the |select_decoder_cb|.
   // Notes:
   // 1. This must not be called again before |select_decoder_cb| is run.
-  // 2. Decoders that fail to initialize will be deleted. Future calls will
-  //    select from the decoders following the decoder that was last returned.
-  // 3. |cdm_context| is optional. If |cdm_context| is
-  //    null, no CDM will be available to perform decryption.
+  // 2. |create_decoders_cb| will be called to create a list of candidate
+  //    decoders to select from.
+  // 3. The |blacklisted_decoder| will be skipped in the decoder selection
+  //    process, unless DecryptingDemuxerStream is chosen. This is because
+  //    DecryptingDemuxerStream updates the |config_|, and the blacklist should
+  //    only be applied to the original |stream| config.
+  // 4. All decoders that are not selected will be deleted upon returning
+  //    |select_decoder_cb|.
+  // 5. |cdm_context| is optional. If |cdm_context| is null, no CDM will be
+  //    available to perform decryption.
   void SelectDecoder(StreamTraits* traits,
                      DemuxerStream* stream,
                      CdmContext* cdm_context,
+                     const std::string& blacklisted_decoder,
                      const SelectDecoderCB& select_decoder_cb,
                      const typename Decoder::OutputCB& output_cb,
                      const base::Closure& waiting_for_decryption_key_cb);
@@ -90,7 +101,7 @@ class MEDIA_EXPORT DecoderSelector {
   void ReturnNullDecoder();
 
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
-  ScopedVector<Decoder> decoders_;
+  CreateDecodersCB create_decoders_cb_;
   MediaLog* media_log_;
 
   StreamTraits* traits_;
@@ -100,10 +111,13 @@ class MEDIA_EXPORT DecoderSelector {
   DemuxerStream* input_stream_;
 
   CdmContext* cdm_context_;
+  std::string blacklisted_decoder_;
   SelectDecoderCB select_decoder_cb_;
   typename Decoder::OutputCB output_cb_;
   base::Closure waiting_for_decryption_key_cb_;
 
+  ScopedVector<Decoder> decoders_;
+
   std::unique_ptr<Decoder> decoder_;
   std::unique_ptr<DecryptingDemuxerStream> decrypted_stream_;