| /* |
| * MJPEG encoder |
| * Copyright (c) 2016 William Ma, Ted Ying, Jerry Jiang |
| * |
| * This file is part of FFmpeg. |
| * |
| * FFmpeg is free software; you can redistribute it and/or |
| * modify it under the terms of the GNU Lesser General Public |
| * License as published by the Free Software Foundation; either |
| * version 2.1 of the License, or (at your option) any later version. |
| * |
| * FFmpeg is distributed in the hope that it will be useful, |
| * but WITHOUT ANY WARRANTY; without even the implied warranty of |
| * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU |
| * Lesser General Public License for more details. |
| * |
| * You should have received a copy of the GNU Lesser General Public |
| * License along with FFmpeg; if not, write to the Free Software |
| * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA |
| */ |
| |
| #include <string.h> |
| #include <stdint.h> |
| #include <stdlib.h> |
| #include "libavutil/avassert.h" |
| #include "libavutil/common.h" |
| #include "libavutil/error.h" |
| #include "libavutil/qsort.h" |
| #include "mjpegenc_huffman.h" |
| |
| /** |
| * Comparison function for two PTables by prob |
| * |
| * @param a First PTable to compare |
| * @param b Second PTable to compare |
| * @return < 0 for less than, 0 for equals, > 0 for greater than |
| */ |
| static int compare_by_prob(const void *a, const void *b) |
| { |
| PTable a_val = *(PTable *) a; |
| PTable b_val = *(PTable *) b; |
| return a_val.prob - b_val.prob; |
| } |
| |
| /** |
| * Comparison function for two HuffTables by length |
| * |
| * @param a First HuffTable to compare |
| * @param b Second HuffTable to compare |
| * @return < 0 for less than, 0 for equals, > 0 for greater than |
| */ |
| static int compare_by_length(const void *a, const void *b) |
| { |
| HuffTable a_val = *(HuffTable *) a; |
| HuffTable b_val = *(HuffTable *) b; |
| return a_val.length - b_val.length; |
| } |
| |
| /** |
| * Computes the length of the Huffman encoding for each distinct input value. |
| * Uses package merge algorithm as follows: |
| * 1. start with an empty list, lets call it list(0), set i = 0 |
| * 2. add 1 entry to list(i) for each symbol we have and give each a score equal to the probability of the respective symbol |
| * 3. merge the 2 symbols of least score and put them in list(i+1), and remove them from list(i). The new score will be the sum of the 2 scores |
| * 4. if there is more than 1 symbol left in the current list(i), then goto 3 |
| * 5. i++ |
| * 6. if i < 16 goto 2 |
| * 7. select the n-1 elements in the last list with the lowest score (n = the number of symbols) |
| * 8. the length of the huffman code for symbol s will be equal to the number of times the symbol occurs in the select elements |
| * Go to guru.multimedia.cx/small-tasks-for-ffmpeg/ for more details |
| * |
| * All probabilities should be positive integers. The output is sorted by code, |
| * not by length. |
| * |
| * @param prob_table input array of a PTable for each distinct input value |
| * @param distincts output array of a HuffTable that will be populated by this function |
| * @param size size of the prob_table array |
| * @param max_length max length of an encoding |
| */ |
| void ff_mjpegenc_huffman_compute_bits(PTable *prob_table, HuffTable *distincts, int size, int max_length) |
| { |
| PackageMergerList list_a, list_b, *to = &list_a, *from = &list_b, *temp; |
| |
| int times, i, j, k; |
| |
| int nbits[257] = {0}; |
| |
| int min; |
| |
| av_assert0(max_length > 0); |
| |
| to->nitems = 0; |
| from->nitems = 0; |
| to->item_idx[0] = 0; |
| from->item_idx[0] = 0; |
| AV_QSORT(prob_table, size, PTable, compare_by_prob); |
| |
| for (times = 0; times <= max_length; times++) { |
| to->nitems = 0; |
| to->item_idx[0] = 0; |
| |
| j = 0; |
| k = 0; |
| |
| if (times < max_length) { |
| i = 0; |
| } |
| while (i < size || j + 1 < from->nitems) { |
| to->nitems++; |
| to->item_idx[to->nitems] = to->item_idx[to->nitems - 1]; |
| if (i < size && |
| (j + 1 >= from->nitems || |
| prob_table[i].prob < |
| from->probability[j] + from->probability[j + 1])) { |
| to->items[to->item_idx[to->nitems]++] = prob_table[i].value; |
| to->probability[to->nitems - 1] = prob_table[i].prob; |
| i++; |
| } else { |
| for (k = from->item_idx[j]; k < from->item_idx[j + 2]; k++) { |
| to->items[to->item_idx[to->nitems]++] = from->items[k]; |
| } |
| to->probability[to->nitems - 1] = |
| from->probability[j] + from->probability[j + 1]; |
| j += 2; |
| } |
| } |
| temp = to; |
| to = from; |
| from = temp; |
| } |
| |
| min = (size - 1 < from->nitems) ? size - 1 : from->nitems; |
| for (i = 0; i < from->item_idx[min]; i++) { |
| nbits[from->items[i]]++; |
| } |
| // we don't want to return the 256 bit count (it was just in here to prevent |
| // all 1s encoding) |
| j = 0; |
| for (i = 0; i < 256; i++) { |
| if (nbits[i] > 0) { |
| distincts[j].code = i; |
| distincts[j].length = nbits[i]; |
| j++; |
| } |
| } |
| } |
| |
| void ff_mjpeg_encode_huffman_init(MJpegEncHuffmanContext *s) |
| { |
| memset(s->val_count, 0, sizeof(s->val_count)); |
| } |
| |
| /** |
| * Produces a Huffman encoding with a given input |
| * |
| * @param s input to encode |
| * @param bits output array where the ith character represents how many input values have i length encoding |
| * @param val output array of input values sorted by their encoded length |
| * @param max_nval maximum number of distinct input values |
| */ |
| void ff_mjpeg_encode_huffman_close(MJpegEncHuffmanContext *s, uint8_t bits[17], |
| uint8_t val[], int max_nval) |
| { |
| int i, j; |
| int nval = 0; |
| PTable val_counts[257]; |
| HuffTable distincts[256]; |
| |
| for (i = 0; i < 256; i++) { |
| if (s->val_count[i]) nval++; |
| } |
| av_assert0 (nval <= max_nval); |
| |
| j = 0; |
| for (i = 0; i < 256; i++) { |
| if (s->val_count[i]) { |
| val_counts[j].value = i; |
| val_counts[j].prob = s->val_count[i]; |
| j++; |
| } |
| } |
| val_counts[j].value = 256; |
| val_counts[j].prob = 0; |
| ff_mjpegenc_huffman_compute_bits(val_counts, distincts, nval + 1, 16); |
| AV_QSORT(distincts, nval, HuffTable, compare_by_length); |
| |
| memset(bits, 0, sizeof(bits[0]) * 17); |
| for (i = 0; i < nval; i++) { |
| val[i] = distincts[i].code; |
| bits[distincts[i].length]++; |
| } |
| } |