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/*
* Copyright (c) 2015 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.
*/
#include "modules/video_coding/utility/vp8_header_parser.h"
#include "rtc_base/logging.h"
#include "rtc_base/system/arch.h"
namespace webrtc {
namespace vp8 {
namespace {
const size_t kCommonPayloadHeaderLength = 3;
const size_t kKeyPayloadHeaderLength = 10;
} // namespace
static uint32_t BSwap32(uint32_t x) {
return (x >> 24) | ((x >> 8) & 0xff00) | ((x << 8) & 0xff0000) | (x << 24);
}
static void VP8LoadFinalBytes(VP8BitReader* const br) {
// Only read 8bits at a time.
if (br->buf_ < br->buf_end_) {
br->bits_ += 8;
br->value_ = static_cast<uint32_t>(*br->buf_++) | (br->value_ << 8);
} else if (!br->eof_) {
br->value_ <<= 8;
br->bits_ += 8;
br->eof_ = 1;
}
}
static void VP8LoadNewBytes(VP8BitReader* const br) {
int BITS = 24;
// Read 'BITS' bits at a time.
if (br->buf_ + sizeof(uint32_t) <= br->buf_end_) {
uint32_t bits;
const uint32_t in_bits = *(const uint32_t*)(br->buf_);
br->buf_ += BITS >> 3;
#if defined(WEBRTC_ARCH_BIG_ENDIAN)
bits = static_cast<uint32_t>(in_bits);
if (BITS != 8 * sizeof(uint32_t))
bits >>= (8 * sizeof(uint32_t) - BITS);
#else
bits = BSwap32(in_bits);
bits >>= 32 - BITS;
#endif
br->value_ = bits | (br->value_ << BITS);
br->bits_ += BITS;
} else {
VP8LoadFinalBytes(br);
}
}
static void VP8InitBitReader(VP8BitReader* const br,
const uint8_t* const start,
const uint8_t* const end) {
br->range_ = 255 - 1;
br->buf_ = start;
br->buf_end_ = end;
br->value_ = 0;
br->bits_ = -8; // To load the very first 8bits.
br->eof_ = 0;
VP8LoadNewBytes(br);
}
// Read a bit with proba 'prob'.
static int VP8GetBit(VP8BitReader* const br, int prob) {
uint8_t range = br->range_;
if (br->bits_ < 0) {
VP8LoadNewBytes(br);
if (br->eof_)
return 0;
}
const int pos = br->bits_;
const uint8_t split = (range * prob) >> 8;
const uint8_t value = static_cast<uint8_t>(br->value_ >> pos);
int bit;
if (value > split) {
range -= split + 1;
br->value_ -= static_cast<uint32_t>(split + 1) << pos;
bit = 1;
} else {
range = split;
bit = 0;
}
if (range <= static_cast<uint8_t>(0x7e)) {
const int shift = kVP8Log2Range[range];
range = kVP8NewRange[range];
br->bits_ -= shift;
}
br->range_ = range;
return bit;
}
static uint32_t VP8GetValue(VP8BitReader* const br, int bits) {
uint32_t v = 0;
while (bits-- > 0) {
v |= VP8GetBit(br, 0x80) << bits;
}
return v;
}
static uint32_t VP8Get(VP8BitReader* const br) {
return VP8GetValue(br, 1);
}
static int32_t VP8GetSignedValue(VP8BitReader* const br, int bits) {
const int value = VP8GetValue(br, bits);
return VP8Get(br) ? -value : value;
}
static void ParseSegmentHeader(VP8BitReader* br) {
int use_segment = VP8Get(br);
if (use_segment) {
int update_map = VP8Get(br);
if (VP8Get(br)) {
int s;
VP8Get(br);
for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
VP8Get(br) ? VP8GetSignedValue(br, 7) : 0;
}
for (s = 0; s < NUM_MB_SEGMENTS; ++s) {
VP8Get(br) ? VP8GetSignedValue(br, 6) : 0;
}
}
if (update_map) {
int s;
for (s = 0; s < MB_FEATURE_TREE_PROBS; ++s) {
VP8Get(br) ? VP8GetValue(br, 8) : 255;
}
}
}
}
static void ParseFilterHeader(VP8BitReader* br) {
VP8Get(br);
VP8GetValue(br, 6);
VP8GetValue(br, 3);
int use_lf_delta = VP8Get(br);
if (use_lf_delta) {
if (VP8Get(br)) {
int i;
for (i = 0; i < NUM_REF_LF_DELTAS; ++i) {
if (VP8Get(br)) {
VP8GetSignedValue(br, 6);
}
}
for (i = 0; i < NUM_MODE_LF_DELTAS; ++i) {
if (VP8Get(br)) {
VP8GetSignedValue(br, 6);
}
}
}
}
}
bool GetQp(const uint8_t* buf, size_t length, int* qp) {
if (length < kCommonPayloadHeaderLength) {
RTC_LOG(LS_WARNING) << "Failed to get QP, invalid length.";
return false;
}
VP8BitReader br;
const uint32_t bits = buf[0] | (buf[1] << 8) | (buf[2] << 16);
int key_frame = !(bits & 1);
// Size of first partition in bytes.
uint32_t partition_length = (bits >> 5);
size_t header_length = kCommonPayloadHeaderLength;
if (key_frame) {
header_length = kKeyPayloadHeaderLength;
}
if (header_length + partition_length > length) {
RTC_LOG(LS_WARNING) << "Failed to get QP, invalid length: " << length;
return false;
}
buf += header_length;
VP8InitBitReader(&br, buf, buf + partition_length);
if (key_frame) {
// Color space and pixel type.
VP8Get(&br);
VP8Get(&br);
}
ParseSegmentHeader(&br);
ParseFilterHeader(&br);
// Number of coefficient data partitions.
VP8GetValue(&br, 2);
// Base QP.
const int base_q0 = VP8GetValue(&br, 7);
if (br.eof_ == 1) {
RTC_LOG(LS_WARNING) << "Failed to get QP, end of file reached.";
return false;
}
*qp = base_q0;
return true;
}
} // namespace vp8
} // namespace webrtc
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