【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_AVDEVICE
avdevice_register_all();
#endif
avformat_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_OUTFILE
if (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_file
ret = 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_demuxer
if (!(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AVFormatContext
ic = 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_files
input_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 encoder
input_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_step
ret = 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 them
if (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 filters
if (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_input
ret = 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 EOF
while (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_frame
ret = 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 out
do_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encoder
ret = avcodec_send_frame(enc, in_picture);
// Make sure Closed Captions will not be duplicated
av_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muxer
output_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_muxer
ret = s->oformat->write_packet(s, pkt);
}
............................;
return ret;
}
总结
