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Disregard trailing null bytes when locating RBSP stop bit 

This is a more faithful implementation of more_rbsp_data().

There could be trailing null bytes in NAL units. This isn't valid per
H264 specification, but the referenced bug includes a sample where the
PPS in the avcC record includes a trailing null byte.

Workaround the problem so packager does not fail.

A similar problem is workarounded in Chrome:
https://codereview.chromium.org/1107593004

Closes #418

Change-Id: I28cb8a9371945dc094f766c3e559d7a66859b451
This commit is contained in:
KongQun Yang 2018-06-26 11:48:47 -07:00
parent 64f7a1bb4e
commit 577c219fb4
2 changed files with 42 additions and 9 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

35
packager/media/codecs/h26x_bit_reader.cc
View File

@ -7,6 +7,14 @@
namespace shaka {
namespace media {
namespace {
// Check if any bits in the least significant |valid_bits| are set to 1.
bool CheckAnyBitsSet(int byte, int valid_bits) {
return (byte & ((1 << valid_bits) - 1)) != 0;
}
} // namespace
H26xBitReader::H26xBitReader()
: data_(NULL),
@ -145,20 +153,29 @@ off_t H26xBitReader::NumBitsLeft() {
}
bool H26xBitReader::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 the remaining bits is the stop bit
// followed by zero paddings. So if there are 1s in the remaining bits
// excluding the current bit, then the current bit is not a stop bit,
// regardless of whether it is 1 or not. Therefore there is more data.
if (CheckAnyBitsSet(curr_byte_, num_remaining_bits_in_curr_byte_ - 1))
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;
// While the spec disallows it (7.4.1: "The last byte of the NAL unit shall
// not be equal to 0x00"), some streams have trailing null bytes anyway. We
// don't handle emulation prevention sequences because HasMoreRBSPData() is
// not used when parsing slices (where cabac_zero_word elements are legal).
for (off_t i = 0; i < bytes_left_; i++) {
if (data_[i] != 0)
return true;
}
bytes_left_ = 0;
return false;
}
size_t H26xBitReader::NumEmulationPreventionBytesRead() {

16
packager/media/codecs/h26x_bit_reader_unittest.cc
View File

@ -42,6 +42,22 @@ TEST(H26xBitReaderTest, ReadStreamWithoutEscapeAndTrailingZeroBytes) {
EXPECT_FALSE(reader.HasMoreRBSPData());
}
TEST(H26xBitReaderTest, ReadPpsWithTrailingZeroByte) {
H26xBitReader reader;
// Data copied from https://github.com/google/shaka-packager/issues/418.
const unsigned char pps_rbsp[] = {0xee, 0x3c, 0x80, 0x00};
EXPECT_TRUE(reader.Initialize(pps_rbsp, sizeof(pps_rbsp)));
// Skips all the fields in PPS (kind of simulates ParsePps).
EXPECT_TRUE(reader.SkipBits(16));
EXPECT_EQ(reader.NumBitsLeft(), 16);
// The remaining data is '80 00'. The trailing null byte is ignored. There
// are no bits before the stop bit, so there is no more RBSP data.
EXPECT_FALSE(reader.HasMoreRBSPData());
}
TEST(H26xBitReaderTest, SingleByteStream) {
H26xBitReader reader;
const unsigned char rbsp[] = {0x18};