【FFMPEG源码分析】通过ffmpeg截图命令分析ffmpeg.c源码流程
环境搭建
- Ubuntu 20.04
- 开启外设摄像头
- 截图命令:
ffmpeg -f video4linux2 -s 640x480 -i /dev/video0 -ss 0:0:2 -frames 1 /data/ffmpeg-4.2.7/exe_cmd/tmp/out2.jpg
参数解析
int main(int argc, char **argv)
{.................................;
#if CONFIG_AVDEVICEavdevice_register_all();
#endifavformat_network_init();show_banner(argc, argv, options);//1. 重点看下参数解析ffmpeg_parse_options(argc, argv);//2. 这里面进行具体的数据处理if (transcode() < 0)exit_program(1);}.................................;
}
int ffmpeg_parse_options(int argc, char **argv)
{OptionParseContext octx;uint8_t error[128];int ret;memset(&octx, 0, sizeof(octx));/* split the commandline into an internal representation */split_commandline(&octx, argc, argv, options, groups,FF_ARRAY_ELEMS(groups));/* apply global options */parse_optgroup(NULL, &octx.global_opts);/* configure terminal and setup signal handlers */term_init();/* open input files */open_files(&octx.groups[GROUP_INFILE], "input", open_input_file);init_complex_filters();/* open output files */open_files(&octx.groups[GROUP_OUTFILE], "output", open_output_file);.....................................;check_filter_outputs();.....................................;return ret;
}
split_commandline
//全局变量 设置给split_commandline
const OptionDef options[] = {/* main options */CMDUTILS_COMMON_OPTIONS{ "f", HAS_ARG | OPT_STRING | OPT_OFFSET |OPT_INPUT | OPT_OUTPUT, { .off = OFFSET(format) },"force format", "fmt" },{ "y", OPT_BOOL, { &file_overwrite },"overwrite output files" },...............................;
}enum OptGroup {GROUP_OUTFILE,GROUP_INFILE,
};//全局变量 设置给split_commandline
static const OptionGroupDef groups[] = {[GROUP_OUTFILE] = { "output url", NULL, OPT_OUTPUT },[GROUP_INFILE] = { "input url", "i", OPT_INPUT },
};int split_commandline(OptionParseContext *octx, int argc, char *argv[],const OptionDef *options,const OptionGroupDef *groups, int nb_groups)
{int optindex = 1;int dashdash = -2;//针对windows上输入参数字符集的转换如:utf-8等，不必深入。prepare_app_arguments(&argc, &argv);init_parse_context(octx, groups, nb_groups);av_log(NULL, AV_LOG_DEBUG, "Splitting the commandline.\\n");while (optindex < argc) {const char *opt = argv[optindex++], *arg;const OptionDef *po;int ret;if (opt[0] == '-' && opt[1] == '-' && !opt[2]) {dashdash = optindex;continue;}// -i之后的作为output的一个group，即全局变量groups中的GROUP_OUTFILEif (opt[0] != '-' || !opt[1] || dashdash+1 == optindex) {finish_group(octx, 0, opt);av_log(NULL, AV_LOG_DEBUG, " matched as %s.\\n", groups[0].name);continue;}opt++;#define GET_ARG(arg) \\
do { \\arg = argv[optindex++]; \\if (!arg) { \\av_log(NULL, AV_LOG_ERROR, "Missing argument for option '%s'.\\n", opt);\\return AVERROR(EINVAL); \\} \\
} while (0)//-i 以及-i 之前的参数全部存入全局变量groups中的GROUP_INFILE/* named group separators, e.g. -i */if ((ret = match_group_separator(groups, nb_groups, opt)) >= 0) {GET_ARG(arg);finish_group(octx, ret, arg);av_log(NULL, AV_LOG_DEBUG, " matched as %s with argument '%s'.\\n",groups[ret].name, arg);continue;}/* normal options */po = find_option(options, opt);if (po->name) {if (po->flags & OPT_EXIT) {/* optional argument, e.g. -h */arg = argv[optindex++];} else if (po->flags & HAS_ARG) {GET_ARG(arg);} else {arg = "1";}add_opt(octx, po, opt, arg);av_log(NULL, AV_LOG_DEBUG, " matched as option '%s' (%s) with ""argument '%s'.\\n", po->name, po->help, arg);continue;}/* AVOptions */if (argv[optindex]) {ret = opt_default(NULL, opt, argv[optindex]);if (ret >= 0) {av_log(NULL, AV_LOG_DEBUG, " matched as AVOption '%s' with ""argument '%s'.\\n", opt, argv[optindex]);optindex++;continue;} else if (ret != AVERROR_OPTION_NOT_FOUND) {av_log(NULL, AV_LOG_ERROR, "Error parsing option '%s' ""with argument '%s'.\\n", opt, argv[optindex]);return ret;}}/* boolean -nofoo options */if (opt[0] == 'n' && opt[1] == 'o' &&(po = find_option(options, opt + 2)) &&po->name && po->flags & OPT_BOOL) {add_opt(octx, po, opt, "0");av_log(NULL, AV_LOG_DEBUG, " matched as option '%s' (%s) with ""argument 0.\\n", po->name, po->help);continue;}av_log(NULL, AV_LOG_ERROR, "Unrecognized option '%s'.\\n", opt);return AVERROR_OPTION_NOT_FOUND;}if (octx->cur_group.nb_opts || codec_opts || format_opts || resample_opts)av_log(NULL, AV_LOG_WARNING, "Trailing options were found on the ""commandline.\\n");av_log(NULL, AV_LOG_DEBUG, "Finished splitting the commandline.\\n");return 0;
}
上述代码主要是将ffmpeg命令行参数解析到OptionParseContext中。OptionParseContext的成员变量OptionGroupList *groups由两个，一个为input OptionGroupList另一个为output OptionGroupList。一个OptionGroupList中由多个OptionGroup组成，而一个OptionGroup由多个Option组成。具体关系如下图:
OptionGroupList输入/输出参数以及option的遍历代码如下:
OptionParseContext octx;for(int i = 0; i < octx.nb_groups; i++) {OptionGroupList *ll = &octx.groups[i];av_log(NULL,AV_LOG_ERROR, "OptionGroupList[%d] def:%s\\n",i, ll->group_def->name);for(int j = 0; j < ll->nb_groups; j++) {OptionGroup *g = &ll->groups[j];av_log(NULL,AV_LOG_ERROR,"g[%d][%d],arg:%s, def: %s \\n",i,j, g->arg, g->group_def->name);for (int x = 0; x < g->nb_opts; x++) {Option *opt = &g->opts[x];av_log(NULL,AV_LOG_ERROR,"g[%d][%d], opts[%d],key:%s, value:%s, def: %s \\n",i,j,x, opt->key, opt->val, opt->opt->name);}}}
如命令行: ffmpeg -f video4linux2 -s 640x480 -i /dev/video0 -ss 0:0:2 -frames 1 /data/ffmpeg-4.2.7/exe_cmd/tmp/out2.jpg 解析后遍历结果如下:
OptionGroupList[0] def:output url
g[0][0],arg:/data/ffmpeg-4.2.7/exe_cmd/tmp/out2.jpg, def: output url
g[0][0], opts[0],key:ss, value:0:0:2, def: ss
g[0][0], opts[1],key:frames, value:1, def: frames
OptionGroupList[1] def:input url
g[1][0],arg:/dev/video0, def: input url
g[1][0], opts[0],key:f, value:video4linux2, def: f
g[1][0], opts[1],key:s, value:640x480, def: s
parse_optgroup
这个函数的作中是存储全局的option，如: -v debug 对所有模块都适用
int parse_optgroup(void *optctx, OptionGroup *g)
{int i, ret;for (i = 0; i < g->nb_opts; i++) {Option *o = &g->opts[i];ret = write_option(optctx, o->opt, o->key, o->val);if (ret < 0)return ret;}return 0;
}
open_files
参数解析完成之后，就是通过input url和output url找到对应的AVInputFormat和AVOutputFormat。
int ffmpeg_parse_options(int argc, char **argv) {................................................;//将input arg group传入进去open_files(&octx.groups[GROUP_INFILE], "input", open_input_file)................................................;
}static int open_files(OptionGroupList *l, const char *inout,int (*open_file)(OptionsContext*, const char*))
{int i, ret;for (i = 0; i < l->nb_groups; i++) {OptionGroup *g = &l->groups[i];OptionsContext o;init_options(&o);o.g = g;ret = parse_optgroup(&o, g);av_log(NULL, AV_LOG_DEBUG, "Opening an %s file: %s.\\n", inout, g->arg);//将input arg option group赋值到OptionsContext后调用open_input_fileret = open_file(&o, g->arg);uninit_options(&o);}return 0;
}
open_input_file
static int open_input_file(OptionsContext *o, const char *filename)
{InputFile *f;AVFormatContext *ic;AVInputFormat *file_iformat = NULL;int err, i, ret;int64_t timestamp;AVDictionary *unused_opts = NULL;AVDictionaryEntry *e = NULL;char * video_codec_name = NULL;char * audio_codec_name = NULL;char *subtitle_codec_name = NULL;char * data_codec_name = NULL;int scan_all_pmts_set = 0;.....................................;if (o->format) {//在本例中通过video4linux2 找到ff_v4l2_demuxerif (!(file_iformat = av_find_input_format(o->format))) {av_log(NULL, AV_LOG_FATAL, "Unknown input format: '%s'\\n", o->format);exit_program(1);}}............................;//分配AVFormatContextic = avformat_alloc_context();............................;av_log(NULL, AV_LOG_ERROR, "[yxy]use AVInputFormat:%s for file:%s \\n", file_iformat->name, filename);err = avformat_open_input(&ic, filename, file_iformat, &o->g->format_opts);/* apply forced codec ids */for (i = 0; i < ic->nb_streams; i++)choose_decoder(o, ic, ic->streams[i]);if (find_stream_info) {AVDictionary **opts = setup_find_stream_info_opts(ic, o->g->codec_opts);int orig_nb_streams = ic->nb_streams;ret = avformat_find_stream_info(ic, opts);}............................;/* update the current parameters so that they match the one of the input stream */add_input_streams(o, ic);/* dump the file content */av_dump_format(ic, nb_input_files, filename, 0);GROW_ARRAY(input_files, nb_input_files);f = av_mallocz(sizeof(*f));//存入全局变量input_filesinput_files[nb_input_files - 1] = f;f->ctx = ic;f->ist_index = nb_input_streams - ic->nb_streams;f->start_time = o->start_time;f->recording_time = o->recording_time;f->input_ts_offset = o->input_ts_offset;.......................................;return 0;
}
上面open_input的代码主要作用是通过input args options new一个AVFormatContext以及AVFormatContext.AVInputFormat 即ff_v4l2_demuxer， 并将AVFormatContext存入全局变量InputFile *input_files中。另外new出来了InputStream存放在全局变量InputStream **input_streams中。
open_output_file
static int open_output_file(OptionsContext *o, const char *filename)
{AVFormatContext *oc;int i, j, err;OutputFile *of;OutputStream *ost;InputStream *ist;AVDictionary *unused_opts = NULL;AVDictionaryEntry *e = NULL;int format_flags = 0;............................................;GROW_ARRAY(output_files, nb_output_files);of = av_mallocz(sizeof(*of));output_files[nb_output_files - 1] = of;of->ost_index = nb_output_streams;of->recording_time = o->recording_time;of->start_time = o->start_time;of->limit_filesize = o->limit_filesize;of->shortest = o->shortest;av_dict_copy(&of->opts, o->g->format_opts, 0);av_log(NULL, AV_LOG_ERROR, "[yxy]call avformat_alloc_output_context2 for file:%s \\n", filename);err = avformat_alloc_output_context2(&oc, NULL, o->format, filename);of->ctx = oc;if (o->recording_time != INT64_MAX)oc->duration = o->recording_time;oc->interrupt_callback = int_cb;e = av_dict_get(o->g->format_opts, "fflags", NULL, 0);if (e) {const AVOption *o = av_opt_find(oc, "fflags", NULL, 0, 0);av_opt_eval_flags(oc, o, e->value, &format_flags);}if (o->bitexact) {format_flags |= AVFMT_FLAG_BITEXACT;oc->flags |= AVFMT_FLAG_BITEXACT;}/* create streams for all unlabeled output pads */for (i = 0; i < nb_filtergraphs; i++) {FilterGraph *fg = filtergraphs[i];for (j = 0; j < fg->nb_outputs; j++) {OutputFilter *ofilter = fg->outputs[j];if (!ofilter->out_tmp || ofilter->out_tmp->name)continue;switch (ofilter->type) {case AVMEDIA_TYPE_VIDEO: o->video_disable = 1; break;case AVMEDIA_TYPE_AUDIO: o->audio_disable = 1; break;case AVMEDIA_TYPE_SUBTITLE: o->subtitle_disable = 1; break;}init_output_filter(ofilter, o, oc);}}if (!o->nb_stream_maps) {char *subtitle_codec_name = NULL;/* pick the "best" stream of each type *//* video: highest resolution */if (!o->video_disable && av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_VIDEO) != AV_CODEC_ID_NONE) {int area = 0, idx = -1;int qcr = avformat_query_codec(oc->oformat, oc->oformat->video_codec, 0);for (i = 0; i < nb_input_streams; i++) {int new_area;ist = input_streams[i];new_area = ist->st->codecpar->width * ist->st->codecpar->height + 100000000*!!ist->st->codec_info_nb_frames+ 5000000*!!(ist->st->disposition & AV_DISPOSITION_DEFAULT);if (ist->user_set_discard == AVDISCARD_ALL)continue;if((qcr!=MKTAG('A', 'P', 'I', 'C')) && (ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))new_area = 1;if (ist->st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO &&new_area > area) {if((qcr==MKTAG('A', 'P', 'I', 'C')) && !(ist->st->disposition & AV_DISPOSITION_ATTACHED_PIC))continue;area = new_area;idx = i;}}if (idx >= 0)new_video_stream(o, oc, idx);}/* audio: most channels */if (!o->audio_disable && av_guess_codec(oc->oformat, NULL, filename, NULL, AVMEDIA_TYPE_AUDIO) != AV_CODEC_ID_NONE) {int best_score = 0, idx = -1;for (i = 0; i < nb_input_streams; i++) {int score;ist = input_streams[i];score = ist->st->codecpar->channels + 100000000*!!ist->st->codec_info_nb_frames+ 5000000*!!(ist->st->disposition & AV_DISPOSITION_DEFAULT);if (ist->user_set_discard == AVDISCARD_ALL)continue;if (ist->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO &&score > best_score) {best_score = score;idx = i;}}if (idx >= 0)new_audio_stream(o, oc, idx);}/* subtitles: pick first */MATCH_PER_TYPE_OPT(codec_names, str, subtitle_codec_name, oc, "s");if (!o->subtitle_disable && (avcodec_find_encoder(oc->oformat->subtitle_codec) || subtitle_codec_name)) {for (i = 0; i < nb_input_streams; i++)if (input_streams[i]->st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE) {AVCodecDescriptor const *input_descriptor =avcodec_descriptor_get(input_streams[i]->st->codecpar->codec_id);AVCodecDescriptor const *output_descriptor = NULL;AVCodec const *output_codec =avcodec_find_encoder(oc->oformat->subtitle_codec);int input_props = 0, output_props = 0;if (input_streams[i]->user_set_discard == AVDISCARD_ALL)continue;if (output_codec)output_descriptor = avcodec_descriptor_get(output_codec->id);if (input_descriptor)input_props = input_descriptor->props & (AV_CODEC_PROP_TEXT_SUB | AV_CODEC_PROP_BITMAP_SUB);if (output_descriptor)output_props = output_descriptor->props & (AV_CODEC_PROP_TEXT_SUB | AV_CODEC_PROP_BITMAP_SUB);if (subtitle_codec_name ||input_props & output_props ||// Map dvb teletext which has neither property to any output subtitle encoderinput_descriptor && output_descriptor &&(!input_descriptor->props ||!output_descriptor->props)) {new_subtitle_stream(o, oc, i);break;}}}/* 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]->user_set_discard == AVDISCARD_ALL)continue;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);}}} else {for (i = 0; i < o->nb_stream_maps; i++) {StreamMap *map = &o->stream_maps[i];if (map->disabled)continue;if (map->linklabel) {FilterGraph *fg;OutputFilter *ofilter = NULL;int j, k;for (j = 0; j < nb_filtergraphs; j++) {fg = filtergraphs[j];for (k = 0; k < fg->nb_outputs; k++) {AVFilterInOut *out = fg->outputs[k]->out_tmp;if (out && !strcmp(out->name, map->linklabel)) {ofilter = fg->outputs[k];goto loop_end;}}}
loop_end:if (!ofilter) {av_log(NULL, AV_LOG_FATAL, "Output with label '%s' does not exist ""in any defined filter graph, or was already used elsewhere.\\n", map->linklabel);exit_program(1);}init_output_filter(ofilter, o, oc);} else {int src_idx = input_files[map->file_index]->ist_index + map->stream_index;ist = input_streams[input_files[map->file_index]->ist_index + map->stream_index];if (ist->user_set_discard == AVDISCARD_ALL) {av_log(NULL, AV_LOG_FATAL, "Stream #%d:%d is disabled and cannot be mapped.\\n",map->file_index, map->stream_index);exit_program(1);}if(o->subtitle_disable && ist->st->codecpar->codec_type == AVMEDIA_TYPE_SUBTITLE)continue;if(o-> audio_disable && ist->st->codecpar->codec_type == AVMEDIA_TYPE_AUDIO)continue;if(o-> video_disable && ist->st->codecpar->codec_type == AVMEDIA_TYPE_VIDEO)continue;if(o-> data_disable && ist->st->codecpar->codec_type == AVMEDIA_TYPE_DATA)continue;ost = NULL;switch (ist->st->codecpar->codec_type) {case AVMEDIA_TYPE_VIDEO: ost = new_video_stream (o, oc, src_idx); break;case AVMEDIA_TYPE_AUDIO: ost = new_audio_stream (o, oc, src_idx); break;case AVMEDIA_TYPE_SUBTITLE: ost = new_subtitle_stream (o, oc, src_idx); break;case AVMEDIA_TYPE_DATA: ost = new_data_stream (o, oc, src_idx); break;case AVMEDIA_TYPE_ATTACHMENT: ost = new_attachment_stream(o, oc, src_idx); break;case AVMEDIA_TYPE_UNKNOWN:if (copy_unknown_streams) {ost = new_unknown_stream (o, oc, src_idx);break;}default:av_log(NULL, ignore_unknown_streams ? AV_LOG_WARNING : AV_LOG_FATAL,"Cannot map stream #%d:%d - unsupported type.\\n",map->file_index, map->stream_index);if (!ignore_unknown_streams) {av_log(NULL, AV_LOG_FATAL,"If you want unsupported types ignored instead ""of failing, please use the -ignore_unknown option\\n""If you want them copied, please use -copy_unknown\\n");exit_program(1);}}if (ost)ost->sync_ist = input_streams[ input_files[map->sync_file_index]->ist_index+ map->sync_stream_index];}}}..............................;return 0;
}
上面代码主要是AVFormatContext以及AVFormatContext.AVFormatContext即ff_image2_muxer并将AVFormatContext存入全局变量 OutputFile **output_files中，以及new出来各个OutputStream存放在全局变量OutputStream **output_streams。
总结图
将args解析完成和open动作做完之后，所有的信息都放在了四个全局变量中，具体如下图:
transcode
static int transcode(void)
{int ret, i;AVFormatContext *os;OutputStream *ost;InputStream *ist;int64_t timer_start;int64_t total_packets_written = 0;//重点看下transcode_init 和transcode_stepret = transcode_init();.................................;while (!received_sigterm) {int64_t cur_time= av_gettime_relative();.................................;ret = transcode_step();if (ret < 0 && ret != AVERROR_EOF) {av_log(NULL, AV_LOG_ERROR, "Error while filtering: %s\\n", av_err2str(ret));break;}/* dump report by using the output first video and audio streams */print_report(0, timer_start, cur_time);}.................................;/* at the end of stream, we must flush the decoder buffers */for (i = 0; i < nb_input_streams; i++) {ist = input_streams[i];if (!input_files[ist->file_index]->eof_reached) {process_input_packet(ist, NULL, 0);}}flush_encoders();term_exit();..............;return ret;
}
transcode_init
static int transcode_init(void)
{int ret = 0, i, j, k;AVFormatContext *oc;OutputStream *ost;InputStream *ist;char error[1024] = {0};for (i = 0; i < nb_filtergraphs; i++) {FilterGraph *fg = filtergraphs[i];for (j = 0; j < fg->nb_outputs; j++) {OutputFilter *ofilter = fg->outputs[j];if (!ofilter->ost || ofilter->ost->source_index >= 0)continue;if (fg->nb_inputs != 1)continue;for (k = nb_input_streams-1; k >= 0 ; k--)if (fg->inputs[0]->ist == input_streams[k])break;ofilter->ost->source_index = k;}}/* init framerate emulation */for (i = 0; i < nb_input_files; i++) {InputFile *ifile = input_files[i];if (ifile->rate_emu)for (j = 0; j < ifile->nb_streams; j++)input_streams[j + ifile->ist_index]->start = av_gettime_relative();}/* init input streams, open decoder */for (i = 0; i < nb_input_streams; i++)if ((ret = init_input_stream(i, error, sizeof(error))) < 0) {for (i = 0; i < nb_output_streams; i++) {ost = output_streams[i];avcodec_close(ost->enc_ctx);}goto dump_format;}/* open each encoder */for (i = 0; i < nb_output_streams; i++) {// skip streams fed from filtergraphs until we have a frame for themif (output_streams[i]->filter)continue;ret = init_output_stream(output_streams[i], error, sizeof(error));if (ret < 0)goto dump_format;}/* discard unused programs */for (i = 0; i < nb_input_files; i++) {InputFile *ifile = input_files[i];for (j = 0; j < ifile->ctx->nb_programs; j++) {AVProgram *p = ifile->ctx->programs[j];int discard = AVDISCARD_ALL;for (k = 0; k < p->nb_stream_indexes; k++)if (!input_streams[ifile->ist_index + p->stream_index[k]]->discard) {discard = AVDISCARD_DEFAULT;break;}p->discard = discard;}}/* write headers for files with no streams */for (i = 0; i < nb_output_files; i++) {oc = output_files[i]->ctx;if (oc->oformat->flags & AVFMT_NOSTREAMS && oc->nb_streams == 0) {ret = check_init_output_file(output_files[i], i);if (ret < 0)goto dump_format;}}
....................................;
}
transcode_step
static int transcode_step(void)
{OutputStream *ost;InputStream *ist = NULL;int ret;ost = choose_output();....................;//处理output filtersif (ost->filter && !ost->filter->graph->graph) {if (ifilter_has_all_input_formats(ost->filter->graph)) {ret = configure_filtergraph(ost->filter->graph);if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Error reinitializing filters!\\n");return ret;}}}if (ost->filter && ost->filter->graph->graph) {if (!ost->initialized) {char error[1024] = {0};ret = init_output_stream(ost, error, sizeof(error));if (ret < 0) {av_log(NULL, AV_LOG_ERROR, "Error initializing output stream %d:%d -- %s\\n",ost->file_index, ost->index, error);exit_program(1);}}if ((ret = transcode_from_filter(ost->filter->graph, &ist)) < 0)return ret;if (!ist)return 0;} else if (ost->filter) {int i;for (i = 0; i < ost->filter->graph->nb_inputs; i++) {InputFilter *ifilter = ost->filter->graph->inputs[i];if (!ifilter->ist->got_output && !input_files[ifilter->ist->file_index]->eof_reached) {ist = ifilter->ist;break;}}if (!ist) {ost->inputs_done = 1;return 0;}} else {av_assert0(ost->source_index >= 0);ist = input_streams[ost->source_index];}//重点看下process_inputret = process_input(ist->file_index);if (ret == AVERROR(EAGAIN)) {if (input_files[ist->file_index]->eagain)ost->unavailable = 1;return 0;}if (ret < 0)return ret == AVERROR_EOF ? 0 : ret;//在这里面实现output处理return reap_filters(0);
}static int process_input(int file_index)
{InputFile *ifile = input_files[file_index];AVFormatContext *is;InputStream *ist;AVPacket pkt;int ret, thread_ret, i, j;int64_t duration;int64_t pkt_dts;is = ifile->ctx;//从demuxer中读取数据出来ret = get_input_packet(ifile, &pkt);..................;//如果需要decoder， decoder完之后写入filter context buffer， 有input filters则filters先处理process_input_packet(ist, &pkt, 0);discard_packet:av_packet_unref(&pkt);return 0;
}static int process_input_packet(InputStream *ist, const AVPacket *pkt, int no_eof)
{int ret = 0, i;int repeating = 0;int eof_reached = 0;AVPacket avpkt;if (!ist->saw_first_ts) {ist->dts = ist->st->avg_frame_rate.num ? - ist->dec_ctx->has_b_frames * AV_TIME_BASE / av_q2d(ist->st->avg_frame_rate) : 0;ist->pts = 0;if (pkt && pkt->pts != AV_NOPTS_VALUE && !ist->decoding_needed) {ist->dts += av_rescale_q(pkt->pts, ist->st->time_base, AV_TIME_BASE_Q);ist->pts = ist->dts; //unused but better to set it to a value thats not totally wrong}ist->saw_first_ts = 1;}if (ist->next_dts == AV_NOPTS_VALUE)ist->next_dts = ist->dts;if (ist->next_pts == AV_NOPTS_VALUE)ist->next_pts = ist->pts;if (!pkt) {/* EOF handling */av_init_packet(&avpkt);avpkt.data = NULL;avpkt.size = 0;} else {avpkt = *pkt;}if (pkt && pkt->dts != AV_NOPTS_VALUE) {ist->next_dts = ist->dts = av_rescale_q(pkt->dts, ist->st->time_base, AV_TIME_BASE_Q);if (ist->dec_ctx->codec_type != AVMEDIA_TYPE_VIDEO || !ist->decoding_needed)ist->next_pts = ist->pts = ist->dts;}// while we have more to decode or while the decoder did output something on EOFwhile (ist->decoding_needed) {int64_t duration_dts = 0;int64_t duration_pts = 0;int got_output = 0;int decode_failed = 0;ist->pts = ist->next_pts;ist->dts = ist->next_dts;switch (ist->dec_ctx->codec_type) {case AVMEDIA_TYPE_AUDIO:ret = decode_audio (ist, repeating ? NULL : &avpkt, &got_output,&decode_failed);break;case AVMEDIA_TYPE_VIDEO:ret = decode_video (ist, repeating ? NULL : &avpkt, &got_output, &duration_pts, !pkt,&decode_failed);..................;break;case AVMEDIA_TYPE_SUBTITLE:ret = transcode_subtitles(ist, &avpkt, &got_output, &decode_failed);...................;break;default:return -1;}}....................;return !eof_reached;
}static int decode_video(InputStream *ist, AVPacket *pkt, int *got_output, int64_t *duration_pts, int eof,int *decode_failed)
{AVFrame *decoded_frame;.................;ret = decode(ist->dec_ctx, decoded_frame, got_output, pkt ? &avpkt : NULL);...................;err = send_frame_to_filters(ist, decoded_frame);.................;return err < 0 ? err : ret;
}static int send_frame_to_filters(InputStream *ist, AVFrame *decoded_frame)
{int i, ret;AVFrame *f;..................;ret = ifilter_send_frame(ist->filters[i], f);return ret;
}static int ifilter_send_frame(InputFilter *ifilter, AVFrame *frame)
{FilterGraph *fg = ifilter->graph;......................;ret = av_buffersrc_add_frame_flags(ifilter->filter, frame, AV_BUFFERSRC_FLAG_PUSH);......................;return 0;
}
static int reap_filters(int flush)
{AVFrame *filtered_frame = NULL;int i;.......................;filtered_frame = ost->filtered_frame;while (1) {double float_pts = AV_NOPTS_VALUE; // this is identical to filtered_frame.pts but with higher precision//从filter input graph中读取filtered_frameret = av_buffersink_get_frame_flags(filter, filtered_frame,AV_BUFFERSINK_FLAG_NO_REQUEST);..................;switch (av_buffersink_get_type(filter)) {case AVMEDIA_TYPE_VIDEO:.......................;//重点看下video outdo_video_out(of, ost, filtered_frame, float_pts);break;case AVMEDIA_TYPE_AUDIO:.......................;do_audio_out(of, ost, filtered_frame);break;default: av_assert0(0);}av_frame_unref(filtered_frame);}}return 0;
}static void do_video_out(OutputFile *of,OutputStream *ost,AVFrame *next_picture,double sync_ipts)
{...........................;//将数据送入encoderret = avcodec_send_frame(enc, in_picture);// Make sure Closed Captions will not be duplicatedav_frame_remove_side_data(in_picture, AV_FRAME_DATA_A53_CC);while (1) {//从endcoder读取数据ret = avcodec_receive_packet(enc, &pkt);...................;frame_size = pkt.size;//将数据送到muxeroutput_packet(of, &pkt, ost, 0);}........................;}...........................;
}static void output_packet(OutputFile *of, AVPacket *pkt,OutputStream *ost, int eof)
{...........................;write_packet(of, pkt, ost, 0);...........................;
}static void write_packet(OutputFile *of, AVPacket *pkt, OutputStream *ost, int unqueue)
{AVFormatContext *s = of->ctx;AVStream *st = ost->st;.........................;ret = av_interleaved_write_frame(s, pkt);.........................;
}
// mux.c
int av_interleaved_write_frame(AVFormatContext *s, AVPacket *pkt)
{int ret, flush = 0;ret = prepare_input_packet(s, pkt);.........;for (;; ) {AVPacket opkt;int ret = interleave_packet(s, &opkt, pkt, flush);................;ret = write_packet(s, &opkt);} return ret;
}static int write_packet(AVFormatContext *s, AVPacket *pkt)
{int ret;int64_t pts_backup, dts_backup;......................;if ((pkt->flags & AV_PKT_FLAG_UNCODED_FRAME)) {AVFrame *frame = (AVFrame *)pkt->data;av_assert0(pkt->size == UNCODED_FRAME_PACKET_SIZE);ret = s->oformat->write_uncoded_frame(s, pkt->stream_index, &frame, 0);av_frame_free(&frame);} else {//向具体的muxer中写数据， 比如本例中为ff_image2_muxerret = s->oformat->write_packet(s, pkt);}............................;return ret;
}
总结
