以MLT自带的Melt命令行工具源码为例
去掉一些不重要的代码

melt.c

int main(int argc, char **argv)
{int i;mlt_consumer consumer = NULL;FILE *store = NULL;char *name = NULL;mlt_profile profile = NULL;int is_progress = 0;int is_silent = 0;int is_abort = 0;int is_getc = 0;int error = 0;mlt_profile backup_profile;mlt_repository repo = NULL;const char *repo_path = NULL;int is_consumer_explicit = 0;int is_setlocale = 0;// Handle abnormal exit situations.signal(SIGSEGV, abnormal_exit_handler);signal(SIGILL, abnormal_exit_handler);signal(SIGABRT, abnormal_exit_handler);// 设置地区，不设置默认是中国// 在程序中，区域是影响程序语言处理方式的环境变量，比如日期，时间，货币，数字和字符串的格式等。for (i = 1; i < argc; i++) {if (!strcmp(argv[i], "-setlocale")) {is_setlocale = 1;break;}}for (i = 1; i < argc; i++) {// Check for serialisation switchif (!strcmp(argv[i], "-serialise")) {name = argv[++i];if (name != NULL && strstr(name, ".melt"))store = fopen(name, "w");else {if (name == NULL || name[0] == '-')store = stdout;name = NULL;}}// Look for the profile optionelse if (!strcmp(argv[i], "-profile")) {// Construct the factoryif (!repo)repo = setup_factory(repo_path, is_setlocale);const char *pname = argv[++i];if (pname && pname[0] != '-')profile = mlt_profile_init(pname);} else if (!strcmp(argv[i], "-progress")) {is_progress = 1;} else if (!strcmp(argv[i], "-progress2")) {is_progress = 2;}// 查找，会打印对应的service种类和信息// Look for the query optionelse if (!strcmp(argv[i], "-query")) {// Construct the factoryif (!repo)repo = setup_factory(repo_path, is_setlocale);const char *pname = argv[++i];if (pname && pname[0] != '-') {if (!strcmp(pname, "consumers") || !strcmp(pname, "consumer"))query_services(repo, mlt_service_consumer_type);else if (!strcmp(pname, "filters") || !strcmp(pname, "filter"))query_services(repo, mlt_service_filter_type);else if (!strcmp(pname, "links") || !strcmp(pname, "link"))query_services(repo, mlt_service_link_type);else if (!strcmp(pname, "producers") || !strcmp(pname, "producer"))query_services(repo, mlt_service_producer_type);else if (!strcmp(pname, "transitions") || !strcmp(pname, "transition"))query_services(repo, mlt_service_transition_type);else if (!strcmp(pname, "profiles") || !strcmp(pname, "profile"))query_profiles();else if (!strcmp(pname, "presets") || !strcmp(pname, "preset"))query_presets();else if (!strncmp(pname, "format", 6))query_formats();else if (!strncmp(pname, "acodec", 6) || !strcmp(pname, "audio_codecs"))query_acodecs();else if (!strncmp(pname, "vcodec", 6) || !strcmp(pname, "video_codecs"))query_vcodecs();else if (!strncmp(pname, "consumer=", 9))query_metadata(repo,mlt_service_consumer_type,"consumer",strchr(pname, '=') + 1);else if (!strncmp(pname, "filter=", 7))query_metadata(repo, mlt_service_filter_type, "filter", strchr(pname, '=') + 1);else if (!strncmp(pname, "link=", 5))query_metadata(repo, mlt_service_link_type, "link", strchr(pname, '=') + 1);else if (!strncmp(pname, "producer=", 9))query_metadata(repo,mlt_service_producer_type,"producer",strchr(pname, '=') + 1);else if (!strncmp(pname, "transition=", 11))query_metadata(repo,mlt_service_transition_type,"transition",strchr(pname, '=') + 1);else if (!strncmp(pname, "profile=", 8))query_profile(strchr(pname, '=') + 1);else if (!strncmp(pname, "preset=", 7))query_preset(strchr(pname, '=') + 1);elsegoto query_all;} else {query_all:query_services(repo, mlt_service_consumer_type);query_services(repo, mlt_service_filter_type);query_services(repo, mlt_service_link_type);query_services(repo, mlt_service_producer_type);query_services(repo, mlt_service_transition_type);fprintf(stdout,"# You can query the metadata for a specific service using:\n""# -query <type>=<identifier>\n""# where <type> is one of: consumer, filter, producer, or transition.\n");}goto exit_factory;} else if (!strcmp(argv[i], "-silent")) {is_silent = 1;} else if (!strcmp(argv[i], "-quiet")) {is_silent = 1;mlt_log_set_level(MLT_LOG_QUIET);} else if (!strcmp(argv[i], "-verbose")) {mlt_log_set_level(MLT_LOG_VERBOSE);} else if (!strcmp(argv[i], "-timings")) {mlt_log_set_level(MLT_LOG_TIMINGS);} else if (!strcmp(argv[i], "-version") || !strcmp(argv[i], "--version")) {fprintf(stdout,"%s " VERSION "\n""Copyright (C) 2002-2023 Meltytech, LLC\n""<https://www.mltframework.org/>\n""This is free software; see the source for copying conditions.  There is NO\n""warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.\n",basename(argv[0]));goto exit_factory;} else if (!strcmp(argv[i], "-debug")) {mlt_log_set_level(MLT_LOG_DEBUG);} else if (!strcmp(argv[i], "-abort")) {is_abort = 1;} else if (!strcmp(argv[i], "-getc")) {is_getc = 1;} else if (!repo && !strcmp(argv[i], "-repository")) {if (i + 1 < argc && argv[i + 1][0] != '-')repo_path = argv[++i];} else if (!strcmp(argv[i], "-consumer")) {is_consumer_explicit = 1;}}if (!is_silent && !isatty(STDIN_FILENO) && !is_progress)is_progress = 1;// Construct the factoryif (!repo)repo = setup_factory(repo_path, is_setlocale);// Create profile if not set explicitlyif (getenv("MLT_PROFILE"))// 根据环境变量去找到对应的profileprofile = mlt_profile_init(NULL);if (profile == NULL)profile = mlt_profile_init(NULL);elseprofile->is_explicit = 1;// 备份profile，然后加载consumer，如果profile在加载consumer的时候发生了改变，则表明这时候的profile信息是精确的// Look for the consumer option to load profile settings from consumer propertiesbackup_profile = mlt_profile_clone(profile);if (load_consumer(&consumer, profile, argc, argv) != EXIT_SUCCESS)goto exit_factory;// If the consumer changed the profile, then it is explicit.if (backup_profile && !profile->is_explicit&& (profile->width != backup_profile->width || profile->height != backup_profile->height|| profile->sample_aspect_num != backup_profile->sample_aspect_num|| profile->sample_aspect_den != backup_profile->sample_aspect_den|| profile->frame_rate_den != backup_profile->frame_rate_den|| profile->frame_rate_num != backup_profile->frame_rate_num|| profile->colorspace != backup_profile->colorspace))profile->is_explicit = 1;mlt_profile_close(backup_profile);backup_profile = NULL;// 除了第一个参数，把后面的参数都传递到factory中，用于生产producer// Get melt producerif (argc > 1)melt = mlt_factory_producer(profile, "melt", &argv[1]);if (melt) {// Generate an automatic profile if needed.if (!profile->is_explicit) {mlt_producer first_producer = mlt_properties_get_data(MLT_PRODUCER_PROPERTIES(melt),"first_producer",NULL);mlt_profile_from_producer(profile, first_producer);mlt_consumer melt_consumer = MLT_CONSUMER(mlt_service_consumer(MLT_PRODUCER_SERVICE(melt)));if (melt_consumer)mlt_consumer_connect(melt_consumer, NULL);mlt_producer_close(melt);melt = mlt_factory_producer(profile, "melt", &argv[1]);}double scale = mlt_properties_get_double(MLT_CONSUMER_PROPERTIES(consumer), "scale");if (scale > 0.0) {// 设置缩放set_preview_scale(&profile, &backup_profile, scale);}// Reload the consumer with the fully qualified profile.// The producer or auto-profile could have changed the profile.load_consumer(&consumer, profile, argc, argv);// See if producer has consumer already attachedif (!store && !consumer) {consumer = MLT_CONSUMER(mlt_service_consumer(MLT_PRODUCER_SERVICE(melt)));if (consumer) {// 增加引用计数mlt_properties_inc_ref(MLT_CONSUMER_PROPERTIES(consumer)); // because we explicitly close it// 设置传输回调函数mlt_properties_set_data(MLT_CONSUMER_PROPERTIES(consumer),"transport_callback",transport_action,0,NULL,NULL);}}// If we have no consumer, default to sdlif (store == NULL && consumer == NULL)consumer = create_consumer(profile, NULL);}// Set transport properties on consumer and produderif (consumer != NULL && melt != NULL) {mlt_properties_set_data(MLT_CONSUMER_PROPERTIES(consumer),"transport_producer",melt,0,NULL,NULL);mlt_properties_set_data(MLT_PRODUCER_PROPERTIES(melt),"transport_consumer",consumer,0,NULL,NULL);if (is_progress)mlt_properties_set_int(MLT_CONSUMER_PROPERTIES(consumer), "progress", is_progress);if (is_silent)mlt_properties_set_int(MLT_CONSUMER_PROPERTIES(consumer), "silent", is_silent);if (is_getc)mlt_properties_set_int(MLT_CONSUMER_PROPERTIES(consumer), "melt_getc", is_getc);}if (argc > 1 && melt != NULL && mlt_producer_get_length(melt) > 0) {// Parse the argumentsfor (i = 1; i < argc; i++) {if (!strcmp(argv[i], "-jack") && consumer) {setup_jack_transport(consumer, profile);} else if (!strcmp(argv[i], "-serialise")) {if (store != stdout)i++;} else {if (store != NULL)fprintf(store, "%s\n", argv[i]);i++;while (argv[i] != NULL && argv[i][0] != '-') {if (store != NULL)fprintf(store, "%s\n", argv[i]);i += 1;}i--;}}if (consumer != NULL && store == NULL) {// Get melt's propertiesmlt_properties melt_props = MLT_PRODUCER_PROPERTIES(melt);mlt_properties properties = MLT_CONSUMER_PROPERTIES(consumer);if (is_consumer_explicit) {// Apply group settingsmlt_properties group = mlt_properties_get_data(melt_props, "group", 0);// properties继承mlt_properties_inherit(properties, group);}int in = mlt_properties_get_int(properties, "in");int out = mlt_properties_get_int(properties, "out");if (in > 0 || out > 0) {if (out == 0) {out = mlt_producer_get_length(melt) - 1;}mlt_producer_set_in_and_out(melt, in, out);mlt_producer_seek(melt, 0);}// Connect consumer to meltmlt_consumer_connect(consumer, MLT_PRODUCER_SERVICE(melt));// Start the consumermlt_events_listen(properties,consumer,"consumer-fatal-error",(mlt_listener) on_fatal_error);if (mlt_consumer_start(consumer) == 0) {// Try to exit gracefully upon these signalssignal(SIGINT, stop_handler);signal(SIGTERM, stop_handler);
#ifndef _WIN32signal(SIGHUP, stop_handler);signal(SIGPIPE, stop_handler);
#endif// Transport functionalitytransport(melt, consumer);// Stop the consumermlt_consumer_stop(consumer);}} else if (store != NULL && store != stdout && name != NULL) {fprintf(stderr, "Project saved as %s.\n", name);fclose(store);}} else {show_usage(argv[0]);}// Disconnect producer from consumer to prevent ref cycles from closing servicesif (consumer) {error = mlt_properties_get_int(MLT_CONSUMER_PROPERTIES(consumer), "melt_error");mlt_consumer_connect(consumer, NULL);if (!is_abort)mlt_events_fire(MLT_CONSUMER_PROPERTIES(consumer),"consumer-cleanup",mlt_event_data_none());}if (is_abort)return error;// Close the producerif (melt != NULL)mlt_producer_close(melt);// Close the consumerif (consumer != NULL)mlt_consumer_close(consumer);// Close the factorymlt_profile_close(profile);mlt_profile_close(backup_profile);exit_factory:// Workaround qmelt on OS X from crashing at exit.
#if !defined(__MACH__) || !defined(QT_GUI_LIB)mlt_factory_close();
#endifreturn error;
}