utils.c

ffmpeg的完整源代码和作者自己写的文档。不但有在Linux的工程哦

/** Size of probe buffer, for guessing file type from file contents. */
#define PROBE_BUF_MIN 2048
#define PROBE_BUF_MAX (1<<20)

int av_open_input_file(AVFormatContext **ic_ptr, const char *filename,
                       AVInputFormat *fmt,
                       int buf_size,
                       AVFormatParameters *ap)
{
    int err, must_open_file, file_opened, probe_size;
    AVProbeData probe_data, *pd = &probe_data;
    ByteIOContext pb1, *pb = &pb1;

    file_opened = 0;
    pd->filename = "";
    if (filename)
        pd->filename = filename;
    pd->buf = NULL;
    pd->buf_size = 0;

    if (!fmt) {
        /* guess format if no file can be opened  */
        fmt = av_probe_input_format(pd, 0);
    }

    /* do not open file if the format does not need it. XXX: specific
       hack needed to handle RTSP/TCP */
    must_open_file = 1;
    if (fmt && (fmt->flags & AVFMT_NOFILE)) {
        must_open_file = 0;
        pb= NULL; //FIXME this or memset(pb, 0, sizeof(ByteIOContext)); otherwise it is uninitialized
    }

    if (!fmt || must_open_file) {
        /* if no file needed do not try to open one */
        if ((err=url_fopen(pb, filename, URL_RDONLY)) < 0) {
            goto fail;
        }
        file_opened = 1;
        if (buf_size > 0) {
            url_setbufsize(pb, buf_size);
        }

        for(probe_size= PROBE_BUF_MIN; probe_size<=PROBE_BUF_MAX && !fmt; probe_size<<=1){
            int score= probe_size < PROBE_BUF_MAX ? AVPROBE_SCORE_MAX/4 : 0;
            /* read probe data */
            pd->buf= av_realloc(pd->buf, probe_size + AVPROBE_PADDING_SIZE);
            pd->buf_size = get_buffer(pb, pd->buf, probe_size);
            memset(pd->buf+pd->buf_size, 0, AVPROBE_PADDING_SIZE);
            if (url_fseek(pb, 0, SEEK_SET) < 0) {
                url_fclose(pb);
                if (url_fopen(pb, filename, URL_RDONLY) < 0) {
                    file_opened = 0;
                    err = AVERROR(EIO);
                    goto fail;
                }
            }
            /* guess file format */
            fmt = av_probe_input_format2(pd, 1, &score);
        }
        av_freep(&pd->buf);
    }

    /* if still no format found, error */
    if (!fmt) {
        err = AVERROR_NOFMT;
        goto fail;
    }

    /* XXX: suppress this hack for redirectors */
#ifdef CONFIG_REDIR_DEMUXER
    if (!strcmp(fmt->name, "redir")) {
        int redir_open(AVFormatContext **ic_ptr, ByteIOContext *f);
        err = redir_open(ic_ptr, pb);
        url_fclose(pb);
        return err;
    }
#endif

    /* check filename in case of an image number is expected */
    if (fmt->flags & AVFMT_NEEDNUMBER) {
        if (!av_filename_number_test(filename)) {
            err = AVERROR_NUMEXPECTED;
            goto fail;
        }
    }
    err = av_open_input_stream(ic_ptr, pb, filename, fmt, ap);
    if (err)
        goto fail;
    return 0;
 fail:
    av_freep(&pd->buf);
    if (file_opened)
        url_fclose(pb);
    *ic_ptr = NULL;
    return err;

}

/*******************************************************/

int av_read_packet(AVFormatContext *s, AVPacket *pkt)
{
    av_init_packet(pkt);
    return s->iformat->read_packet(s, pkt);
}

/**********************************************************/

/**
 * Get the number of samples of an audio frame. Return (-1) if error.
 */
static int get_audio_frame_size(AVCodecContext *enc, int size)
{
    int frame_size;

    if (enc->frame_size <= 1) {
        int bits_per_sample = av_get_bits_per_sample(enc->codec_id);

        if (bits_per_sample) {
            if (enc->channels == 0)
                return -1;
            frame_size = (size << 3) / (bits_per_sample * enc->channels);
        } else {
            /* used for example by ADPCM codecs */
            if (enc->bit_rate == 0)
                return -1;
            frame_size = (size * 8 * enc->sample_rate) / enc->bit_rate;
        }
    } else {
        frame_size = enc->frame_size;
    }
    return frame_size;
}


/**
 * Return the frame duration in seconds, return 0 if not available.
 */
static void compute_frame_duration(int *pnum, int *pden, AVStream *st,
                                   AVCodecParserContext *pc, AVPacket *pkt)
{
    int frame_size;

    *pnum = 0;
    *pden = 0;
    switch(st->codec->codec_type) {
    case CODEC_TYPE_VIDEO:
        if(st->time_base.num*1000LL > st->time_base.den){
            *pnum = st->time_base.num;
            *pden = st->time_base.den;
        }else if(st->codec->time_base.num*1000LL > st->codec->time_base.den){
            *pnum = st->codec->time_base.num;
            *pden = st->codec->time_base.den;
            if (pc && pc->repeat_pict) {
                *pden *= 2;
                *pnum = (*pnum) * (2 + pc->repeat_pict);
            }
        }
        break;
    case CODEC_TYPE_AUDIO:
        frame_size = get_audio_frame_size(st->codec, pkt->size);
        if (frame_size < 0)
            break;
        *pnum = frame_size;
        *pden = st->codec->sample_rate;
        break;
    default:
        break;
    }
}

static int is_intra_only(AVCodecContext *enc){
    if(enc->codec_type == CODEC_TYPE_AUDIO){
        return 1;
    }else if(enc->codec_type == CODEC_TYPE_VIDEO){
        switch(enc->codec_id){
        case CODEC_ID_MJPEG:
        case CODEC_ID_MJPEGB:
        case CODEC_ID_LJPEG:
        case CODEC_ID_RAWVIDEO:
        case CODEC_ID_DVVIDEO:
        case CODEC_ID_HUFFYUV:
        case CODEC_ID_FFVHUFF:
        case CODEC_ID_ASV1:
        case CODEC_ID_ASV2:
        case CODEC_ID_VCR1:
            return 1;
        default: break;
        }
    }
    return 0;
}

static void update_initial_timestamps(AVFormatContext *s, int stream_index,
                                      int64_t dts, int64_t pts)
{
    AVStream *st= s->streams[stream_index];
    AVPacketList *pktl= s->packet_buffer;

    if(st->first_dts != AV_NOPTS_VALUE || dts == AV_NOPTS_VALUE)
        return;

    st->first_dts= dts - st->cur_dts;
    st->cur_dts= dts;

    for(; pktl; pktl= pktl->next){
        if(pktl->pkt.stream_index != stream_index)
            continue;
        //FIXME think more about this check
        if(pktl->pkt.pts != AV_NOPTS_VALUE && pktl->pkt.pts == pktl->pkt.dts)
            pktl->pkt.pts += st->first_dts;

        if(pktl->pkt.dts != AV_NOPTS_VALUE)
            pktl->pkt.dts += st->first_dts;

        if(st->start_time == AV_NOPTS_VALUE && pktl->pkt.pts != AV_NOPTS_VALUE)
            st->start_time= pktl->pkt.pts;
    }
    if (st->start_time == AV_NOPTS_VALUE)
        st->start_time = pts;
}

static void compute_pkt_fields(AVFormatContext *s, AVStream *st,
                               AVCodecParserContext *pc, AVPacket *pkt)
{
    int num, den, presentation_delayed, delay, i;
    int64_t offset;

    if(pkt->pts != AV_NOPTS_VALUE && pkt->dts != AV_NOPTS_VALUE && pkt->dts > pkt->pts && st->pts_wrap_bits<63
       /*&& pkt->dts-(1LL<<st->pts_wrap_bits) < pkt->pts*/){
        pkt->dts -= 1LL<<st->pts_wrap_bits;
    }

    if (pkt->duration == 0) {
        compute_frame_duration(&num, &den, st, pc, pkt);
        if (den && num) {
            pkt->duration = av_rescale(1, num * (int64_t)st->time_base.den, den * (int64_t)st->time_base.num);
        }
    }

    /* correct timestamps with byte offset if demuxers only have timestamps on packet boundaries */
    if(pc && st->need_parsing == AVSTREAM_PARSE_TIMESTAMPS && pkt->size){
        /* this will estimate bitrate based on this frame's duration and size */
        offset = av_rescale(pc->offset, pkt->duration, pkt->size);
        if(pkt->pts != AV_NOPTS_VALUE)
            pkt->pts += offset;
        if(pkt->dts != AV_NOPTS_VALUE)
            pkt->dts += offset;
    }

    if(is_intra_only(st->codec))
        pkt->flags |= PKT_FLAG_KEY;

    /* do we have a video B frame ? */
    delay= st->codec->has_b_frames;
    presentation_delayed = 0;
    /* XXX: need has_b_frame, but cannot get it if the codec is
        not initialized */
    if (delay &&
        pc && pc->pict_type != FF_B_TYPE)
        presentation_delayed = 1;
    /* This may be redundant, but it should not hurt. */
    if(pkt->dts != AV_NOPTS_VALUE && pkt->pts != AV_NOPTS_VALUE && pkt->pts > pkt->dts)
        presentation_delayed = 1;

    if(st->cur_dts == AV_NOPTS_VALUE){
        st->cur_dts = 0; //FIXME maybe set it to 0 during init
    }

//    av_log(NULL, AV_LOG_DEBUG, "IN delayed:%d pts:%"PRId64", dts:%"PRId64" cur_dts:%"PRId64" st:%d pc:%p\n", presentation_delayed, pkt->pts, pkt->dts, st->cur_dts, pkt->stream_index, pc);
    /* interpolate PTS and DTS if they are not present */
    if(delay <=1){
        if (presentation_delayed) {
            /* DTS = decompression time stamp */
            /* PTS = presentation time stamp */
            if (pkt->dts == AV_NOPTS_VALUE)
                pkt->dts = st->last_IP_pts;
            update_initial_timestamps(s, pkt->stream_index, pkt->dts, pkt->pts);
            if (pkt->dts == AV_NOPTS_VALUE)
                pkt->dts = st->cur_dts;

            /* this is tricky: the dts must be incremented by the duration
            of the frame we are displaying, i.e. the last I or P frame */
            if (st->last_IP_duration == 0)
                st->last_IP_duration = pkt->duration;
            st->cur_dts = pkt->dts + st->last_IP_duration;
            st->last_IP_duration  = pkt->duration;
            st->last_IP_pts= pkt->pts;
            /* cannot compute PTS if not present (we can compute it only
            by knowing the futur */
        } else if(pkt->pts != AV_NOPTS_VALUE || pkt->dts != AV_NOPTS_VALUE || pkt->duration){
            if(pkt->pts != AV_NOPTS_VALUE && pkt->duration){
                int64_t old_diff= FFABS(st->cur_dts - pkt->duration - pkt->pts);
                int64_t new_diff= FFABS(st->cur_dts - pkt->pts);
                if(old_diff < new_diff && old_diff < (pkt->duration>>3)){
                    pkt->pts += pkt->duration;
    //                av_log(NULL, AV_LOG_DEBUG, "id:%d old:%"PRId64" new:%"PRId64" dur:%d cur:%"PRId64" size:%d\n", pkt->stream_index, old_diff, new_diff, pkt->duration, st->cur_dts, pkt->size);
                }
            }

            /* presentation is not delayed : PTS and DTS are the same */
            if(pkt->pts == AV_NOPTS_VALUE)
                pkt->pts = pkt->dts;
            update_initial_timestamps(s, pkt->stream_index, pkt->pts, pkt->pts);
            if(pkt->pts == AV_NOPTS_VALUE)
                pkt->pts = st->cur_dts;
            pkt->dts = pkt->pts;
            st->cur_dts = pkt->pts + pkt->duration;
        }
    }

    if(pkt->pts != AV_NOPTS_VALUE){
        st->pts_buffer[0]= pkt->pts;
        for(i=1; i<delay+1 && st->pts_buffer[i] == AV_NOPTS_VALUE; i++)
            st->pts_buffer[i]= (i-delay-1) * pkt->duration;
        for(i=0; i<delay && st->pts_buffer[i] > st->pts_buffer[i+1]; i++)
            FFSWAP(int64_t, st->pts_buffer[i], st->pts_buffer[i+1]);
        if(pkt->dts == AV_NOPTS_VALUE)
            pkt->dts= st->pts_buffer[0];
        if(delay>1){
            update_initial_timestamps(s, pkt->stream_index, pkt->dts, pkt->pts); // this should happen on the first packet
        }
        if(pkt->dts > st->cur_dts)
            st->cur_dts = pkt->dts;
    }

//    av_log(NULL, AV_LOG_ERROR, "OUTdelayed:%d/%d pts:%"PRId64", dts:%"PRId64" cur_dts:%"PRId64"\n", presentation_delayed, delay, pkt->pts, pkt->dts, st->cur_dts);

    /* update flags */
    if (pc) {
        pkt->flags = 0;
        /* key frame computation */
            if (pc->pict_type == FF_I_TYPE)
                pkt->flags |= PKT_FLAG_KEY;
    }
}

void av_destruct_packet_nofree(AVPacket *pkt)
{
    pkt->data = NULL; pkt->size = 0;
}

static int av_read_frame_internal(AVFormatContext *s, AVPacket *pkt)
{
    AVStream *st;
    int len, ret, i;

    av_init_packet(pkt);

    for(;;) {
        /* select current input stream component */
        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 = s->cur_pkt;
                compute_pkt_fields(s, st, NULL, pkt);
                s->cur_st = NULL;
                break;
            } else if (s->cur_len > 0 && st->discard < AVDISCARD_ALL) {
                len = av_parser_parse(st->parser, st->codec, &pkt->data, &pkt->size,
                                      s->cur_ptr, s->cur_len,
                                      s->cur_pkt.pts, s->cur_pkt.dts);
                s->cur_pkt.pts = AV_NOPTS_VALUE;
                s->cur_pkt.dts = AV_NOPTS_VALUE;
                /* increment read pointer */
                s->cur_ptr += len;
                s->cur_len -= len;

                /* return packet if any */
                if (pkt->size) {
                got_packet:
                    pkt->pos = s->cur_pkt.pos;              // Isn't quite accurate but close.
                    pkt->duration = 0;
                    pkt->stream_index = st->index;
                    pkt->pts = st->parser->pts;
                    pkt->dts = st->parser->dts;
                    pkt->destruct = av_destruct_packet_nofree;
                    compute_pkt_fields(s, st, st->parser, pkt);

                    if((s->iformat->flags & AVFMT_GENERIC_INDEX) && pkt->flags & PKT_FLAG_KEY){
                        av_add_index_entry(st, st->parser->frame_offset, pkt->dts,
                                           0, 0, AVINDEX_KEYFRAME);
                    }

                    break;
                }
            } else {
                /* free packet */
                av_free_packet(&s->cur_pkt);
                s->cur_st = NULL;
            }
        } else {
            /* read next packet */
            ret = av_read_packet(s, &s->cur_pkt);
            if (ret < 0) {