Add back prefix parser. (#171)

Author: jianjunz

common_video/BUILD.gn

@@ -23,6 +23,8 @@ rtc_library("common_video") {
     "h264/h264_common.h",
     "h264/pps_parser.cc",
     "h264/pps_parser.h",
+    "h264/prefix_parser.cc",
+    "h264/prefix_parser.h",
     "h264/sps_parser.cc",
     "h264/sps_parser.h",
     "h264/sps_vui_rewriter.cc",

common_video/h264/prefix_parser.cc

@@ -14,7 +14,7 @@
 #include <vector>
 
 #include "common_video/h264/h264_common.h"
-#include "rtc_base/bit_buffer.h"
+#include "rtc_base/bitstream_reader.h"
 
 namespace {
 typedef absl::optional<webrtc::PrefixParser::PrefixState> OptionalPrefix;
@@ -38,46 +38,42 @@ PrefixParser::PrefixState::~PrefixState() = default;
 // Unpack RBSP and parse SVC extension state from the supplied buffer.
 absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefix(
     const uint8_t* data,
-                                                        size_t length) {
+    size_t length) {
   std::vector<uint8_t> unpacked_buffer = H264::ParseRbsp(data, length);
-  rtc::BitBuffer bit_buffer(unpacked_buffer.data(), unpacked_buffer.size());
-  return ParsePrefixUpToSvcExtension(&bit_buffer);
+    BitstreamReader reader(unpacked_buffer);
+  return ParsePrefixUpToSvcExtension(reader);
 }
 
-absl::optional<PrefixParser::PrefixState> PrefixParser::ParsePrefixUpToSvcExtension(
-    rtc::BitBuffer* buffer) {
+absl::optional<PrefixParser::PrefixState>
+PrefixParser::ParsePrefixUpToSvcExtension(BitstreamReader& reader) {
   // Now, we need to use a bit buffer to parse through the actual SVC extension
   // format. See Section 7.3.1 ("NAL unit syntax") and 7.3.1.1 ("NAL unit header
   // SVC extension syntax") of the H.264 standard for a complete description.
-
   PrefixState svc_extension;
 
-  uint32_t svc_extension_flag = 0;
   // Make sure the svc_extension_flag is on.
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension_flag, 1));
+  bool svc_extension_flag = reader.ReadBit();
   if (!svc_extension_flag)
     return OptionalPrefix();
 
   // idr_flag: u(1)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.idr_flag, 1));
+  svc_extension.idr_flag = reader.Read<bool>();
   // priority_id: u(6)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.priority_id, 6));
+  svc_extension.priority_id = reader.ReadBits(6);
   // no_inter_layer_pred_flag: u(1)
-  RETURN_EMPTY_ON_FAIL(
-      buffer->ReadBits(&svc_extension.no_inter_layer_pred_flag, 1));
+  svc_extension.no_inter_layer_pred_flag = reader.Read<bool>();
   // dependency_id: u(3)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.dependency_id, 3));
+  svc_extension.dependency_id = reader.ReadBits(3);
   // quality_id: u(4)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.quality_id, 4));
+  svc_extension.quality_id = reader.ReadBits(4);
   // temporal_id: u(3)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.temporal_id, 3));
+  svc_extension.temporal_id = reader.ReadBits(3);
   // use_ref_base_pic_flag: u(1)
-  RETURN_EMPTY_ON_FAIL(
-      buffer->ReadBits(&svc_extension.use_ref_base_pic_flag, 1));
+  svc_extension.use_ref_base_pic_flag = reader.Read<bool>();
   // discardable_flag: u(1)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.discardable_flag, 1));
+  svc_extension.discardable_flag = reader.Read<bool>();
   // output_flag: u(1)
-  RETURN_EMPTY_ON_FAIL(buffer->ReadBits(&svc_extension.output_flag, 1));
+  svc_extension.output_flag = reader.Read<bool>();
 
   return OptionalPrefix(svc_extension);
 }

common_video/h264/prefix_parser.h

@@ -12,10 +12,7 @@
 #define COMMON_VIDEO_H264_PREFIX_PARSER_H_
 
 #include "absl/types/optional.h"
-
-namespace rtc {
-class BitBuffer;
-}
+#include "rtc_base/bitstream_reader.h"
 
 namespace webrtc {
 
@@ -44,9 +41,10 @@ class PrefixParser {
   static absl::optional<PrefixState> ParsePrefix(const uint8_t* data, size_t length);
 
  protected:
-  // Parse the prefix NAL, up till the SVC extension part, for a bit buffer where RBSP
-  // decoding has already been performed.
-  static absl::optional<PrefixState> ParsePrefixUpToSvcExtension(rtc::BitBuffer* buffer);
+  // Parse the prefix NAL, up till the SVC extension part, for a bit buffer
+  // where RBSP decoding has already been performed.
+  static absl::optional<PrefixState> ParsePrefixUpToSvcExtension(
+      BitstreamReader& reader);
 };
 
 }  // namespace webrtc