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diff --git a/third_party/libwebrtc/rtc_base/bitstream_reader.h b/third_party/libwebrtc/rtc_base/bitstream_reader.h
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+++ b/third_party/libwebrtc/rtc_base/bitstream_reader.h
@@ -0,0 +1,145 @@
+/*
+ *  Copyright 2021 The WebRTC Project Authors. All rights reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#ifndef RTC_BASE_BITSTREAM_READER_H_
+#define RTC_BASE_BITSTREAM_READER_H_
+
+#include <stdint.h>
+
+#include "absl/base/attributes.h"
+#include "absl/strings/string_view.h"
+#include "api/array_view.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/numerics/safe_conversions.h"
+
+namespace webrtc {
+
+// A class to parse sequence of bits. Byte order is assumed big-endian/network.
+// This class is optimized for successful parsing and binary size.
+// Individual calls to `Read` and `ConsumeBits` never fail. Instead they may
+// change the class state into 'failure state'. User of this class should verify
+// parsing by checking if class is in that 'failure state' by calling `Ok`.
+// That verification can be done once after multiple reads.
+class BitstreamReader {
+ public:
+  explicit BitstreamReader(
+      rtc::ArrayView<const uint8_t> bytes ABSL_ATTRIBUTE_LIFETIME_BOUND);
+  explicit BitstreamReader(
+      absl::string_view bytes ABSL_ATTRIBUTE_LIFETIME_BOUND);
+  BitstreamReader(const BitstreamReader&) = default;
+  BitstreamReader& operator=(const BitstreamReader&) = default;
+  ~BitstreamReader();
+
+  // Return number of unread bits in the buffer, or negative number if there
+  // was a reading error.
+  int RemainingBitCount() const;
+
+  // Returns `true` iff all calls to `Read` and `ConsumeBits` were successful.
+  bool Ok() const { return RemainingBitCount() >= 0; }
+
+  // Sets `BitstreamReader` into the failure state.
+  void Invalidate() { remaining_bits_ = -1; }
+
+  // Moves current read position forward. `bits` must be non-negative.
+  void ConsumeBits(int bits);
+
+  // Reads single bit. Returns 0 or 1.
+  ABSL_MUST_USE_RESULT int ReadBit();
+
+  // Reads `bits` from the bitstream. `bits` must be in range [0, 64].
+  // Returns an unsigned integer in range [0, 2^bits - 1].
+  // On failure sets `BitstreamReader` into the failure state and returns 0.
+  ABSL_MUST_USE_RESULT uint64_t ReadBits(int bits);
+
+  // Reads unsigned integer of fixed width.
+  template <typename T,
+            typename std::enable_if<std::is_unsigned<T>::value &&
+                                    !std::is_same<T, bool>::value &&
+                                    sizeof(T) <= 8>::type* = nullptr>
+  ABSL_MUST_USE_RESULT T Read() {
+    return rtc::dchecked_cast<T>(ReadBits(sizeof(T) * 8));
+  }
+
+  // Reads single bit as boolean.
+  template <
+      typename T,
+      typename std::enable_if<std::is_same<T, bool>::value>::type* = nullptr>
+  ABSL_MUST_USE_RESULT bool Read() {
+    return ReadBit() != 0;
+  }
+
+  // Reads value in range [0, `num_values` - 1].
+  // This encoding is similar to ReadBits(val, Ceil(Log2(num_values)),
+  // but reduces wastage incurred when encoding non-power of two value ranges
+  // Non symmetric values are encoded as:
+  // 1) n = bit_width(num_values)
+  // 2) k = (1 << n) - num_values
+  // Value v in range [0, k - 1] is encoded in (n-1) bits.
+  // Value v in range [k, num_values - 1] is encoded as (v+k) in n bits.
+  // https://aomediacodec.github.io/av1-spec/#nsn
+  uint32_t ReadNonSymmetric(uint32_t num_values);
+
+  // Reads exponential golomb encoded value.
+  // On failure sets `BitstreamReader` into the failure state and returns
+  // unspecified value.
+  // Exponential golomb values are encoded as:
+  // 1) x = source val + 1
+  // 2) In binary, write [bit_width(x) - 1] 0s, then x
+  // To decode, we count the number of leading 0 bits, read that many + 1 bits,
+  // and increment the result by 1.
+  // Fails the parsing if the value wouldn't fit in a uint32_t.
+  uint32_t ReadExponentialGolomb();
+
+  // Reads signed exponential golomb values at the current offset. Signed
+  // exponential golomb values are just the unsigned values mapped to the
+  // sequence 0, 1, -1, 2, -2, etc. in order.
+  // On failure sets `BitstreamReader` into the failure state and returns
+  // unspecified value.
+  int ReadSignedExponentialGolomb();
+
+ private:
+  void set_last_read_is_verified(bool value) const;
+
+  // Next byte with at least one unread bit.
+  const uint8_t* bytes_;
+
+  // Number of bits remained to read.
+  int remaining_bits_;
+
+  // Unused in release mode.
+  mutable bool last_read_is_verified_ = true;
+};
+
+inline BitstreamReader::BitstreamReader(rtc::ArrayView<const uint8_t> bytes)
+    : bytes_(bytes.data()), remaining_bits_(bytes.size() * 8) {}
+
+inline BitstreamReader::BitstreamReader(absl::string_view bytes)
+    : bytes_(reinterpret_cast<const uint8_t*>(bytes.data())),
+      remaining_bits_(bytes.size() * 8) {}
+
+inline BitstreamReader::~BitstreamReader() {
+  RTC_DCHECK(last_read_is_verified_) << "Latest calls to Read or ConsumeBit "
+                                        "were not checked with Ok function.";
+}
+
+inline void BitstreamReader::set_last_read_is_verified(bool value) const {
+#ifdef RTC_DCHECK_IS_ON
+  last_read_is_verified_ = value;
+#endif
+}
+
+inline int BitstreamReader::RemainingBitCount() const {
+  set_last_read_is_verified(true);
+  return remaining_bits_;
+}
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_BITSTREAM_READER_H_