blob: e5796be458c7d813163e0dde2a2a49286d957d4f [file] [log] [blame]
// 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 <stddef.h>
#include <algorithm>
#include "base/logging.h"
#include "base/macros.h"
#include "media/filters/h264_parser.h"
#include "media/video/h264_poc.h"
namespace media {
namespace {
// Check if a slice includes memory management control operation 5, which
// results in some |pic_order_cnt| state being cleared.
bool HasMMCO5(const media::H264SliceHeader& slice_hdr) {
// Require that the frame actually has memory management control operations.
if (slice_hdr.nal_ref_idc == 0 ||
slice_hdr.idr_pic_flag ||
!slice_hdr.adaptive_ref_pic_marking_mode_flag) {
return false;
}
for (size_t i = 0; i < arraysize(slice_hdr.ref_pic_marking); i++) {
int32_t op = slice_hdr.ref_pic_marking[i].memory_mgmnt_control_operation;
if (op == 5)
return true;
// Stop at the end of the list.
if (op == 0)
return false;
}
// Should not get here, the list is always zero terminated.
return false;
}
} // namespace
H264POC::H264POC() {
Reset();
}
H264POC::~H264POC() {}
void H264POC::Reset() {
// It shouldn't be necessary to reset these values, but doing so will improve
// reproducibility for buggy streams.
ref_pic_order_cnt_msb_ = 0;
ref_pic_order_cnt_lsb_ = 0;
prev_frame_num_ = 0;
prev_frame_num_offset_ = 0;
pending_mmco5_ = false;
}
base::Optional<int32_t> H264POC::ComputePicOrderCnt(
const H264SPS* sps,
const H264SliceHeader& slice_hdr) {
if (slice_hdr.field_pic_flag) {
DLOG(ERROR) << "Interlaced frames are not supported";
return base::nullopt;
}
int32_t pic_order_cnt = 0;
bool mmco5 = HasMMCO5(slice_hdr);
int32_t max_frame_num = 1 << (sps->log2_max_frame_num_minus4 + 4);
int32_t max_pic_order_cnt_lsb =
1 << (sps->log2_max_pic_order_cnt_lsb_minus4 + 4);
// Based on T-REC-H.264 8.2.1, "Decoding process for picture order
// count", available from http://www.itu.int/rec/T-REC-H.264.
//
// Reorganized slightly from spec pseudocode to handle MMCO5 when storing
// state instead of when loading it.
//
// Note: Gaps in frame numbers are ignored. They do not affect POC
// computation.
switch (sps->pic_order_cnt_type) {
case 0: {
int32_t prev_pic_order_cnt_msb = ref_pic_order_cnt_msb_;
int32_t prev_pic_order_cnt_lsb = ref_pic_order_cnt_lsb_;
// For an IDR picture, clear the state.
if (slice_hdr.idr_pic_flag) {
prev_pic_order_cnt_msb = 0;
prev_pic_order_cnt_lsb = 0;
}
// 8-3. Derive |pic_order_cnt_msb|, accounting for wrapping which is
// detected when |pic_order_cnt_lsb| increases or decreases by at
// least half of its maximum.
int32_t pic_order_cnt_msb;
if ((slice_hdr.pic_order_cnt_lsb < prev_pic_order_cnt_lsb) &&
(prev_pic_order_cnt_lsb - slice_hdr.pic_order_cnt_lsb >=
max_pic_order_cnt_lsb / 2)) {
pic_order_cnt_msb = prev_pic_order_cnt_msb + max_pic_order_cnt_lsb;
} else if ((slice_hdr.pic_order_cnt_lsb > prev_pic_order_cnt_lsb) &&
(slice_hdr.pic_order_cnt_lsb - prev_pic_order_cnt_lsb >
max_pic_order_cnt_lsb / 2)) {
pic_order_cnt_msb = prev_pic_order_cnt_msb - max_pic_order_cnt_lsb;
} else {
pic_order_cnt_msb = prev_pic_order_cnt_msb;
}
// 8-4, 8-5. Derive |top_field_order_count| and |bottom_field_order_cnt|
// (assuming no interlacing).
int32_t top_foc = pic_order_cnt_msb + slice_hdr.pic_order_cnt_lsb;
int32_t bottom_foc = top_foc + slice_hdr.delta_pic_order_cnt_bottom;
// Compute POC.
//
// MMCO5, like IDR, starts a new reordering group. The POC is specified to
// change to 0 after decoding; we change it immediately and set the
// |pending_mmco5_| flag.
if (mmco5)
pic_order_cnt = 0;
else
pic_order_cnt = std::min(top_foc, bottom_foc);
// Store state.
pending_mmco5_ = mmco5;
prev_frame_num_ = slice_hdr.frame_num;
if (slice_hdr.nal_ref_idc != 0) {
if (mmco5) {
ref_pic_order_cnt_msb_ = 0;
ref_pic_order_cnt_lsb_ = top_foc;
} else {
ref_pic_order_cnt_msb_ = pic_order_cnt_msb;
ref_pic_order_cnt_lsb_ = slice_hdr.pic_order_cnt_lsb;
}
}
break;
}
case 1: {
// 8-6. Derive |frame_num_offset|.
int32_t frame_num_offset;
if (slice_hdr.idr_pic_flag)
frame_num_offset = 0;
else if (prev_frame_num_ > slice_hdr.frame_num)
frame_num_offset = prev_frame_num_offset_ + max_frame_num;
else
frame_num_offset = prev_frame_num_offset_;
// 8-7. Derive |abs_frame_num|.
int32_t abs_frame_num;
if (sps->num_ref_frames_in_pic_order_cnt_cycle != 0)
abs_frame_num = frame_num_offset + slice_hdr.frame_num;
else
abs_frame_num = 0;
if (slice_hdr.nal_ref_idc == 0 && abs_frame_num > 0)
abs_frame_num--;
// 8-9. Derive |expected_pic_order_cnt| (the |pic_order_cnt| indicated
// by the cycle described in the SPS).
int32_t expected_pic_order_cnt = 0;
if (abs_frame_num > 0) {
// 8-8. Derive pic_order_cnt_cycle_cnt and
// frame_num_in_pic_order_cnt_cycle.
// Moved inside 8-9 to avoid division when this check is not done.
if (sps->num_ref_frames_in_pic_order_cnt_cycle == 0) {
DLOG(ERROR) << "Invalid num_ref_frames_in_pic_order_cnt_cycle";
return base::nullopt;
}
// H264Parser checks that num_ref_frames_in_pic_order_cnt_cycle < 255.
int32_t pic_order_cnt_cycle_cnt =
(abs_frame_num - 1) / sps->num_ref_frames_in_pic_order_cnt_cycle;
int32_t frame_num_in_pic_order_cnt_cycle =
(abs_frame_num - 1) % sps->num_ref_frames_in_pic_order_cnt_cycle;
// 8-9 continued.
expected_pic_order_cnt = pic_order_cnt_cycle_cnt *
sps->expected_delta_per_pic_order_cnt_cycle;
for (int32_t i = 0; i <= frame_num_in_pic_order_cnt_cycle; i++)
expected_pic_order_cnt += sps->offset_for_ref_frame[i];
}
if (slice_hdr.nal_ref_idc == 0)
expected_pic_order_cnt += sps->offset_for_non_ref_pic;
// 8-10. Derive |top_field_order_cnt| and |bottom_field_order_cnt|
// (assuming no interlacing).
int32_t top_foc = expected_pic_order_cnt + slice_hdr.delta_pic_order_cnt0;
int32_t bottom_foc = top_foc + sps->offset_for_top_to_bottom_field +
slice_hdr.delta_pic_order_cnt1;
// Compute POC. MMCO5 handling is the same as |pic_order_cnt_type| == 0.
if (mmco5)
pic_order_cnt = 0;
else
pic_order_cnt = std::min(top_foc, bottom_foc);
// Store state.
pending_mmco5_ = mmco5;
prev_frame_num_ = slice_hdr.frame_num;
if (mmco5)
prev_frame_num_offset_ = 0;
else
prev_frame_num_offset_ = frame_num_offset;
break;
}
case 2: {
// 8-11. Derive |frame_num_offset|.
int32_t frame_num_offset;
if (slice_hdr.idr_pic_flag)
frame_num_offset = 0;
else if (prev_frame_num_ > slice_hdr.frame_num)
frame_num_offset = prev_frame_num_offset_ + max_frame_num;
else
frame_num_offset = prev_frame_num_offset_;
// 8-12, 8-13. Derive |temp_pic_order_count| (it's always the
// |pic_order_cnt|, regardless of interlacing).
int32_t temp_pic_order_count;
if (slice_hdr.idr_pic_flag)
temp_pic_order_count = 0;
else if (slice_hdr.nal_ref_idc == 0)
temp_pic_order_count = 2 * (frame_num_offset + slice_hdr.frame_num) - 1;
else
temp_pic_order_count = 2 * (frame_num_offset + slice_hdr.frame_num);
// Compute POC. MMCO5 handling is the same as |pic_order_cnt_type| == 0.
if (mmco5)
pic_order_cnt = 0;
else
pic_order_cnt = temp_pic_order_count;
// Store state.
pending_mmco5_ = mmco5;
prev_frame_num_ = slice_hdr.frame_num;
if (mmco5)
prev_frame_num_offset_ = 0;
else
prev_frame_num_offset_ = frame_num_offset;
break;
}
default:
DLOG(ERROR) << "Invalid pic_order_cnt_type: " << sps->pic_order_cnt_type;
return base::nullopt;
}
return pic_order_cnt;
}
} // namespace media