utils.c

ffmpeg源码分析

            break;
        }
    }
}

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;

    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;
                return 0;
            } 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->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);
                    return 0;
                }
            } 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) {
                if (ret == -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_parse(st->parser, st->codec,
                                        &pkt->data, &pkt->size,
                                        NULL, 0,
                                        AV_NOPTS_VALUE, AV_NOPTS_VALUE);
                        if (pkt->size)
                            goto got_packet;
                    }
                }
                /* no more packets: really terminates parsing */
                return ret;
            }

            st = s->streams[s->cur_pkt.stream_index];

            s->cur_st = st;
            s->cur_ptr = s->cur_pkt.data;
            s->cur_len = s->cur_pkt.size;
            if (st->need_parsing && !st->parser) {
                st->parser = av_parser_init(st->codec->codec_id);
                if (!st->parser) {
                    /* no parser available : just output the raw packets */
                    st->need_parsing = 0;
                }else if(st->need_parsing == 2){
                    st->parser->flags |= PARSER_FLAG_COMPLETE_FRAMES;
                }
            }
        }
    }
}

/**
 * Return the next frame of a stream.
 *
 * The returned packet is valid
 * until the next av_read_frame() or until av_close_input_file() and
 * must be freed with av_free_packet. For video, the packet contains
 * exactly one frame. For audio, it contains an integer number of
 * frames if each frame has a known fixed size (e.g. PCM or ADPCM
 * data). If the audio frames have a variable size (e.g. MPEG audio),
 * then it contains one frame.
 *
 * pkt->pts, pkt->dts and pkt->duration are always set to correct
 * values in AV_TIME_BASE unit (and guessed if the format cannot
 * provided them). pkt->pts can be AV_NOPTS_VALUE if the video format
 * has B frames, so it is better to rely on pkt->dts if you do not
 * decompress the payload.
 *
 * @return 0 if OK, < 0 if error or end of file.
 */
int av_read_frame(AVFormatContext *s, AVPacket *pkt)
{
    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){
                while(pktl && next_pkt->pts == AV_NOPTS_VALUE){
                    if(   pktl->pkt.stream_index == next_pkt->stream_index
                       && next_pkt->dts < pktl->pkt.dts
                       && pktl->pkt.pts != pktl->pkt.dts //not b frame
                       /*&& pktl->pkt.dts != AV_NOPTS_VALUE*/){
                        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){
            AVPacketList **plast_pktl= &s->packet_buffer;
            int ret= av_read_frame_internal(s, pkt);
            if(ret<0){
                if(pktl && ret != -EAGAIN){
                    eof=1;
                    continue;
                }else
                    return ret;
            }

            /* duplicate the packet */
            if (av_dup_packet(pkt) < 0)
                return AVERROR_NOMEM;

            while(*plast_pktl) plast_pktl= &(*plast_pktl)->next; //FIXME maybe maintain pointer to the last?

            pktl = av_mallocz(sizeof(AVPacketList));
            if (!pktl)
                return AVERROR_NOMEM;

            /* add the packet in the buffered packet list */
            *plast_pktl = pktl;
            pktl->pkt= *pkt;
        }else{
            assert(!s->packet_buffer);
            return av_read_frame_internal(s, pkt);
        }
    }
}

/* XXX: suppress the packet queue */
static void flush_packet_queue(AVFormatContext *s)
{
    AVPacketList *pktl;

    for(;;) {
        pktl = s->packet_buffer;
        if (!pktl)
            break;
        s->packet_buffer = pktl->next;
        av_free_packet(&pktl->pkt);
        av_free(pktl);
    }
}

/*******************************************************/
/* seek support */

int av_find_default_stream_index(AVFormatContext *s)
{
    int i;
    AVStream *st;

    if (s->nb_streams <= 0)
        return -1;
    for(i = 0; i < s->nb_streams; i++) {
        st = s->streams[i];
        if (st->codec->codec_type == CODEC_TYPE_VIDEO) {
            return i;
        }
    }
    return 0;
}

/**
 * Flush the frame reader.
 */
static void av_read_frame_flush(AVFormatContext *s)
{
    AVStream *st;
    int i;

    flush_packet_queue(s);

    /* free previous packet */
    if (s->cur_st) {
        if (s->cur_st->parser)
            av_free_packet(&s->cur_pkt);
        s->cur_st = NULL;
    }
    /* fail safe */
    s->cur_ptr = NULL;
    s->cur_len = 0;

    /* for each stream, reset read state */
    for(i = 0; i < s->nb_streams; i++) {
        st = s->streams[i];

        if (st->parser) {
            av_parser_close(st->parser);
            st->parser = NULL;
        }
        st->last_IP_pts = AV_NOPTS_VALUE;
        st->cur_dts = 0; /* we set the current DTS to an unspecified origin */
    }
}

/**
 * Updates cur_dts of all streams based on given timestamp and AVStream.
 *
 * Stream ref_st unchanged, others set cur_dts in their native timebase
 * only needed for timestamp wrapping or if (dts not set and pts!=dts)
 * @param timestamp new dts expressed in time_base of param ref_st
 * @param ref_st reference stream giving time_base of param timestamp
 */
static void av_update_cur_dts(AVFormatContext *s, AVStream *ref_st, int64_t timestamp){
    int i;

    for(i = 0; i < s->nb_streams; i++) {
        AVStream *st = s->streams[i];

        st->cur_dts = av_rescale(timestamp,
                                 st->time_base.den * (int64_t)ref_st->time_base.num,
                                 st->time_base.num * (int64_t)ref_st->time_base.den);
    }
}

/**
 * Add a index entry into a sorted list updateing if it is already there.
 *
 * @param timestamp timestamp in the timebase of the given stream
 */
int av_add_index_entry(AVStream *st,
                            int64_t pos, int64_t timestamp, int size, int distance, int flags)
{
    AVIndexEntry *entries, *ie;
    int index;

    if((unsigned)st->nb_index_entries + 1 >= UINT_MAX / sizeof(AVIndexEntry))
        return -1;

    entries = av_fast_realloc(st->index_entries,
                              &st->index_entries_allocated_size,
                              (st->nb_index_entries + 1) *
                              sizeof(AVIndexEntry));
    if(!entries)
        return -1;

    st->index_entries= entries;

    index= av_index_search_timestamp(st, timestamp, AVSEEK_FLAG_ANY);

    if(index<0){
        index= st->nb_index_entries++;
        ie= &entries[index];
        assert(index==0 || ie[-1].timestamp < timestamp);
    }else{
        ie= &entries[index];
        if(ie->timestamp != timestamp){
            if(ie->timestamp <= timestamp)
                return -1;
            memmove(entries + index + 1, entries + index, sizeof(AVIndexEntry)*(st->nb_index_entries - index));
            st->nb_index_entries++;
        }else if(ie->pos == pos && distance < ie->min_distance) //dont reduce the distance
            distance= ie->min_distance;
    }

    ie->pos = pos;
    ie->timestamp = timestamp;
    ie->min_distance= distance;
    ie->size= size;
    ie->flags = flags;

    return index;
}

/**
 * build an index for raw streams using a parser.
 */
static void av_build_index_raw(AVFormatContext *s)
{
    AVPacket pkt1, *pkt = &pkt1;
    int ret;
    AVStream *st;

    st = s->streams[0];
    av_read_frame_flush(s);
    url_fseek(&s->pb, s->data_offset, SEEK_SET);

    for(;;) {
        ret = av_read_frame(s, pkt);
        if (ret < 0)
            break;
        if (pkt->stream_index == 0 && st->parser &&
            (pkt->flags & PKT_FLAG_KEY)) {
            av_add_index_entry(st, st->parser->frame_offset, pkt->dts,
                            0, 0, AVINDEX_KEYFRAME);
        }
        av_free_packet(pkt);
    }
}

/**
 * Returns TRUE if we deal with a raw stream.
 *
 * Raw codec data and parsing needed.
 */
static int is_raw_stream(AVFormatContext *s)
{
    AVStream *st;

    if (s->nb_streams != 1)
        return 0;
    st = s->streams[0];
    if (!st->need_parsing)
        return 0;
    return 1;
}

/**
 * Gets the index for a specific timestamp.
 * @param flags if AVSEEK_FLAG_BACKWARD then the returned index will correspond to
 *                 the timestamp which is <= the requested one, if backward is 0
 *                 then it will be >=
 *              if AVSEEK_FLAG_ANY seek to any frame, only keyframes otherwise
 * @return < 0 if no such timestamp could be found
 */
int av_index_search_timestamp(AVStream *st, int64_t wanted_timestamp,
                              int flags)
{
    AVIndexEntry *entries= st->index_entries;
    int nb_entries= st->nb_index_entries;
    int a, b, m;
    int64_t timestamp;

    a = - 1;
    b = nb_entries;

    while (b - a > 1) {
        m = (a + b) >> 1;
        timestamp = entries[m].timestamp;
        if(timestamp >= wanted_timestamp)
            b = m;
        if(timestamp <= wanted_timestamp)
            a = m;
    }
    m= (flags & AVSEEK_FLAG_BACKWARD) ? a : b;

    if(!(flags & AVSEEK_FLAG_ANY)){
        while(m>=0 && m<nb_entries && !(entries[m].flags & AVINDEX_KEYFRAME)){
            m += (flags & AVSEEK_FLAG_BACKWARD) ? -1 : 1;
        }
    }

    if(m == nb_entries)
        return -1;
    return  m;
}

#define DEBUG_SEEK

/**
 * Does a binary search using av_index_search_timestamp() and AVCodec.read_timestamp().
 * this isnt supposed to be called directly by a user application, but by demuxers
 * @param target_ts target timestamp in the time base of the given stream
 * @param stream_index stream number
 */
int av_seek_frame_binary(AVFormatContext *s, int stream_index, int64_t target_ts, int flags){
    AVInputFormat *avif= s->iformat;
    int64_t pos_min, pos_max, pos, pos_limit;
    int64_t ts_min, ts_max, ts;
    int64_t start_pos, filesize;
    int index, no_change;
    AVStream *st;

    if (stream_index < 0)
        return -1;

#ifdef DEBUG_SEEK
    av_log(s, AV_LOG_DEBUG, "read_seek: %d %"PRId64"\n", stream_index, target_ts);
#endif

    ts_max=
    ts_min= AV_NOPTS_VALUE;
    pos_limit= -1; //gcc falsely says it may be uninitalized

    st= s->streams[stream_index];
    if(st->index_entries){
        AVIndexEntry *e;

        index= av_index_search_timestamp(st, target_ts, flags | AVSEEK_FLAG_BACKWARD); //FIXME whole func must be checked for non keyframe entries in index case, especially read_timestamp()
        index= FFMAX(index, 0);
        e= &st->index_entries[index];

        if(e->timestamp <= target_ts || e->pos == e->min_distance){
            pos_min= e->pos;
            ts_min= e->timestamp;
#ifdef DEBUG_SEEK
        av_log(s, AV_LOG_DEBUG, "using cached pos_min=0x%"PRIx64" dts_min=%"PRId64"\n",