Mpeg2 TS stream parser for media source.

media/mp2t/ts_section_psi.cc

+// Copyright (c) 2013 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/mp2t/ts_section_psi.h"
+
+#include "base/logging.h"
+#include "media/base/bit_reader.h"
+
+namespace media {
+namespace mp2t {
+
+class Mpeg2TsCrc {
+ public:
+  Mpeg2TsCrc();
+
+  // Update the CRC with 8 bits of |data|.
+  void Update(uint8 data);
+
+  bool IsValid();
+
+ private:
+  uint32 crc_;
+};
+
+Mpeg2TsCrc::Mpeg2TsCrc()
+    : crc_(0xffffffffu) {
+}
+
+void Mpeg2TsCrc::Update(uint8 data) {
+  const uint32_t kCrcPoly = 0x4c11db7;
+
+  // Align the bits to the MSB.
+  int nbits = 8;
+  uint32 data_msb_aligned = data;
+  data_msb_aligned <<= (32 - nbits);
+
+  while (nbits > 0) {
+    if ((data_msb_aligned ^ crc_) & 0x80000000) {
+      crc_ <<= 1;
+      crc_ ^= kCrcPoly;
+    } else {
+      crc_ <<= 1;
+    }
+
+    data_msb_aligned <<= 1;
+    nbits--;
+  }
+}
+
+bool Mpeg2TsCrc::IsValid() {
+  return (crc_ == 0);
+}
+
+TsSectionPsi::TsSectionPsi()
+    : wait_for_pusi_(true),
+      leading_bytes_to_discard_(0) {
+}
+
+TsSectionPsi::~TsSectionPsi() {
+}
+
+bool TsSectionPsi::Parse(bool payload_unit_start_indicator,
+                             const uint8* buf, int size) {
+  // Ignore partial PSI.
+  if (wait_for_pusi_ && !payload_unit_start_indicator)
+    return true;
+
+  if (payload_unit_start_indicator) {
+    // Reset the state of the PSI section.
+    ResetPsiState();
+
+    // Update the state.
+    wait_for_pusi_ = false;
+    DCHECK_GE(size, 1);
+    int pointer_field = buf[0];
+    leading_bytes_to_discard_ = pointer_field;
+    buf++;
+    size--;
+  }
+
+  // Discard some leading bytes if needed.
+  if (leading_bytes_to_discard_ > 0) {
+    int nbytes_to_discard = std::min(leading_bytes_to_discard_, size);
+    buf += nbytes_to_discard;
+    size -= nbytes_to_discard;
+    leading_bytes_to_discard_ -= nbytes_to_discard;
+  }
+  if (size == 0)
+    return true;
+
+  // Add the data to the parser state.
+  psi_byte_queue_.Push(buf, size);
+  int raw_psi_size;
+  const uint8* raw_psi;
+  psi_byte_queue_.Peek(&raw_psi, &raw_psi_size);
+
+  // Check whether we have enough data to start parsing.
+  if (raw_psi_size < 3)
+    return true;
+  int section_length =
+      ((static_cast<int>(raw_psi[1]) << 8) |
+       (static_cast<int>(raw_psi[2]))) & 0xfff;
+  if (section_length >= 1021)
+    return false;
+  int psi_length = section_length + 3;
+  if (raw_psi_size < psi_length) {
+    // Don't throw an error when there is not enough data,
+    // just wait for more data to come.
+    return true;
+  }
+
+  // There should not be any trailing bytes after a PMT.
+  // Instead, the pointer field should be used to stuff bytes.
+  DVLOG_IF(1, raw_psi_size > psi_length)
+      << "Trailing bytes after a PSI section: "
+      << psi_length << " vs " << raw_psi_size;
+
+  // Verify the CRC.
+  Mpeg2TsCrc crc;
+  for (int k = 0; k < psi_length; k++)

[acolwell GONE FROM CHROMIUM, 2013/09/16 06:19:30]

nit: Since this CRC class doesn't appear to be ever used anywhere else or
updated outside of this loop, perhaps just making this a helper function would
be better.

bool IsPsiCRCValid(const uint8* buf, int size)?

[damienv1, 2013/09/17 02:58:23]

Done.

+    crc.Update(raw_psi[k]);
+  if (!crc.IsValid())
+    return false;
+
+  // Parse the PSI section.
+  BitReader bit_reader(raw_psi, raw_psi_size);
+  bool status = ParsePsiSection(&bit_reader);
+  if (status)
+    ResetPsiState();
+
+  return status;
+}
+
+void TsSectionPsi::Flush() {
+}
+
+void TsSectionPsi::Reset() {
+  ResetPsiSection();
+  ResetPsiState();
+}
+
+void TsSectionPsi::ResetPsiState() {
+  wait_for_pusi_ = true;
+  psi_byte_queue_.Reset();
+  leading_bytes_to_discard_ = 0;
+}
+
+}  // namespace mp2t
+}  // namespace media
+