| // 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/cxx17_backports.h" |
| #include "base/logging.h" |
| #include "media/video/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 < base::size(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() = default; |
| |
| 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; |
| } |
| |
| absl::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 absl::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 absl::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 absl::nullopt; |
| } |
| |
| return pic_order_cnt; |
| } |
| |
| } // namespace media |
