喀什网站建设,企业网址怎么制作,无网站可以做cpc吗,做网站推广需要多少费用demux模块
从前面一篇文章中可以得知#xff0c;demux模块的使用方法大致如下:
分配AVFormatContext通过avformat_open_input(…)传入AVFormatContext指针和文件路径#xff0c;启动demux通过av_read_frame(…) 从AVFormatContext中读取demux后的audio/video/subtitle数据包…demux模块
从前面一篇文章中可以得知demux模块的使用方法大致如下:
分配AVFormatContext通过avformat_open_input(…)传入AVFormatContext指针和文件路径启动demux通过av_read_frame(…) 从AVFormatContext中读取demux后的audio/video/subtitle数据包AVPacket
AVFormatContext *ic avformat_alloc_context();
avformat_open_input(ic, filename, null, null);
while(1) {AVPacket *pkt av_packet_alloc();av_read_frame(ic, pkt);..... use pkt data to do something.........;
}在阅读源码之前我们先提几个问题再顺着问题阅读源码:
AVFormatContext如何下载数据 ?如何匹配到具体的demuxer demuxer的模板是什么样的 如何新增一个demuxer ?demuxer是如何驱动起来的
下面我们分别看下avformat_alloc_context(…), avformat_open_input(…), av_read_frame(…)分别做了什么在文章结尾看看能否回答上面这几个问题。
avformat_alloc_context
ffmpeg\libavformat\option.c
AVFormatContext *avformat_alloc_context(void)
{FFFormatContext *const si av_mallocz(sizeof(*si));AVFormatContext *s;s si-pub;s-av_class av_format_context_class;s-io_open io_open_default;s-io_close ff_format_io_close_default;s-io_close2 io_close2_default;av_opt_set_defaults(s);si-pkt av_packet_alloc();si-parse_pkt av_packet_alloc();si-shortest_end AV_NOPTS_VALUE;return s;
}上面代码中比较重要的函数是io_open这个函数会创建AVIOContext数据下载模块。
int (*io_open)(struct AVFormatContext *s, AVIOContext **pb, const char *url,int flags, AVDictionary **options);avformat_open_input
ffmpeg\libavformat\demux.c
int avformat_open_input(AVFormatContext **ps, const char *filename,const AVInputFormat *fmt, AVDictionary **options)
{AVFormatContext *s *ps;FFFormatContext *si;AVDictionary *tmp NULL;ID3v2ExtraMeta *id3v2_extra_meta NULL;int ret 0;//如果外部没有传入AVFormatContext则在此分配if (!s !(s avformat_alloc_context()))return AVERROR(ENOMEM);FFFormatContext *si ffformatcontext(s);//如果外部有传入AVInputFormat则直接使用否则后面init_input中会进行分配if (fmt)s-iformat fmt;..........................................;//重点函数下面会深入细节进行分析if ((ret init_input(s, filename, tmp)) 0)goto fail;s-probe_score ret;.......................;//下面这一段代码比较关键AVInputFormat分配之后再来详细描述if (s-iformat-priv_data_size 0) {if (!(s-priv_data av_mallocz(s-iformat-priv_data_size))) {ret AVERROR(ENOMEM);goto fail;}if (s-iformat-priv_class) {*(const AVClass **) s-priv_data s-iformat-priv_class;av_opt_set_defaults(s-priv_data);if ((ret av_opt_set_dict(s-priv_data, tmp)) 0)goto fail;}}...........................;//关键函数用于下载第一笔数据和demux第一笔数据if (s-iformat-read_header)if ((ret s-iformat-read_header(s)) 0) {if (s-iformat-flags_internal FF_FMT_INIT_CLEANUP)goto close;goto fail;}}.......................;//更新codec信息后面会详细讲解update_stream_avctx(s);......................;return 0;
}通过上面代码可以梳理出有以下关键步骤:
init_input() 执行后会找到数据下载具体的模块AVIOContext和具体的demux模块AVInputFormat并进行初始化。分配AVInputFormat中的priv_data_size这个是指各各demux模块中私有的一个context结构图如: ts格式demuxer中的struct MpegTSContextmov格式demuxer中的struct MOVContext等AVInputFormat中的read_header() 会开始下载第一笔数据和demux第一笔数据update_stream_avctx(…) 获取并更新codec信息 下面深入分析下上面的四个步骤.
init_input
ffmpeg\libavformat\demux.c
static int init_input(AVFormatContext *s, const char *filename,AVDictionary **options)
{int ret;AVProbeData pd { filename, NULL, 0 };int score AVPROBE_SCORE_RETRY;//使用外部AVIOContext模块我们不关注这种caseif (s-pb) {........................;return 0;}//这一步因为score不够会获取iformat失败if ((s-iformat s-iformat-flags AVFMT_NOFILE) ||(!s-iformat (s-iformat av_probe_input_format2(pd, 0, score))))return score;//获取AVIOContext s-pbif ((ret s-io_open(s, s-pb, filename, AVIO_FLAG_READ | s-avio_flags, options)) 0)return ret;if (s-iformat)return 0;//在这里重新获取iformatreturn av_probe_input_buffer2(s-pb, s-iformat, filename,s, 0, s-format_probesize);
}下面来看下io_open和av_probe_input_buffer2的实现。 io_open赋值的位置:
ffmpeg\libavformat\option.c
AVFormatContext *avformat_alloc_context(void)
{FFFormatContext *const si av_mallocz(sizeof(*si));AVFormatContext *s;..............;s-io_open io_open_default;..............;
}再来看看io_open_default的具体实现
ffmpeg\libavformat\option.c
static int io_open_default(AVFormatContext *s, AVIOContext **pb,const char *url, int flags, AVDictionary **options)
{..............................;return ffio_open_whitelist(pb, url, flags, s-interrupt_callback, options, s-protocol_whitelist, s-protocol_blacklist);
}ffmpeg\libavformat\aviobuf.c
int ffio_open_whitelist(AVIOContext **s, const char *filename, int flags,const AVIOInterruptCB *int_cb, AVDictionary **options,const char *whitelist, const char *blacklist)
{URLContext *h;//获取到URLContextffurl_open_whitelist(h, filename, flags, int_cb, options, whitelist, blacklist, NULL);//获取到AVIOContext ffio_fdopen(s, h);return 0;
}ffmpeg\libavformat\avio.c
int ffurl_open_whitelist(URLContext **puc, const char *filename, int flags,const AVIOInterruptCB *int_cb, AVDictionary **options,const char *whitelist, const char* blacklist,URLContext *parent)
{AVDictionary *tmp_opts NULL;AVDictionaryEntry *e;ffurl_alloc(puc, filename, flags, int_cb);........set some options .......;ffurl_connect(*puc, options);.............;
}
// ffurl_alloc --------------- start ----------------------
ffmpeg\libavformat\avio.c
int ffurl_alloc(URLContext **puc, const char *filename, int flags,const AVIOInterruptCB *int_cb)
{const URLProtocol *p NULL;//通过url链接找到对应的下载数据的protocolp url_find_protocol(filename);if (p)return url_alloc_for_protocol(puc, p, filename, flags, int_cb);*puc NULL;return AVERROR_PROTOCOL_NOT_FOUND;
}ffmpeg\libavformat\avio.c
static const struct URLProtocol *url_find_protocol(const char *filename)
{const URLProtocol **protocols;char proto_str[128], proto_nested[128], *ptr;size_t proto_len strspn(filename, URL_SCHEME_CHARS);int i;//通过filename字符串找到proto_str即是什么协议if (filename[proto_len] ! : (strncmp(filename, subfile,, 8) || !strchr(filename proto_len 1, :)) ||is_dos_path(filename))strcpy(proto_str, file);elseav_strlcpy(proto_str, filename,FFMIN(proto_len 1, sizeof(proto_str)));av_strlcpy(proto_nested, proto_str, sizeof(proto_nested));if ((ptr strchr(proto_nested, )))*ptr \0;//获取到配置好的所有URLProtocol列表//ffmpeg通过config来配置支持哪些protocol编译之前config时会生成libavformat/protocol_list.c//里面会定义一个静态的全局数组url_protocols//static const URLProtocol * const url_protocols[] {// ff_http_protocol,// ff_https_protocol,// ff_tcp_protocol,// ff_tls_protocol,// NULL };protocols ffurl_get_protocols(NULL, NULL);if (!protocols)return NULL;for (i 0; protocols[i]; i) {const URLProtocol *up protocols[i];//通过URLProtocol的name字段与proto_str进行匹配//如: const URLProtocol ff_http_protocol {// .name http,// ........// }// const URLProtocol ff_tcp_protocol {// .name tcp,// ........// }if (!strcmp(proto_str, up-name)) {av_freep(protocols);return up;}if (up-flags URL_PROTOCOL_FLAG_NESTED_SCHEME !strcmp(proto_nested, up-name)) {av_freep(protocols);return up;}}av_freep(protocols);if (av_strstart(filename, https:, NULL) || av_strstart(filename, tls:, NULL))av_log(NULL, AV_LOG_WARNING, https protocol not found, recompile FFmpeg with openssl, gnutls or securetransport enabled.\n);return NULL;
}得到URLProtocol后再生成URLContext
static int url_alloc_for_protocol(URLContext **puc, const URLProtocol *up,const char *filename, int flags,const AVIOInterruptCB *int_cb)
{URLContext *uc;int err;...................;//分配URLContextuc av_mallocz(sizeof(URLContext) strlen(filename) 1);..................;uc-av_class ffurl_context_class;uc-filename (char *)uc[1];strcpy(uc-filename, filename);uc-prot up;uc-flags flags;uc-is_streamed 0; /* default not streamed */uc-max_packet_size 0; /* default: stream file */if (up-priv_data_size) {//分配网络协议模块自己的context结构体如struct TCPContextstruct HTTPContextuc-priv_data av_mallocz(up-priv_data_size);...................;if (up-priv_data_class) {char *start;*(const AVClass **)uc-priv_data up-priv_data_class;av_opt_set_defaults(uc-priv_data);..................;}}if (int_cb)uc-interrupt_callback *int_cb;*puc uc;return 0;
....................;
}
至此URLContext和URLProtocol都已经得到了。其关系为URLContext.prot为其对应的URLProtocol
// ffurl_alloc --------------- end ----------------------
得到URLContext后再看看ffurl_connect做了什么?
// ffurl_connect--------------- start ----------------------
int ffurl_connect(URLContext *uc, AVDictionary **options)
{..............................;//调用具体的protocol开始下载数据err uc-prot-url_open2 ? uc-prot-url_open2(uc,uc-filename,uc-flags,options) :uc-prot-url_open(uc, uc-filename, uc-flags);.......................;return 0;
}
// ffurl_connect--------------- end ----------------------
再来看看ffio_fdopen 如何分配AVIOContext
int ffio_fdopen(AVIOContext **s, URLContext *h)
{uint8_t *buffer NULL;buffer av_malloc(buffer_size);*s avio_alloc_context(buffer, buffer_size, h-flags AVIO_FLAG_WRITE, h,(int (*)(void *, uint8_t *, int)) ffurl_read,(int (*)(void *, uint8_t *, int)) ffurl_write,(int64_t (*)(void *, int64_t, int))ffurl_seek);(*s)-protocol_whitelist av_strdup(h-protocol_whitelist);(*s)-protocol_blacklist av_strdup(h-protocol_blacklist);if(h-prot) {(*s)-read_pause (int (*)(void *, int))h-prot-url_read_pause;(*s)-read_seek (int64_t (*)(void *, int, int64_t, int))h-prot-url_read_seek;if (h-prot-url_read_seek)(*s)-seekable | AVIO_SEEKABLE_TIME;}((FFIOContext*)(*s))-short_seek_get (int (*)(void *))ffurl_get_short_seek;(*s)-av_class ff_avio_class;return 0;
}io_open_default总结下其主要工作:
通过播放文件的链接获取到具体的协议如:http/https/tcp等然后在libavformat/protocol_list.c中定义一个静态的全局数组url_protocols遍历通过协议名称匹配到对应的URLProtocol分配生成URLContext并通过URLProtocol.priv_data_size分配具体协议的context如:struct TCPContextstruct HTTPContext,并将URLProtocol赋值给URLContext.proto字段。取URLContext得后调用ffurl_connect(…) 调用URLProtocol.url_open()进行初始化准备下载数据通过ffio_fdopen(…) 分配AVIOContext AVIOContext.opaque URLContext最终将AVIOContext赋值给AVFormatContext.pb 字段
下面再来看看av_probe_input_buffer2(…)函数如何找到具体的demux模块
int av_probe_input_buffer2(AVIOContext *pb, const AVInputFormat **fmt,const char *filename, void *logctx,unsigned int offset, unsigned int max_probe_size)
{AVProbeData pd { filename ? filename : };uint8_t *buf NULL;int ret 0, probe_size, buf_offset 0;int score 0;int ret2;//从AVIOContext 中获取mime_typeif (pb-av_class) {uint8_t *mime_type_opt NULL;char *semi;av_opt_get(pb, mime_type, AV_OPT_SEARCH_CHILDREN, mime_type_opt);pd.mime_type (const char *)mime_type_opt;semi pd.mime_type ? strchr(pd.mime_type, ;) : NULL;if (semi) {*semi \0;}}for (probe_size PROBE_BUF_MIN; probe_size max_probe_size !*fmt;probe_size FFMIN(probe_size 1,FFMAX(max_probe_size, probe_size 1))) {score probe_size max_probe_size ? AVPROBE_SCORE_RETRY : 0;/* Read probe data. */if ((ret av_reallocp(buf, probe_size AVPROBE_PADDING_SIZE)) 0)goto fail;//读取probe数据if ((ret avio_read(pb, buf buf_offset,probe_size - buf_offset)) 0) {.......................;}.................;/* Guess file format. */*fmt av_probe_input_format2(pd, 1, score);...................;}.....................;
}const AVInputFormat *av_probe_input_format2(const AVProbeData *pd,int is_opened, int *score_max)
{int score_ret;const AVInputFormat *fmt av_probe_input_format3(pd, is_opened, score_ret);if (score_ret *score_max) {*score_max score_ret;return fmt;} elsereturn NULL;
}const AVInputFormat *av_probe_input_format3(const AVProbeData *pd,int is_opened, int *score_ret)
{AVProbeData lpd *pd;const AVInputFormat *fmt1 NULL;const AVInputFormat *fmt NULL;int score, score_max 0;//通过从AVIOContext中读取的probe buffer来判断nodat值if (lpd.buf_size 10 ff_id3v2_match(lpd.buf, ID3v2_DEFAULT_MAGIC)) {if (lpd.buf_size id3len 16) {nodat ID3_ALMOST_GREATER_PROBE;} else if (id3len PROBE_BUF_MAX) {nodat ID3_GREATER_MAX_PROBE;} elsenodat ID3_GREATER_PROBE;}//遍历所有的demuxer获取得分最高的一个while ((fmt1 av_demuxer_iterate(i))) {score 0;if (fmt1-read_probe) {score fmt1-read_probe(lpd);if (score)av_log(NULL, AV_LOG_TRACE, Probing %s score:%d size:%d\n, fmt1-name, score, lpd.buf_size);if (fmt1-extensions av_match_ext(lpd.filename, fmt1-extensions)) {switch (nodat) {case NO_ID3:score FFMAX(score, 1);break;case ID3_GREATER_PROBE:case ID3_ALMOST_GREATER_PROBE:score FFMAX(score, AVPROBE_SCORE_EXTENSION / 2 - 1);break;case ID3_GREATER_MAX_PROBE:score FFMAX(score, AVPROBE_SCORE_EXTENSION);break;}}} else if (fmt1-extensions) {if (av_match_ext(lpd.filename, fmt1-extensions))score AVPROBE_SCORE_EXTENSION;}if (av_match_name(lpd.mime_type, fmt1-mime_type)) {score AVPROBE_SCORE_MIME;}}if (score score_max) {score_max score;fmt fmt1;} else if (score score_max)fmt NULL;}if (nodat ID3_GREATER_PROBE)score_max FFMIN(AVPROBE_SCORE_EXTENSION / 2 - 1, score_max);*score_ret score_max;return fmt;
}从上面的代码逻辑可以大致看出选取demuxer的逻辑:
通过ibavformat/demuxer_list.c中配置定义的全局数组demuxer_list,如
static const AVInputFormat * const demuxer_list[] {
ff_flac_demuxer,
ff_hls_demuxer,
ff_matroska_demuxer,
ff_mov_demuxer,
ff_mp3_demuxer,
ff_mpegts_demuxer,
ff_ogg_demuxer,
ff_wav_demuxer,
NULL };从AVIOContext中获取到数据的prop如: mime_type, 后缀名以及其他prop与每一个AVInputFormat进行匹配获取一个得分最高的AVInputFormat
AVFormatContext中的priv_data_size
再来重新看下avformat_open_input()中这段代码的含义 // s 为AVFormatContext, s-iformat为AVInputFormat类型if (s-iformat-priv_data_size 0) {if (!(s-priv_data av_mallocz(s-iformat-priv_data_size))) {ret AVERROR(ENOMEM);goto fail;}if (s-iformat-priv_class) {*(const AVClass **) s-priv_data s-iformat-priv_class;av_opt_set_defaults(s-priv_data);if ((ret av_opt_set_dict(s-priv_data, tmp)) 0)goto fail;}}以ff_mpegts_demuxer为例子s-iformat-priv_data_size为struct MpegTSContext因此av_mallocz(s-iformat-priv_data_size)实际分配了一个struct MpegTSContext。 *(const AVClass **) s-priv_data s-iformat-priv_class; 这句话的实际含义是MpegTSContext.class s-iformat-priv_class, 即为AVClass mpegts_class
从这里可以看出MpegTSContext 与AVInputFormat之间的关系AVInputFormat提供demuxer统一接口MpegTSContext为demuxer接口提供不同的操作上下文。
struct MpegTSContext {const AVClass *class; //这个成员必须是第一个/* user data */AVFormatContext *stream;/** raw packet size, including FEC if present */int raw_packet_size;...........;
};const AVInputFormat ff_mpegts_demuxer {.name mpegts,.long_name NULL_IF_CONFIG_SMALL(MPEG-TS (MPEG-2 Transport Stream)),.priv_data_size sizeof(MpegTSContext),.read_probe mpegts_probe,.read_header mpegts_read_header,.read_packet mpegts_read_packet,.read_close mpegts_read_close,.read_timestamp mpegts_get_dts,.flags AVFMT_SHOW_IDS | AVFMT_TS_DISCONT,.priv_class mpegts_class,
};static const AVClass mpegts_class {.class_name mpegts demuxer,.item_name av_default_item_name,.option options,.version LIBAVUTIL_VERSION_INT,
};AVInputFormat中的read_header
下面再来看看avformat_open_input(…)中的read_header干了什么?
if (s-iformat-read_header)//s 为AVFormatContext, s-iformat为AVInputFormatif ((ret s-iformat-read_header(s)) 0) {if (s-iformat-flags_internal FF_FMT_INIT_CLEANUP)goto close;goto fail;}const AVInputFormat ff_mpegts_demuxer {.name mpegts,.........................;.read_header mpegts_read_header,.read_packet mpegts_read_packet,..................;
};以ff_mpegts_demuxer为例子看看read_header具体做了什么?
static int mpegts_read_header(AVFormatContext *s)
{MpegTSContext *ts s-priv_data;AVIOContext *pb s-pb;.................;if (s-iformat ff_mpegts_demuxer) {seek_back(s, pb, pos);mpegts_open_section_filter(ts, SDT_PID, sdt_cb, ts, 1);mpegts_open_section_filter(ts, PAT_PID, pat_cb, ts, 1);mpegts_open_section_filter(ts, EIT_PID, eit_cb, ts, 1);handle_packets(ts, probesize / ts-raw_packet_size);/* if could not find service, enable auto_guess */ts-auto_guess 1;av_log(ts-stream, AV_LOG_TRACE, tuning done\n);s-ctx_flags | AVFMTCTX_NOHEADER;} else {.......................;}seek_back(s, pb, pos);return 0;
}具体再看下handle_packets函数
static int handle_packets(MpegTSContext *ts, int64_t nb_packets)
{AVFormatContext *s ts-stream;uint8_t packet[TS_PACKET_SIZE AV_INPUT_BUFFER_PADDING_SIZE];const uint8_t *data;int64_t packet_num;int ret 0;..............................;ts-stop_parse 0;packet_num 0;memset(packet TS_PACKET_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);for (;;) {packet_num;if (nb_packets ! 0 packet_num nb_packets ||ts-stop_parse 1) {ret AVERROR(EAGAIN);break;}if (ts-stop_parse 0)break;ret read_packet(s, packet, ts-raw_packet_size, data);if (ret ! 0)break;ret handle_packet(ts, data, avio_tell(s-pb));finished_reading_packet(s, ts-raw_packet_size);if (ret ! 0)break;}ts-last_pos avio_tell(s-pb);return ret;
}
主要看下read_packet 和 handle_packetc
static int read_packet(AVFormatContext *s, uint8_t *buf, int raw_packet_size,const uint8_t **data)
{*AVIOContext *pb s-pb*;int len;for (;;) {len ffio_read_indirect(pb, buf, TS_PACKET_SIZE, data);if (len ! TS_PACKET_SIZE)return len 0 ? len : AVERROR_EOF;/* check packet sync byte */if ((*data)[0] ! 0x47) {/* find a new packet start */if (mpegts_resync(s, raw_packet_size, *data) 0)return AVERROR(EAGAIN);elsecontinue;} else {break;}}return 0;
}
int ffio_read_indirect(AVIOContext *s, unsigned char *buf, int size, const unsigned char **data)
{if (s-buf_end - s-buf_ptr size !s-write_flag) {*data s-buf_ptr;s-buf_ptr size;return size;} else {*data buf;return avio_read(s, buf, size);}
}从上面的代码可以看出read_packet 是通过AVFormatContext.pb即AVIOContext 通过avio_read读取一个pkt。
handle_packet函数暂时还看不懂先放着后面再深入分析。
/* handle one TS packet */
static int handle_packet(MpegTSContext *ts, const uint8_t *packet, int64_t pos)
{MpegTSFilter *tss;int len, pid, cc, expected_cc, cc_ok, afc, is_start, is_discontinuity,has_adaptation, has_payload;const uint8_t *p, *p_end;pid AV_RB16(packet 1) 0x1fff;is_start packet[1] 0x40;tss ts-pids[pid];if (ts-auto_guess !tss is_start) {add_pes_stream(ts, pid, -1);tss ts-pids[pid];}if (!tss)return 0;if (is_start)tss-discard discard_pid(ts, pid);if (tss-discard)return 0;ts-current_pid pid;afc (packet[3] 4) 3;if (afc 0) /* reserved value */return 0;has_adaptation afc 2;has_payload afc 1;is_discontinuity has_adaptation packet[4] ! 0 /* with length 0 */(packet[5] 0x80); /* and discontinuity indicated *//* continuity check (currently not used) */cc (packet[3] 0xf);expected_cc has_payload ? (tss-last_cc 1) 0x0f : tss-last_cc;cc_ok pid 0x1FFF || // null packet PIDis_discontinuity ||tss-last_cc 0 ||expected_cc cc;tss-last_cc cc;if (!cc_ok) {av_log(ts-stream, AV_LOG_DEBUG,Continuity check failed for pid %d expected %d got %d\n,pid, expected_cc, cc);if (tss-type MPEGTS_PES) {PESContext *pc tss-u.pes_filter.opaque;pc-flags | AV_PKT_FLAG_CORRUPT;}}if (packet[1] 0x80) {av_log(ts-stream, AV_LOG_DEBUG, Packet had TEI flag set; marking as corrupt\n);if (tss-type MPEGTS_PES) {PESContext *pc tss-u.pes_filter.opaque;pc-flags | AV_PKT_FLAG_CORRUPT;}}p packet 4;if (has_adaptation) {int64_t pcr_h;int pcr_l;if (parse_pcr(pcr_h, pcr_l, packet) 0)tss-last_pcr pcr_h * 300 pcr_l;/* skip adaptation field */p p[0] 1;}/* if past the end of packet, ignore */p_end packet TS_PACKET_SIZE;if (p p_end || !has_payload)return 0;if (pos 0) {av_assert0(pos TS_PACKET_SIZE);ts-pos47_full pos - TS_PACKET_SIZE;}if (tss-type MPEGTS_SECTION) {if (is_start) {/* pointer field present */len *p;if (len p_end - p)return 0;if (len cc_ok) {/* write remaining section bytes */write_section_data(ts, tss,p, len, 0);/* check whether filter has been closed */if (!ts-pids[pid])return 0;}p len;if (p p_end) {write_section_data(ts, tss,p, p_end - p, 1);}} else {if (cc_ok) {write_section_data(ts, tss,p, p_end - p, 0);}}// stop find_stream_info from waiting for more streams// when all programs have received a PMTif (ts-stream-ctx_flags AVFMTCTX_NOHEADER ts-scan_all_pmts 0) {int i;for (i 0; i ts-nb_prg; i) {if (!ts-prg[i].pmt_found)break;}if (i ts-nb_prg ts-nb_prg 0) {int types 0;for (i 0; i ts-stream-nb_streams; i) {AVStream *st ts-stream-streams[i];if (st-codecpar-codec_type 0)types | 1st-codecpar-codec_type;}if ((types (1AVMEDIA_TYPE_AUDIO) types (1AVMEDIA_TYPE_VIDEO)) || pos 100000) {av_log(ts-stream, AV_LOG_DEBUG, All programs have pmt, headers found\n);ts-stream-ctx_flags ~AVFMTCTX_NOHEADER;}}}} else {int ret;// Note: The position here points actually behind the current packet.if (tss-type MPEGTS_PES) {if ((ret tss-u.pes_filter.pes_cb(tss, p, p_end - p, is_start,pos - ts-raw_packet_size)) 0)return ret;}}return 0;
}update_stream_avctx
static int update_stream_avctx(AVFormatContext *s)
{int ret;for (unsigned i 0; i s-nb_streams; i) {AVStream *const st s-streams[i];FFStream *const sti ffstream(st);.......................;ret avcodec_parameters_to_context(sti-avctx, st-codecpar);sti-need_context_update 0;}return 0;
}
//将AVStream中的codecpar信息赋值给FFStream中的AVCodecContext
int avcodec_parameters_to_context(AVCodecContext *codec,const AVCodecParameters *par)
{int ret;codec-codec_type par-codec_type;codec-codec_id par-codec_id;codec-codec_tag par-codec_tag;codec-bit_rate par-bit_rate;codec-bits_per_coded_sample par-bits_per_coded_sample;codec-bits_per_raw_sample par-bits_per_raw_sample;codec-profile par-profile;codec-level par-level;switch (par-codec_type) {case AVMEDIA_TYPE_VIDEO:codec-pix_fmt par-format;codec-width par-width;.............;break;case AVMEDIA_TYPE_AUDIO:codec-sample_fmt par-format;codec-sample_rate par-sample_rate;codec-block_align par-block_align;codec-frame_size par-frame_size;..............;break;case AVMEDIA_TYPE_SUBTITLE:codec-width par-width;codec-height par-height;break;}......................;return 0;
}av_read_frame
int av_read_frame(AVFormatContext *s, AVPacket *pkt)
{FFFormatContext *const si ffformatcontext(s);const int genpts s-flags AVFMT_FLAG_GENPTS;int eof 0;int ret;AVStream *st;.........................;for (;;) {.....................;read_frame_internal(s, pkt);.....................;}........................;return ret;
}
static int read_frame_internal(AVFormatContext *s, AVPacket *pkt)
{FFFormatContext *const si ffformatcontext(s);int ret, got_packet 0;AVDictionary *metadata NULL;while (!got_packet !si-parse_queue.head) {AVStream *st;FFStream *sti;/* read next packet */ret ff_read_packet(s, pkt);..............................;}return ret;
}int ff_read_packet(AVFormatContext *s, AVPacket *pkt)
{FFFormatContext *const si ffformatcontext(s);int err;for (;;) {PacketListEntry *pktl si-raw_packet_buffer.head;AVStream *st;FFStream *sti;const AVPacket *pkt1;...................;err s-iformat-read_packet(s, pkt);......................;}......................;
}
以MpegTSContext为例子,看看pkt是如何存储如何被读出来的c
static int mpegts_read_packet(AVFormatContext *s, AVPacket *pkt)
{MpegTSContext *ts s-priv_data;int ret, i;pkt-size -1;ts-pkt pkt;//这个函数中会做具体的demux动作ret handle_packets(ts, 0);..........................;return ret;
}
static int handle_packets(MpegTSContext *ts, int64_t nb_packets)
{AVFormatContext *s ts-stream;uint8_t packet[TS_PACKET_SIZE AV_INPUT_BUFFER_PADDING_SIZE];const uint8_t *data;int64_t packet_num;int ret 0;..........................;ts-stop_parse 0;packet_num 0;memset(packet TS_PACKET_SIZE, 0, AV_INPUT_BUFFER_PADDING_SIZE);for (;;) {packet_num;if (nb_packets ! 0 packet_num nb_packets ||ts-stop_parse 1) {ret AVERROR(EAGAIN);break;}if (ts-stop_parse 0)break;//从网络io中读取未demux的数据存储在data变量中ret read_packet(s, packet, ts-raw_packet_size, data);if (ret ! 0)break;//在此函数中将data中的数据demux之后存放至MpegTSContext.pktret handle_packet(ts, data, avio_tell(s-pb));finished_reading_packet(s, ts-raw_packet_size);if (ret ! 0)break;}ts-last_pos avio_tell(s-pb);return ret;
}问题解答 AVFormatContext如何下载数据 ? 下图中蓝色线路图表示数据下载过程即通过AVIOContext下载。 如何匹配到具体的demuxer 读取media数据开头一段数据遍历libavformat/demuxer_list.c中配置定义的全局数组demuxer_list将此数据通过每一个demuer的read_probe(…)解析匹配得到一个socre或者通过mime_type和文件后缀名得到socre 取socre最高的一个作为当前数据的demuxer模块。 demuxer的模板是什么样的 如何新增一个demuxer ? 在libavformat/demuxer_list.c中增加一个ff_yxyts_demuxer 如:
static const AVInputFormat * const demuxer_list[] {
ff_flac_demuxer,
ff_hls_demuxer,
ff_yxyts_demuxer,
NULL };
struct YxyTSContext {const AVClass *class; //这个成员必须是第一个/* user data */AVFormatContext *stream;/** raw packet size, including FEC if present */int raw_packet_size;...........;
};
const AVInputFormat ff_yxyts_demuxer {.name mpegts,.long_name NULL_IF_CONFIG_SMALL(MPEG-TS (MPEG-2 Transport Stream)),.priv_data_size sizeof(YxyTSContext),.read_probe yxyts_probe,.read_header yxyts_read_header,.read_packet yxyts_read_packet,.read_close yxyts_read_close,.read_timestamp yxyts_get_dts,.flags AVFMT_SHOW_IDS | AVFMT_TS_DISCONT,.priv_class yxyts_class,
};demuxer是如何驱动起来的 从下图中可以看出需要上层应用主动调用av_read_frame(…)获取源数据并demux然后将demux出来的audio/video的info信息存入AVStream中具体的audio/video数据通过AVPacket返回给上层应用。
