ffmpeg框架阅读笔记一:读取数据帧函数 int av_read_frame(AVFormatContext *s, AVPacket *pkt)

做音频播放，数据源从完整音频文件变成了网络拉取音频流到缓冲区，实现片段流的播放。分析av_read_frame过程，自定义获取数据源的功能。重点查找如何读入数据源。

首先分析函数av_read_frame。

[cpp] view plain copy
int av_read_frame(AVFormatContext *s, AVPacket *pkt)
{
//包含AVPacket结构体的链表结点
AVPacketList *pktl;
int eof=0;
const int genpts= s->flags & AVFMT_FLAG_GENPTS;

for(;;){  
    pktl = s->packet_buffer;  
    if (pktl) {  
        AVPacket *next_pkt= &pktl->pkt;  

        if(genpts && next_pkt->dts != AV_NOPTS_VALUE){  
            int wrap_bits = s->streams[next_pkt->stream_index]->pts_wrap_bits;  
            while(pktl && next_pkt->pts == AV_NOPTS_VALUE){  
                if(   pktl->pkt.stream_index == next_pkt->stream_index  
                   && (0 > av_compare_mod(next_pkt->dts, pktl->pkt.dts, 2LL << (wrap_bits - 1)))  
                   && av_compare_mod(pktl->pkt.pts, pktl->pkt.dts, 2LL << (wrap_bits - 1))) { //not b frame  
                    next_pkt->pts= pktl->pkt.dts;  
                }  
                pktl= pktl->next;  
            }  
            pktl = s->packet_buffer;  
        }  

        if(   next_pkt->pts != AV_NOPTS_VALUE  
           || next_pkt->dts == AV_NOPTS_VALUE  
           || !genpts || eof){  
            /* read packet from packet buffer, if there is data */  
            *pkt = *next_pkt;  
            s->packet_buffer = pktl->next;  
            av_free(pktl);  
            return 0;  
        }  
    }  

    if(genpts){  
        //这里读取数据   
        int ret= av_read_frame_internal(s, pkt);  
        if(ret<0){  
            if(pktl && ret != AVERROR(EAGAIN)){  
                eof=1;  
                continue;  
            }else  
                return ret;  
        }  

        if(av_dup_packet(add_to_pktbuf(&s->packet_buffer, pkt,  
                                       &s->packet_buffer_end)) < 0)  
            return AVERROR(ENOMEM);  
    }else{  
        assert(!s->packet_buffer);  
        return av_read_frame_internal(s, pkt);  
    }  
}  

}
上面代码找到av_read_frame_internal函数。其他代码不加分析。看的也不是很懂。接下来是av_read_frame_internal。

[cpp] view plain copy
static int av_read_frame_internal(AVFormatContext *s, AVPacket *pkt)
{
AVStream *st;
int len, ret, i;
//初始化pkt的各个成员
av_init_packet(pkt);

for(;;) {  
    /* select current input stream component */  
    //获得当前输入流  
    st = s->cur_st;  
    if (st) {  
        if (!st->need_parsing || !st->parser) {  
            /* no parsing needed: we just output the packet as is */  
            /* raw data support */  
            *pkt = st->cur_pkt;  
            st->cur_pkt.data= NULL;  
            st->cur_pkt.side_data_elems = 0;  
            st->cur_pkt.side_data = NULL;  
            compute_pkt_fields(s, st, NULL, pkt);  
            s->cur_st = NULL;  
            if ((s->iformat->flags & AVFMT_GENERIC_INDEX) &&  
                (pkt->flags & AV_PKT_FLAG_KEY) && pkt->dts != AV_NOPTS_VALUE) {  
                ff_reduce_index(s, st->index);  
                av_add_index_entry(st, pkt->pos, pkt->dts, 0, 0, AVINDEX_KEYFRAME);  
            }  
            break;  
        } else if (st->cur_len > 0 && st->discard < AVDISCARD_ALL) {  
            len = av_parser_parse2(st->parser, st->codec, &pkt->data, &pkt->size,  
                                   st->cur_ptr, st->cur_len,  
                                   st->cur_pkt.pts, st->cur_pkt.dts,  
                                   st->cur_pkt.pos);  
            st->cur_pkt.pts = AV_NOPTS_VALUE;  
            st->cur_pkt.dts = AV_NOPTS_VALUE;  
            /* increment read pointer */  
            st->cur_ptr += len;  
            st->cur_len -= len;  

            /* return packet if any */  
            if (pkt->size) {  
            got_packet:  
                pkt->duration = 0;  
                pkt->stream_index = st->index;  
                pkt->pts = st->parser->pts;  
                pkt->dts = st->parser->dts;  
                pkt->pos = st->parser->pos;  
                if(pkt->data == st->cur_pkt.data && pkt->size == st->cur_pkt.size){  
                    s->cur_st = NULL;  
                    pkt->destruct= st->cur_pkt.destruct;  
                    st->cur_pkt.destruct= NULL;  
                    st->cur_pkt.data    = NULL;  
                    assert(st->cur_len == 0);  
                }else{  
                pkt->destruct = NULL;  
                }  
                compute_pkt_fields(s, st, st->parser, pkt);  

                if((s->iformat->flags & AVFMT_GENERIC_INDEX) && pkt->flags & AV_PKT_FLAG_KEY){  
                    int64_t pos= (st->parser->flags & PARSER_FLAG_COMPLETE_FRAMES) ? pkt->pos : st->parser->frame_offset;  
                    ff_reduce_index(s, st->index);  
                    av_add_index_entry(st, pos, pkt->dts,  
                                       0, 0, AVINDEX_KEYFRAME);  
                }  

                break;  
            }  
        } else {  
            /* free packet */  
            av_free_packet(&st->cur_pkt);  
            s->cur_st = NULL;  
        }  
    } else { //当前输入流内容不存在 去数据源读取  
        AVPacket cur_pkt;  
        /* read next packet */  
        //读下一个数据包  
        ret = av_read_packet(s, &cur_pkt);  
        if (ret < 0) {  
            if (ret == AVERROR(EAGAIN))  
                return ret;  
            /* return the last frames, if any */  
            for(i = 0; i < s->nb_streams; i++) {  
                st = s->streams[i];  
                if (st->parser && st->need_parsing) {  
                    av_parser_parse2(st->parser, st->codec,  
                                    &pkt->data, &pkt->size,  
                                    NULL, 0,  
                                    AV_NOPTS_VALUE, AV_NOPTS_VALUE,  
                                    AV_NOPTS_VALUE);  
                    if (pkt->size)  
                        goto got_packet;  
                }  
            }  
            /* no more packets: really terminate parsing */  
            return ret;  
        }  
        st = s->streams[cur_pkt.stream_index];  
        st->cur_pkt= cur_pkt;  

        if(st->cur_pkt.pts != AV_NOPTS_VALUE &&  
           st->cur_pkt.dts != AV_NOPTS_VALUE &&  
           st->cur_pkt.pts < st->cur_pkt.dts){  
            av_log(s, AV_LOG_WARNING, "Invalid timestamps stream=%d, pts=%"PRId64", dts=%"PRId64", size=%d\n",  
                st->cur_pkt.stream_index,  
                st->cur_pkt.pts,  
                st->cur_pkt.dts,  
                st->cur_pkt.size);  

// av_free_packet(&st->cur_pkt);
// return -1;
}

        if(s->debug & FF_FDEBUG_TS)  
            av_log(s, AV_LOG_DEBUG, "av_read_packet stream=%d, pts=%"PRId64", dts=%"PRId64", size=%d, duration=%d, flags=%d\n",  
                st->cur_pkt.stream_index,  
                st->cur_pkt.pts,  
                st->cur_pkt.dts,  
                st->cur_pkt.size,  
                st->cur_pkt.duration,  
                st->cur_pkt.flags);  

        s->cur_st = st;  
        st->cur_ptr = st->cur_pkt.data;  
        st->cur_len = st->cur_pkt.size;  
        if (st->need_parsing && !st->parser && !(s->flags & AVFMT_FLAG_NOPARSE)) {  
            st->parser = av_parser_init(st->codec->codec_id);  
            if (!st->parser) {  
                /* no parser available: just output the raw packets */  
                st->need_parsing = AVSTREAM_PARSE_NONE;  
            }else if(st->need_parsing == AVSTREAM_PARSE_HEADERS){  
                st->parser->flags |= PARSER_FLAG_COMPLETE_FRAMES;  
            }else if(st->need_parsing == AVSTREAM_PARSE_FULL_ONCE){  
                st->parser->flags |= PARSER_FLAG_ONCE;  
            }  
        }  
    }  
}  
if(s->debug & FF_FDEBUG_TS)  
    av_log(s, AV_LOG_DEBUG, "av_read_frame_internal stream=%d, pts=%"PRId64", dts=%"PRId64", size=%d, duration=%d, flags=%d\n",  
        pkt->stream_index,  
        pkt->pts,  
        pkt->dts,  
        pkt->size,  
        pkt->duration,  
        pkt->flags);  

return 0;  

}

找到函数int av_read_packet(AVFormatContext *s, AVPacket *pkt)
[cpp] view plain copy
int av_read_packet(AVFormatContext *s, AVPacket *pkt)
{
int ret, i;
AVStream *st;

for(;;){  
    AVPacketList *pktl = s->raw_packet_buffer;  
   //格式上下文存在原生的包数据  
    if (pktl) {  
        *pkt = pktl->pkt;  
        if(s->streams[pkt->stream_index]->request_probe <= 0){  
            s->raw_packet_buffer = pktl->next;  
            s->raw_packet_buffer_remaining_size += pkt->size;  
            av_free(pktl);  
            return 0;  
        }  
    }  

    av_init_packet(pkt);  
    //原生包数据不存在 通过AVInputFormat的read_packet函数指针成员来调用函数获取数据源  
    //AVInputFormat是不同格式数据的操作函数集合。在注册函数中初始化所有格式的该结构体变量。  
    ret= s->iformat->read_packet(s, pkt);  
    if (ret < 0) {  
        if (!pktl || ret == AVERROR(EAGAIN))  
            return ret;  
        for (i = 0; i < s->nb_streams; i++)  
            if(s->streams[i]->request_probe > 0)  
                s->streams[i]->request_probe = -1;  
        continue;  
    }  

    if(!(s->flags & AVFMT_FLAG_KEEP_SIDE_DATA))  
        av_packet_merge_side_data(pkt);  
    st= s->streams[pkt->stream_index];  

    switch(st->codec->codec_type){  
    case AVMEDIA_TYPE_VIDEO:  
        if(s->video_codec_id)   st->codec->codec_id= s->video_codec_id;  
        break;  
    case AVMEDIA_TYPE_AUDIO:  
        if(s->audio_codec_id)   st->codec->codec_id= s->audio_codec_id;  
        break;  
    case AVMEDIA_TYPE_SUBTITLE:  
        if(s->subtitle_codec_id)st->codec->codec_id= s->subtitle_codec_id;  
        break;  
    }  

    if(!pktl && st->request_probe <= 0)  
        return ret;  

    add_to_pktbuf(&s->raw_packet_buffer, pkt, &s->raw_packet_buffer_end);  
    s->raw_packet_buffer_remaining_size -= pkt->size;  

    if(st->request_probe>0){  
        AVProbeData *pd = &st->probe_data;  
        int end;  
        av_log(s, AV_LOG_DEBUG, "probing stream %d pp:%d\n", st->index, st->probe_packets);  
        --st->probe_packets;  

        pd->buf = av_realloc(pd->buf, pd->buf_size+pkt->size+AVPROBE_PADDING_SIZE);  
        memcpy(pd->buf+pd->buf_size, pkt->data, pkt->size);  
        pd->buf_size += pkt->size;  
        memset(pd->buf+pd->buf_size, 0, AVPROBE_PADDING_SIZE);  

        end=    s->raw_packet_buffer_remaining_size <= 0  
             || st->probe_packets<=0;  

        if(end || av_log2(pd->buf_size) != av_log2(pd->buf_size - pkt->size)){  
            int score= set_codec_from_probe_data(s, st, pd);  
            if(    (st->codec->codec_id != CODEC_ID_NONE && score > AVPROBE_SCORE_MAX/4)  
                || end){  
                pd->buf_size=0;  
                av_freep(&pd->buf);  
                st->request_probe= -1;  
                if(st->codec->codec_id != CODEC_ID_NONE){  
                av_log(s, AV_LOG_DEBUG, "probed stream %d\n", st->index);  
                }else  
                    av_log(s, AV_LOG_WARNING, "probed stream %d failed\n", st->index);  
            }  
        }  
    }  
}  

}

分析AVInpuFormat结构体初始化过程
[cpp] view plain copy
AVInputFormat ff_flv_demuxer = {
“flv”,
NULL_IF_CONFIG_SMALL(“FLV format”),
sizeof(FLVContext),
flv_probe,
flv_read_header,
//读数据包的函数指针
flv_read_packet,
.read_seek = flv_read_seek,

if 0

.read_seek2 = flv_read_seek2,  

endif

.extensions = "flv",  
.value = CODEC_ID_FLV1,  

};

分析flv_read_packet
[cpp] view plain copy
static int flv_read_packet(AVFormatContext *s, AVPacket *pkt)
{
FLVContext *flv = s->priv_data;
int ret, i, type, size, flags, is_audio;
int64_t next, pos;
int64_t dts, pts = AV_NOPTS_VALUE;
AVStream *st = NULL;

for(;;avio_skip(s->pb, 4)){ /* pkt size is repeated at end. skip it */
pos = avio_tell(s->pb);
type = avio_r8(s->pb);
size = avio_rb24(s->pb);
dts = avio_rb24(s->pb);
dts |= avio_r8(s->pb) << 24;
av_dlog(s, “type:%d, size:%d, dts:%”PRId64”\n”, type, size, dts);
if (url_feof(s->pb))
return AVERROR_EOF;
avio_skip(s->pb, 3); /* stream id, always 0 */
flags = 0;

if(size == 0)  
    continue;  

next= size + avio_tell(s->pb);  

if (type == FLV_TAG_TYPE_AUDIO) {  
    is_audio=1;  
    flags = avio_r8(s->pb);  
    size--;  
} else if (type == FLV_TAG_TYPE_VIDEO) {  
    is_audio=0;  
    flags = avio_r8(s->pb);  
    size--;  
    if ((flags & 0xf0) == 0x50) /* video info / command frame */  
        goto skip;  
} else {  
    if (type == FLV_TAG_TYPE_META && size > 13+1+4)  
        flv_read_metabody(s, next);  
    else /* skip packet */  
        av_log(s, AV_LOG_DEBUG, "skipping flv packet: type %d, size %d, flags %d\n", type, size, flags);  
skip:  
    avio_seek(s->pb, next, SEEK_SET);  
    continue;  
}  

/* skip empty data packets */  
if (!size)  
    continue;  

/* now find stream */  
for(i=0;inb_streams;i++) {  
    st = s->streams[i];  
    if (st->id == is_audio)  
        break;  
}  
if(i == s->nb_streams){  
    av_log(s, AV_LOG_ERROR, "invalid stream\n");  
    st= create_stream(s, is_audio);  
    s->ctx_flags &= ~AVFMTCTX_NOHEADER;  
}  
av_dlog(s, "%d %X %d \n", is_audio, flags, st->discard);  
if(  (st->discard >= AVDISCARD_NONKEY && !((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_KEY ||         is_audio))  
   ||(st->discard >= AVDISCARD_BIDIR  &&  ((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_DISP_INTER && !is_audio))  
   || st->discard >= AVDISCARD_ALL  
   ){  
    avio_seek(s->pb, next, SEEK_SET);  
    continue;  
}  
if ((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_KEY)  
    av_add_index_entry(st, pos, dts, size, 0, AVINDEX_KEYFRAME);  
break;  

}

// if not streamed and no duration from metadata then seek to end to find the duration from the timestamps  
if(s->pb->seekable && (!s->duration || s->duration==AV_NOPTS_VALUE)){  
    int size;  
    const int64_t pos= avio_tell(s->pb);  
    const int64_t fsize= avio_size(s->pb);  
    avio_seek(s->pb, fsize-4, SEEK_SET);  
    size= avio_rb32(s->pb);  
    avio_seek(s->pb, fsize-3-size, SEEK_SET);  
    if(size == avio_rb24(s->pb) + 11){  
        uint32_t ts = avio_rb24(s->pb);  
        ts |= avio_r8(s->pb) << 24;  
        s->duration = ts * (int64_t)AV_TIME_BASE / 1000;  
    }  
    avio_seek(s->pb, pos, SEEK_SET);  
}  

if(is_audio){  
    if(!st->codec->channels || !st->codec->sample_rate || !st->codec->bits_per_coded_sample) {  
        st->codec->channels = (flags & FLV_AUDIO_CHANNEL_MASK) == FLV_STEREO ? 2 : 1;  
        st->codec->sample_rate = (44100 << ((flags & FLV_AUDIO_SAMPLERATE_MASK) >> FLV_AUDIO_SAMPLERATE_OFFSET) >> 3);  
        st->codec->bits_per_coded_sample = (flags & FLV_AUDIO_SAMPLESIZE_MASK) ? 16 : 8;  
    }  
    if(!st->codec->codec_id){  
        flv_set_audio_codec(s, st, flags & FLV_AUDIO_CODECID_MASK);  
    }  
}else{  
    size -= flv_set_video_codec(s, st, flags & FLV_VIDEO_CODECID_MASK);  
}  

if (st->codec->codec_id == CODEC_ID_AAC ||  
    st->codec->codec_id == CODEC_ID_H264) {  
    int type = avio_r8(s->pb);  
    size--;  
    if (st->codec->codec_id == CODEC_ID_H264) {  
        int32_t cts = (avio_rb24(s->pb)+0xff800000)^0xff800000; // sign extension  
        pts = dts + cts;  
        if (cts < 0) { // dts are wrong  
            flv->wrong_dts = 1;  
            av_log(s, AV_LOG_WARNING, "negative cts, previous timestamps might be wrong\n");  
        }  
        if (flv->wrong_dts)  
            dts = AV_NOPTS_VALUE;  
    }  
    if (type == 0) {  
        if ((ret = flv_get_extradata(s, st, size)) < 0)  
            return ret;  
        if (st->codec->codec_id == CODEC_ID_AAC) {  
            MPEG4AudioConfig cfg;  
            ff_mpeg4audio_get_config(&cfg, st->codec->extradata,  
                                     st->codec->extradata_size);  
            st->codec->channels = cfg.channels;  
            if (cfg.ext_sample_rate)  
                st->codec->sample_rate = cfg.ext_sample_rate;  
            else  
                st->codec->sample_rate = cfg.sample_rate;  
            av_dlog(s, "mp4a config channels %d sample rate %d\n",  
                    st->codec->channels, st->codec->sample_rate);  
        }  

        ret = AVERROR(EAGAIN);  
        goto leave;  
    }  
}  

/* skip empty data packets */  
if (!size) {  
    ret = AVERROR(EAGAIN);  
    goto leave;  
}  

//从AVIOContext读取数据
ret= av_get_packet(s->pb, pkt, size);
if (ret < 0) {
return AVERROR(EIO);
}
/* note: we need to modify the packet size here to handle the last
packet */
pkt->size = ret;
pkt->dts = dts;
pkt->pts = pts == AV_NOPTS_VALUE ? dts : pts;
pkt->stream_index = st->index;

if (is_audio || ((flags & FLV_VIDEO_FRAMETYPE_MASK) == FLV_FRAME_KEY))  
    pkt->flags |= AV_PKT_FLAG_KEY;  

leave:
avio_skip(s->pb, 4);
return ret;
}

分析av_get_packet()
[cpp] view plain copy
int av_get_packet(AVIOContext *s, AVPacket *pkt, int size)
{
//pkt分配空间并初始化
int ret= av_new_packet(pkt, size);

if(ret<0)  
    return ret;  

pkt->pos= avio_tell(s);  

//从io上下文读取数据  
ret= avio_read(s, pkt->data, size);  
if(ret<=0)  
    av_free_packet(pkt);  
else  
    av_shrink_packet(pkt, ret);  

return ret;  

}

分析avio_read
[cpp] view plain copy
int avio_read(AVIOContext *s, unsigned char *buf, int size)
{
int len, size1;

size1 = size;  
while (size > 0) {  
    len = s->buf_end - s->buf_ptr;  
    if (len > size)  
        len = size;  
    if (len == 0) {  
        if(size > s->buffer_size && !s->update_checksum){  
            if(s->read_packet)  
                //调用AVIOContext的成员  read_packet函数指针  
                len = s->read_packet(s->opaque, buf, size);  
            if (len <= 0) {  
                /* do not modify buffer if EOF reached so that a seek back can 
                be done without rereading data */  
                s->eof_reached = 1;  
                if(len<0)  
                    s->error= len;  
                break;  
            } else {  
                s->pos += len;  
                size -= len;  
                buf += len;  
                s->buf_ptr = s->buffer;  
                s->buf_end = s->buffer/* + len*/;  
            }  
        }else{  
            fill_buffer(s);  
            len = s->buf_end - s->buf_ptr;  
            if (len == 0)  
                break;  
        }  
    } else {  
        memcpy(buf, s->buf_ptr, len);  
        buf += len;  
        s->buf_ptr += len;  
        size -= len;  
    }  
}  
if (size1 == size) {  
    if (s->error)      return s->error;  
    if (url_feof(s))   return AVERROR_EOF;  
}  
return size1 - size;  

}

AVIOContext结构体需要由avformat_open_input来进行初始化。对于该函数打开媒体文件的分析，见收藏的一篇文章。目前根据需要要进行自定义的AVIOContext结构体变量的初始化。贴出ffmpeg初始化其的代码，参考进行自定义初始化。
[cpp] view plain copy
int ffio_fdopen(AVIOContext **s, URLContext *h)
{
uint8_t *buffer;
int buffer_size, max_packet_size;

max_packet_size = h->max_packet_size;  
if (max_packet_size) {  
    buffer_size = max_packet_size; /* no need to bufferize more than one packet */  
} else {  
    buffer_size = IO_BUFFER_SIZE;  
}  
buffer = av_malloc(buffer_size);  
if (!buffer)  
    return AVERROR(ENOMEM);  

*s = av_mallocz(sizeof(AVIOContext));  
if(!*s) {  
    av_free(buffer);  
    return AVERROR(ENOMEM);  
}  
//初始化AVIOContext  
if (ffio_init_context(*s, buffer, buffer_size,  
                  h->flags & AVIO_FLAG_WRITE, h,  
                  (void*)ffurl_read, (void*)ffurl_write, (void*)ffurl_seek) < 0) {  
    av_free(buffer);  
    av_freep(s);  
    return AVERROR(EIO);  
}  

if FF_API_OLD_AVIO

(*s)->is_streamed = h->is_streamed;  

endif

(*s)->seekable = h->is_streamed ? 0 : AVIO_SEEKABLE_NORMAL;  
(*s)->max_packet_size = max_packet_size;  
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;  
}  
return 0;  

}

int ffio_init_context(AVIOContext *s,
unsigned char *buffer,
int buffer_size,
int write_flag,
void *opaque,
int (*read_packet)(void *opaque, uint8_t *buf, int buf_size),
int (*write_packet)(void *opaque, uint8_t *buf, int buf_size),
int64_t (*seek)(void *opaque, int64_t offset, int whence))
{
s->buffer = buffer;
s->buffer_size = buffer_size;
s->buf_ptr = buffer;
s->opaque = opaque;
url_resetbuf(s, write_flag ? AVIO_FLAG_WRITE : AVIO_FLAG_READ);
s->write_packet = write_packet;
s->read_packet = read_packet;
s->seek = seek;
s->pos = 0;
s->must_flush = 0;
s->eof_reached = 0;
s->error = 0;

if FF_API_OLD_AVIO

s->is_streamed = 0;  

endif

s->seekable = AVIO_SEEKABLE_NORMAL;  
s->max_packet_size = 0;  
s->update_checksum= NULL;  
if(!read_packet && !write_flag){  
    s->pos = buffer_size;  
    s->buf_end = s->buffer + buffer_size;  
}  
s->read_pause = NULL;  
s->read_seek  = NULL;  
return 0;  

}
经过上述分析，需要根据项目需要自定义AVIOContext，设置数据源，设置各类回调函数。
网上找到一段探测网络流格式的方法，实现相似的功能。没有经过测试，先贴出来，后面进行测试。

[cpp] view plain copy

include “utils.h”

include

include

include

define BUF_SIZE 4096*500

int main(int argc, char** argv) {

init_queue(&recvqueue, 1024*500);

udpParam.argv = argv;
udpParam.queue = &recvqueue;
uint8_t *buf = av_mallocz(sizeof(uint8_t)*BUF_SIZE);

//UDP接收线程
pthread_t udp_recv_thread;
pthread_create(&udp_recv_thread, NULL, udp_ts_recv, &udpParam);
pthread_detach(udp_recv_thread);

av_register_all();

AVCodec *pVideoCodec, *pAudioCodec;
AVCodecContext *pVideoCodecCtx = NULL;
AVCodecContext *pAudioCodecCtx = NULL;
AVIOContext * pb = NULL;
AVInputFormat *piFmt = NULL;
AVFormatContext *pFmt = NULL;

//step1:申请一个AVIOContext
pb = avio_alloc_context(buf, BUF_SIZE, 0, NULL, read_data, NULL, NULL);
if (!pb) {
fprintf(stderr, “avio alloc failed!\n”);
return -1;
}
//step2:探测流格式
if (av_probe_input_buffer(pb, &piFmt, “”, NULL, 0, 0) < 0) {
fprintf(stderr, “probe failed!\n”);
return -1;
} else {
fprintf(stdout, “probe success!\n”);
fprintf(stdout, “format: %s[%s]\n”, piFmt->name, piFmt->long_name);
}

pFmt = avformat_alloc_context();
pFmt->pb = pb; //step3:这一步很关键
//step4:打开流
if (avformat_open_input(&pFmt, “”, piFmt, NULL) < 0) {
fprintf(stderr, “avformat open failed.\n”);
return -1;
} else {
fprintf(stdout, “open stream success!\n”);
}
//以下就和文件处理一致了
if (av_find_stream_info(pFmt) < 0) {
fprintf(stderr, “could not fine stream.\n”);
return -1;
}

av_dump_format(pFmt, 0, “”, 0);

int videoindex = -1;
int audioindex = -1;
for (int i = 0; i < pFmt->nb_streams; i++) {
if ( (pFmt->streams[i]->codec->codec_type == AVMEDIA_TYPE_VIDEO) &&
(videoindex < 0) ) {
videoindex = i;
}
if ( (pFmt->streams[i]->codec->codec_type == AVMEDIA_TYPE_AUDIO) &&
(audioindex < 0) ) {
audioindex = i;
}
}

if (videoindex < 0 || audioindex < 0) {
fprintf(stderr, “videoindex=%d, audioindex=%d\n”, videoindex, audioindex);
return -1;
}

AVStream *pVst,*pAst;
pVst = pFmt->streams[videoindex];
pAst = pFmt->streams[audioindex];

pVideoCodecCtx = pVst->codec;
pAudioCodecCtx = pAst->codec;

pVideoCodec = avcodec_find_decoder(pVideoCodecCtx->codec_id);
if (!pVideoCodec) {
fprintf(stderr, “could not find video decoder!\n”);
return -1;
}
if (avcodec_open(pVideoCodecCtx, pVideoCodec) < 0) {
fprintf(stderr, “could not open video codec!\n”);
return -1;
}

pAudioCodec = avcodec_find_decoder(pAudioCodecCtx->codec_id);
if (!pAudioCodec) {
fprintf(stderr, “could not find audio decoder!\n”);
return -1;
}
if (avcodec_open(pAudioCodecCtx, pAudioCodec) < 0) {
fprintf(stderr, “could not open audio codec!\n”);
return -1;
}

int got_picture;
uint8_t samples[AVCODEC_MAX_AUDIO_FRAME_SIZE*3/2];
AVFrame *pframe = avcodec_alloc_frame();
AVPacket pkt;
av_init_packet(&pkt);

while(1) {
if (av_read_frame(pFmt, &pkt) >= 0) {

if (pkt.stream_index == videoindex) {
fprintf(stdout, “pkt.size=%d,pkt.pts=%lld, pkt.data=0x%x.”, pkt.size, pkt.pts,(unsigned int)pkt.data);
avcodec_decode_video2(pVideoCodecCtx, pframe, &got_picture, &pkt);
if (got_picture) {
fprintf(stdout, “decode one video frame!\n”);
}
}else if (pkt.stream_index == audioindex) {
int frame_size = AVCODEC_MAX_AUDIO_FRAME_SIZE*3/2;
if (avcodec_decode_audio3(pAudioCodecCtx, (int16_t *)samples, &frame_size, &pkt) >= 0) {
fprintf(stdout, “decode one audio frame!\n”);
}
}
av_free_packet(&pkt);
}
}

av_free(buf);
av_free(pframe);
free_queue(&recvqueue);
return 0;
}
这段代码作者为windragon0419，在此表示感谢。
后面经过测试以后，记录下解决过程。