FFMPEG函數open_output_file()

FFMPEG代碼爲3.2 release版本， 文件位於ffmpeg_opt.c。

函數open_output_file()主要功能

打開輸出文件，而且給指針數組output_files賦值。若是存在的話給指針數組output_streams賦值。

open_output_file()函數中的代碼執行，不少都依賴於配置選項

即options[]中的內容。例如配置：

-to，影響值stop_time

-t，影響值recording_time

-ss，影響值start_time

-fs，影響值limit_filesize

-shortest，影響值shortest

-map，影響值nb_stream_maps

-vn，影響值video_disable

-an，影響值audio_disable

-sn，影響值subtitle_disable

-dn，影響值data_disable

註釋：

從FFMPEG release 3.2發現-dn沒有起做用，因此代碼有冗餘：

/* Data only if codec id match */
        if (!o->data_disable ) {
            enum AVCodecID codec_id = av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_DATA);
            for (i = 0; codec_id != AV_CODEC_ID_NONE && i < nb_input_streams; i++) {
                if (input_streams[i]->st->codecpar->codec_type == AVMEDIA_TYPE_DATA
                    && input_streams[i]->st->codecpar->codec_id == codec_id )
                    new_data_stream(o, oc, i);
            }
        }

-attach，影響值nb_attachments

OptionsContext int nb_metadata_map沒有賦值的地方，該代碼也是冗餘：

/* copy metadata */
    for (i = 0; i < o->nb_metadata_map; i++) {
        char *p;
        int in_file_index = strtol(o->metadata_map[i].u.str, &p, 0);

        if (in_file_index >= nb_input_files) {
            av_log(NULL, AV_LOG_FATAL, "Invalid input file index %d while processing metadata maps\n", in_file_index);
            exit_program(1);
        }
        copy_metadata(o->metadata_map[i].specifier, *p ? p + 1 : p, oc,
                      in_file_index >= 0 ?
                      input_files[in_file_index]->ctx : NULL, o);
    }

 

OptionsContext int nb_program沒有賦值的地方，該代碼也是冗餘：

/* process manually set programs */
    for (i = 0; i < o->nb_program; i++) {
        const char *p = o->program[i].u.str;
        int progid = i+1;
        AVProgram *program;

        while(*p) {
            const char *p2 = av_get_token(&p, ":");
            const char *to_dealloc = p2;
            char *key;
            if (!p2)
                break;

            if(*p) p++;

            key = av_get_token(&p2, "=");
            if (!key || !*p2) {
                av_freep(&to_dealloc);
                av_freep(&key);
                break;
            }
            p2++;

            if (!strcmp(key, "program_num"))
                progid = strtol(p2, NULL, 0);
            av_freep(&to_dealloc);
            av_freep(&key);
        }

        program = av_new_program(oc, progid);

        p = o->program[i].u.str;
        while(*p) {
            const char *p2 = av_get_token(&p, ":");
            const char *to_dealloc = p2;
            char *key;
            if (!p2)
                break;
            if(*p) p++;

            key = av_get_token(&p2, "=");
            if (!key) {
                av_log(NULL, AV_LOG_FATAL,
                       "No '=' character in program string %s.\n",
                       p2);
                exit_program(1);
            }
            if (!*p2)
                exit_program(1);
            p2++;

            if (!strcmp(key, "title")) {
                av_dict_set(&program->metadata, "title", p2, 0);
            } else if (!strcmp(key, "program_num")) {
            } else if (!strcmp(key, "st")) {
                int st_num = strtol(p2, NULL, 0);
                av_program_add_stream_index(oc, progid, st_num);
            } else {
                av_log(NULL, AV_LOG_FATAL, "Unknown program key %s.\n", key);
                exit_program(1);
            }
            av_freep(&to_dealloc);
            av_freep(&key);
        }
    }

OptionsContext int nb_metadata沒有賦值的地方，該代碼也是冗餘：

/* process manually set metadata */
    for (i = 0; i < o->nb_metadata; i++) {
        AVDictionary **m;
        char type, *val;
        const char *stream_spec;
        int index = 0, j, ret = 0;

        val = strchr(o->metadata[i].u.str, '=');
        if (!val) {
            av_log(NULL, AV_LOG_FATAL, "No '=' character in metadata string %s.\n",
                   o->metadata[i].u.str);
            exit_program(1);
        }
        *val++ = 0;

        parse_meta_type(o->metadata[i].specifier, &type, &index, &stream_spec);
        if (type == 's') {
            for (j = 0; j < oc->nb_streams; j++) {
                ost = output_streams[nb_output_streams - oc->nb_streams + j];
                if ((ret = check_stream_specifier(oc, oc->streams[j], stream_spec)) > 0) {
                    av_dict_set(&oc->streams[j]->metadata, o->metadata[i].u.str, *val ? val : NULL, 0);
                    if (!strcmp(o->metadata[i].u.str, "rotate")) {
                        ost->rotate_overridden = 1;
                    }
                } else if (ret < 0)
                    exit_program(1);
            }
        }
        else {
            switch (type) {
            case 'g':
                m = &oc->metadata;
                break;
            case 'c':
                if (index < 0 || index >= oc->nb_chapters) {
                    av_log(NULL, AV_LOG_FATAL, "Invalid chapter index %d in metadata specifier.\n", index);
                    exit_program(1);
                }
                m = &oc->chapters[index]->metadata;
                break;
            case 'p':
                if (index < 0 || index >= oc->nb_programs) {
                    av_log(NULL, AV_LOG_FATAL, "Invalid program index %d in metadata specifier.\n", index);
                    exit_program(1);
                }
                m = &oc->programs[index]->metadata;
                break;
            default:
                av_log(NULL, AV_LOG_FATAL, "Invalid metadata specifier %s.\n", o->metadata[i].specifier);
                exit_program(1);
            }
            av_dict_set(m, o->metadata[i].u.str, *val ? val : NULL, 0);
        }
    }

 

函數avformat_alloc_output_context2()

根據配置的輸出文件格式，獲取AVOutputFormat內容

函數new_video_stream()

若是輸出視頻數據的話，須要執行該函數

函數new_audio_stream()

若是輸出音頻數據的話，須要執行該函數

函數avio_open2()

打開輸出文件