Don't use ParsableBitArray to parse TS packet headers

Really low hanging fruit optimization for TS extraction.

ParsableBitArray is quite expensive. In particular readBits
contains at least 2 if blocks and a for loop, and was being
called 5 times per 188 byte packet (4 times via readBit). A
separate change will follow that optimizes readBit, but for
this particular case there's no real value to using a
ParsableBitArray anyway; use of ParsableBitArray IMO only
really becomes useful when you need to parse a bitstream more
than 4 bytes long, or where parsing the bitstream requires
some control flow (if/for) to parse.

There are probably other places where we're using
ParsableBitArray over-zealously. I'll roll that into a
tracking bug for looking in more detail at all extractors.

Issue: #3040

-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=161650940

library/core/src/main/java/com/google/android/exoplayer2/extractor/ts/TsExtractor.java

@@ -111,7 +111,6 @@ public Extractor[] createExtractors() {
  @Mode private final int mode;
  private final List<TimestampAdjuster> timestampAdjusters;
  private final ParsableByteArray tsPacketBuffer;
- private final ParsableBitArray tsScratch;
  private final SparseIntArray continuityCounters;
  private final TsPayloadReader.Factory payloadReaderFactory;
  private final SparseArray<TsPayloadReader> tsPayloadReaders; // Indexed by pid
@@ -164,7 +163,6 @@ public TsExtractor(@Mode int mode, TimestampAdjuster timestampAdjuster,
  timestampAdjusters.add(timestampAdjuster);
  }
  tsPacketBuffer = new ParsableByteArray(BUFFER_SIZE);
- tsScratch = new ParsableBitArray(new byte[3]);
  trackIds = new SparseBooleanArray();
  tsPayloadReaders = new SparseArray<>();
  continuityCounters = new SparseIntArray();
@@ -250,24 +248,23 @@ public int read(ExtractorInput input, PositionHolder seekPosition)
  return RESULT_CONTINUE;
  }
 
- tsPacketBuffer.skipBytes(1);
- tsPacketBuffer.readBytes(tsScratch, 3);
- if (tsScratch.readBit()) { // transport_error_indicator
+ int tsPacketHeader = tsPacketBuffer.readInt();
+ if ((tsPacketHeader & 0x800000) != 0) { // transport_error_indicator
  // There are uncorrectable errors in this packet.
  tsPacketBuffer.setPosition(endOfPacket);
  return RESULT_CONTINUE;
  }
- boolean payloadUnitStartIndicator = tsScratch.readBit();
- tsScratch.skipBits(1); // transport_priority
- int pid = tsScratch.readBits(13);
- tsScratch.skipBits(2); // transport_scrambling_control
- boolean adaptationFieldExists = tsScratch.readBit();
- boolean payloadExists = tsScratch.readBit();
+ boolean payloadUnitStartIndicator = (tsPacketHeader & 0x400000) != 0;
+ // Ignoring transport_priority (tsPacketHeader & 0x200000)
+ int pid = (tsPacketHeader & 0x1FFF00) >> 8;
+ // Ignoring transport_scrambling_control (tsPacketHeader & 0xC0)
+ boolean adaptationFieldExists = (tsPacketHeader & 0x20) != 0;
+ boolean payloadExists = (tsPacketHeader & 0x10) != 0;
 
  // Discontinuity check.
  boolean discontinuityFound = false;
- int continuityCounter = tsScratch.readBits(4);
  if (mode != MODE_HLS) {
+ int continuityCounter = tsPacketHeader & 0xF;
  int previousCounter = continuityCounters.get(pid, continuityCounter - 1);
  continuityCounters.put(pid, continuityCounter);
  if (previousCounter == continuityCounter) {
@@ -276,7 +273,7 @@ public int read(ExtractorInput input, PositionHolder seekPosition)
  tsPacketBuffer.setPosition(endOfPacket);
  return RESULT_CONTINUE;
  }
- } else if (continuityCounter != (previousCounter + 1) % 16) {
+ } else if (continuityCounter != ((previousCounter + 1) & 0xF)) {
  discontinuityFound = true;
  }
  }
@@ -296,7 +293,6 @@ public int read(ExtractorInput input, PositionHolder seekPosition)
  }
  tsPacketBuffer.setLimit(endOfPacket);
  payloadReader.consume(tsPacketBuffer, payloadUnitStartIndicator);
- Assertions.checkState(tsPacketBuffer.getPosition() <= endOfPacket);
  tsPacketBuffer.setLimit(limit);
  }
  }