Disregard trailing null bytes when locating RBSP stop bits.

media/filters/h264_bit_reader.cc

 // Copyright 2014 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 "base/logging.h"
 #include "media/filters/h264_bit_reader.h"
 
 namespace media {
 
 H264BitReader::H264BitReader()
@@ skipping 72 matching lines @@
   num_remaining_bits_in_curr_byte_ -= bits_left;
 
   return true;
 }
 
 off_t H264BitReader::NumBitsLeft() {
   return (num_remaining_bits_in_curr_byte_ + bytes_left_ * 8);
 }
 
 bool H264BitReader::HasMoreRBSPData() {
-  // Make sure we have more bits, if we are at 0 bits in current byte
-  // and updating current byte fails, we don't have more data anyway.
+  // Make sure we have more bits, if we are at 0 bits in current byte and
+  // updating current byte fails, we don't have more data anyway.
   if (num_remaining_bits_in_curr_byte_ == 0 && !UpdateCurrByte())
     return false;
 
-  // On last byte?
-  if (bytes_left_)
+  // If there is no more RBSP data, then |curr_byte_| contains the stop bit and
+  // zero padding. Check to see if there is other data instead.
+  // (We don't actually check for the stop bit itself, instead treating the
+  // invalid case of all trailing zeros identically).
+  if ((curr_byte_ & ((1 << (num_remaining_bits_in_curr_byte_ - 1)) - 1)) != 0)
     return true;
 
-  // Last byte, look for stop bit;
-  // We have more RBSP data if the last non-zero bit we find is not the
-  // first available bit.
-  return (curr_byte_ &
-          ((1 << (num_remaining_bits_in_curr_byte_ - 1)) - 1)) != 0;
+  // If there are remaining non-zero bytes, then there is more data. We don't
+  // handle emulation prevention sequences because it is non-sensical to use
+  // them when there is no data. (At least for PPS NAL units, which is the only

[Pawel Osciak, 2016/03/01 08:56:21]

I would perhaps remove the comment in parenthesis, we are not doing anything
specific only to PPS NALUs I believe.

[sandersd (OOO until July 31), 2016/03/17 19:07:51]

Done.

+  // case currently considered.)
+  if (bytes_left_) {

[Pawel Osciak, 2016/03/01 08:56:21]

This if could be dropped?

[sandersd (OOO until July 31), 2016/03/17 19:07:51]

Done.

+    for (off_t i = 0; i < bytes_left_; i++) {
+      if (data_[i] != 0)
+        return true;
+    }
+  }
+
+  bytes_left_ = 0;
+  return false;
 }
 
 size_t H264BitReader::NumEmulationPreventionBytesRead() {
   return emulation_prevention_bytes_;
 }
 
 }  // namespace media