h264_poc.cpp

// 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 "Util/logger.h"
#include <algorithm>
#include "macros.h"
#include "h264_parser.h"
#include "h264_poc.h"

using namespace ZL::Util;

namespace media {
    
    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;
    }
    
    // Check if a slice includes memory management control operation 5, which
    // results in some |pic_order_cnt| state being cleared.
    static 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;
    }
    
    bool H264POC::ComputePicOrderCnt(
                                     const H264SPS* sps,
                                     const H264SliceHeader& slice_hdr,
                                     int32_t *pic_order_cnt) {
        if (slice_hdr.field_pic_flag) {
            DebugL << "Interlaced frames are not supported";
            return false;
        }
        
        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);
        
        // Check for invalid (including duplicate) |frame_num| values. All cases are
        // treated as gaps, which is to say that nothing is done. (Gaps don't affect
        // POC computation.)
        if (!slice_hdr.idr_pic_flag &&
            slice_hdr.frame_num != (prev_frame_num_ + 1) % max_frame_num) {
            if (!sps->gaps_in_frame_num_value_allowed_flag){
                //WarnL << "Invalid gap in frame_num";
            }
        }
        
        // 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.
        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;
                *pic_order_cnt = min(top_foc, bottom_foc);
                
                // Store state.
                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) {
                        ErrorL << "Invalid num_ref_frames_in_pic_order_cnt_cycle";
                        return false;
                    }
                    
                    // 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;
                *pic_order_cnt = min(top_foc, bottom_foc);
                
                // Store state.
                prev_frame_num_ = slice_hdr.frame_num;
                prev_frame_num_offset_ = frame_num_offset;
                if (mmco5)
                    prev_frame_num_offset_ = 0;
                
                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).
                if (slice_hdr.idr_pic_flag)
                    *pic_order_cnt = 0;
                else if (slice_hdr.nal_ref_idc == 0)
                    *pic_order_cnt = 2 * (frame_num_offset + slice_hdr.frame_num) - 1;
                else
                    *pic_order_cnt = 2 * (frame_num_offset + slice_hdr.frame_num);
                
                // Store state.
                prev_frame_num_ = slice_hdr.frame_num;
                prev_frame_num_offset_ = frame_num_offset;
                if (mmco5)
                    prev_frame_num_offset_ = 0;
                
                break;
            }
                
            default:
                ErrorL << "Invalid pic_order_cnt_type: " << sps->pic_order_cnt_type;
                return false;
        }
        
        return true;
    }
    
}  // namespace media