utils.c

/*
 * Various utilities for ffmpeg system
 * Copyright (c) 2000, 2001, 2002 Fabrice Bellard
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 */
#include "avformat.h"

#undef NDEBUG
#include <assert.h>

AVInputFormat *first_iformat = NULL;
AVOutputFormat *first_oformat = NULL;
AVImageFormat *first_image_format = NULL;

void av_register_input_format(AVInputFormat *format)
{
    AVInputFormat **p;
    p = &first_iformat;
    while (*p != NULL) p = &(*p)->next;
    *p = format;
    format->next = NULL;
}

void av_register_output_format(AVOutputFormat *format)
{
    AVOutputFormat **p;
    p = &first_oformat;
    while (*p != NULL) p = &(*p)->next;
    *p = format;
    format->next = NULL;
}

int match_ext(const char *filename, const char *extensions)
{
    const char *ext, *p;
    char ext1[32], *q;

    if(!filename)
        return 0;
    
    ext = strrchr(filename, '.');
    if (ext) {
        ext++;
        p = extensions;
        for(;;) {
            q = ext1;
            while (*p != '\0' && *p != ',') 
                *q++ = *p++;
            *q = '\0';
            if (!strcasecmp(ext1, ext)) 
                return 1;
            if (*p == '\0') 
                break;
            p++;
        }
    }
    return 0;
}

AVOutputFormat *guess_format(const char *short_name, const char *filename, 
                             const char *mime_type)
{
    AVOutputFormat *fmt, *fmt_found;
    int score_max, score;

    /* specific test for image sequences */
    if (!short_name && filename && 
        filename_number_test(filename) >= 0 &&
        av_guess_image2_codec(filename) != CODEC_ID_NONE) {
        return guess_format("image2", NULL, NULL);
    }
    if (!short_name && filename && 
        filename_number_test(filename) >= 0 &&
        guess_image_format(filename)) {
        return guess_format("image", NULL, NULL);
    }

    /* find the proper file type */
    fmt_found = NULL;
    score_max = 0;
    fmt = first_oformat;
    while (fmt != NULL) {
        score = 0;
        if (fmt->name && short_name && !strcmp(fmt->name, short_name))
            score += 100;
        if (fmt->mime_type && mime_type && !strcmp(fmt->mime_type, mime_type))
            score += 10;
        if (filename && fmt->extensions && 
            match_ext(filename, fmt->extensions)) {
            score += 5;
        }
        if (score > score_max) {
            score_max = score;
            fmt_found = fmt;
        }
        fmt = fmt->next;
    }
    return fmt_found;
}   

AVOutputFormat *guess_stream_format(const char *short_name, const char *filename, 
                             const char *mime_type)
{
    AVOutputFormat *fmt = guess_format(short_name, filename, mime_type);

    if (fmt) {
        AVOutputFormat *stream_fmt;
        char stream_format_name[64];

        snprintf(stream_format_name, sizeof(stream_format_name), "%s_stream", fmt->name);
        stream_fmt = guess_format(stream_format_name, NULL, NULL);

        if (stream_fmt)
            fmt = stream_fmt;
    }

    return fmt;
}

/**
 * guesses the codec id based upon muxer and filename.
 */
enum CodecID av_guess_codec(AVOutputFormat *fmt, const char *short_name, 
                            const char *filename, const char *mime_type, enum CodecType type){
    if(type == CODEC_TYPE_VIDEO){
        enum CodecID codec_id= CODEC_ID_NONE;

        if(!strcmp(fmt->name, "image2") || !strcmp(fmt->name, "image2pipe")){
            codec_id= av_guess_image2_codec(filename);
        }
        if(codec_id == CODEC_ID_NONE)
            codec_id= fmt->video_codec;
        return codec_id;
    }else if(type == CODEC_TYPE_AUDIO)
        return fmt->audio_codec;
    else
        return CODEC_ID_NONE;
}

AVInputFormat *av_find_input_format(const char *short_name)
{
    AVInputFormat *fmt;
    for(fmt = first_iformat; fmt != NULL; fmt = fmt->next) {
        if (!strcmp(fmt->name, short_name))
            return fmt;
    }
    return NULL;
}

/* memory handling */

/**
 * Default packet destructor 
 */
static void av_destruct_packet(AVPacket *pkt)
{
    av_free(pkt->data);
    pkt->data = NULL; pkt->size = 0;
}

/**
 * Allocate the payload of a packet and intialized its fields to default values.
 *
 * @param pkt packet
 * @param size wanted payload size
 * @return 0 if OK. AVERROR_xxx otherwise.
 */
int av_new_packet(AVPacket *pkt, int size)
{
    void *data = av_malloc(size + FF_INPUT_BUFFER_PADDING_SIZE);
    if (!data)
        return AVERROR_NOMEM;
    memset(data + size, 0, FF_INPUT_BUFFER_PADDING_SIZE);

    av_init_packet(pkt);
    pkt->data = data; 
    pkt->size = size;
    pkt->destruct = av_destruct_packet;
    return 0;
}

/* This is a hack - the packet memory allocation stuff is broken. The
   packet is allocated if it was not really allocated */
int av_dup_packet(AVPacket *pkt)
{
    if (pkt->destruct != av_destruct_packet) {
        uint8_t *data;
        /* we duplicate the packet and don't forget to put the padding
           again */
        data = av_malloc(pkt->size + FF_INPUT_BUFFER_PADDING_SIZE);
        if (!data) {
            return AVERROR_NOMEM;
        }
        memcpy(data, pkt->data, pkt->size);
        memset(data + pkt->size, 0, FF_INPUT_BUFFER_PADDING_SIZE);
        pkt->data = data;
        pkt->destruct = av_destruct_packet;
    }
    return 0;
}

/* fifo handling */

int fifo_init(FifoBuffer *f, int size)
{
    f->buffer = av_malloc(size);
    if (!f->buffer)
        return -1;
    f->end = f->buffer + size;
    f->wptr = f->rptr = f->buffer;
    return 0;
}

void fifo_free(FifoBuffer *f)
{
    av_free(f->buffer);
}

int fifo_size(FifoBuffer *f, uint8_t *rptr)
{
    int size;
    
    if(!rptr)
        rptr= f->rptr;

    if (f->wptr >= rptr) {
        size = f->wptr - rptr;
    } else {
        size = (f->end - rptr) + (f->wptr - f->buffer);
    }
    return size;
}

/* get data from the fifo (return -1 if not enough data) */
int fifo_read(FifoBuffer *f, uint8_t *buf, int buf_size, uint8_t **rptr_ptr)
{
    uint8_t *rptr;
    int size, len;

    if(!rptr_ptr)
        rptr_ptr= &f->rptr;
    rptr = *rptr_ptr;

    if (f->wptr >= rptr) {
        size = f->wptr - rptr;
    } else {
        size = (f->end - rptr) + (f->wptr - f->buffer);
    }
    
    if (size < buf_size)
        return -1;
    while (buf_size > 0) {
        len = f->end - rptr;
        if (len > buf_size)
            len = buf_size;
        memcpy(buf, rptr, len);
        buf += len;
        rptr += len;
        if (rptr >= f->end)
            rptr = f->buffer;
        buf_size -= len;
    }
    *rptr_ptr = rptr;
    return 0;
}

void fifo_realloc(FifoBuffer *f, int new_size){
    int old_size= f->end - f->buffer;
    
    if(old_size < new_size){
        uint8_t *old= f->buffer;

        f->buffer= av_realloc(f->buffer, new_size);

        f->rptr += f->buffer - old;
        f->wptr += f->buffer - old;

        if(f->wptr < f->rptr){
            memmove(f->rptr + new_size - old_size, f->rptr, f->buffer + old_size - f->rptr);
            f->rptr += new_size - old_size;
        }
        f->end= f->buffer + new_size;
    }
}

void fifo_write(FifoBuffer *f, uint8_t *buf, int size, uint8_t **wptr_ptr)
{
    int len;
    uint8_t *wptr;

    if(!wptr_ptr)
        wptr_ptr= &f->wptr;
    wptr = *wptr_ptr;

    while (size > 0) {
        len = f->end - wptr;
        if (len > size)
            len = size;
        memcpy(wptr, buf, len);
        wptr += len;
        if (wptr >= f->end)
            wptr = f->buffer;
        buf += len;
        size -= len;
    }
    *wptr_ptr = wptr;
}

/* get data from the fifo (return -1 if not enough data) */
int put_fifo(ByteIOContext *pb, FifoBuffer *f, int buf_size, uint8_t **rptr_ptr)
{
    uint8_t *rptr = *rptr_ptr;
    int size, len;

    if (f->wptr >= rptr) {
        size = f->wptr - rptr;
    } else {
        size = (f->end - rptr) + (f->wptr - f->buffer);
    }
    
    if (size < buf_size)
        return -1;
    while (buf_size > 0) {
        len = f->end - rptr;
        if (len > buf_size)
            len = buf_size;
        put_buffer(pb, rptr, len);
        rptr += len;
        if (rptr >= f->end)
            rptr = f->buffer;
        buf_size -= len;
    }
    *rptr_ptr = rptr;
    return 0;
}

int filename_number_test(const char *filename)
{
    char buf[1024];
    if(!filename)
        return -1;
    return get_frame_filename(buf, sizeof(buf), filename, 1);
}

/* guess file format */
AVInputFormat *av_probe_input_format(AVProbeData *pd, int is_opened)
{
    AVInputFormat *fmt1, *fmt;
    int score, score_max;

    fmt = NULL;
    score_max = 0;
    for(fmt1 = first_iformat; fmt1 != NULL; fmt1 = fmt1->next) {
        if (!is_opened && !(fmt1->flags & AVFMT_NOFILE))
            continue;
        score = 0;
        if (fmt1->read_probe) {
            score = fmt1->read_probe(pd);
        } else if (fmt1->extensions) {
            if (match_ext(pd->filename, fmt1->extensions)) {
                score = 50;
            }
        } 
        if (score > score_max) {
            score_max = score;
            fmt = fmt1;
        }
    }
    return fmt;
}

/************************************************************/
/* input media file */

/**
 * open a media file from an IO stream. 'fmt' must be specified.
 */

static const char* format_to_name(void* ptr)
{
    AVFormatContext* fc = (AVFormatContext*) ptr;
    if(fc->iformat) return fc->iformat->name;
    else if(fc->oformat) return fc->oformat->name;
    else return "NULL";
}

static const AVClass av_format_context_class = { "AVFormatContext", format_to_name };

AVFormatContext *av_alloc_format_context(void)
{
    AVFormatContext *ic;
    ic = av_mallocz(sizeof(AVFormatContext));
    if (!ic) return ic;
    ic->av_class = &av_format_context_class;
    return ic;
}

int av_open_input_stream(AVFormatContext **ic_ptr, 
                         ByteIOContext *pb, const char *filename, 
                         AVInputFormat *fmt, AVFormatParameters *ap)
{
    int err;
    AVFormatContext *ic;

    ic = av_alloc_format_context();
    if (!ic) {
        err = AVERROR_NOMEM;
        goto fail;
    }
    ic->iformat = fmt;
    if (pb)
        ic->pb = *pb;
    ic->duration = AV_NOPTS_VALUE;
    ic->start_time = AV_NOPTS_VALUE;
    pstrcpy(ic->filename, sizeof(ic->filename), filename);

    /* allocate private data */
    if (fmt->priv_data_size > 0) {
        ic->priv_data = av_mallocz(fmt->priv_data_size);
        if (!ic->priv_data) {
            err = AVERROR_NOMEM;
            goto fail;
        }
    } else {
        ic->priv_data = NULL;
    }

    err = ic->iformat->read_header(ic, ap);
    if (err < 0)
        goto fail;

    if (pb)
        ic->data_offset = url_ftell(&ic->pb);

    *ic_ptr = ic;
    return 0;
 fail:
    if (ic) {
        av_freep(&ic->priv_data);
    }
    av_free(ic);
    *ic_ptr = NULL;
    return err;
}

#define PROBE_BUF_SIZE 2048

/**
 * Open a media file as input. The codec are not opened. Only the file
 * header (if present) is read.
 *
 * @param ic_ptr the opened media file handle is put here
 * @param filename filename to open.
 * @param fmt if non NULL, force the file format to use
 * @param buf_size optional buffer size (zero if default is OK)
 * @param ap additionnal parameters needed when opening the file (NULL if default)
 * @return 0 if OK. AVERROR_xxx otherwise.
 */
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;
    uint8_t buf[PROBE_BUF_SIZE];
    AVProbeData probe_data, *pd = &probe_data;
    ByteIOContext pb1, *pb = &pb1;
    
    file_opened = 0;
    pd->filename = "";
    if (filename)
        pd->filename = filename;
    pd->buf = buf;
    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 its uninitalized
    }

    if (!fmt || must_open_file) {
        /* if no file needed do not try to open one */
        if (url_fopen(pb, filename, URL_RDONLY) < 0) {
            err = AVERROR_IO;
            goto fail;
        }
        file_opened = 1;
        if (buf_size > 0) {
            url_setbufsize(pb, buf_size);
        }
        if (!fmt) {
            /* read probe data */
            pd->buf_size = get_buffer(pb, buf, PROBE_BUF_SIZE);
            if (url_fseek(pb, 0, SEEK_SET) == (offset_t)-EPIPE) {
                url_fclose(pb);
                if (url_fopen(pb, filename, URL_RDONLY) < 0) {
                    err = AVERROR_IO;
                    goto fail;
                }
            }
        }
    }
    
    /* guess file format */
    if (!fmt) {
        fmt = av_probe_input_format(pd, 1);
    }

    /* if still no format found, error */
    if (!fmt) {
        err = AVERROR_NOFMT;
        goto fail;
    }
        
    /* XXX: suppress this hack for redirectors */
#ifdef CONFIG_NETWORK
    if (fmt == &redir_demux) {
        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 (filename_number_test(filename) < 0) { 
            err = AVERROR_NUMEXPECTED;
            goto fail;
        }
    }
    err = av_open_input_stream(ic_ptr, pb, filename, fmt, ap);
    if (err)
        goto fail;
    return 0;
 fail:
    if (file_opened)
        url_fclose(pb);
    *ic_ptr = NULL;
    return err;
    
}

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

/**
 * Read a transport packet from a media file. This function is
 * absolete and should never be used. Use av_read_frame() instead.
 * 
 * @param s media file handle
 * @param pkt is filled 
 * @return 0 if OK. AVERROR_xxx if error.  
 */
int av_read_packet(AVFormatContext *s, AVPacket *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) {
        /* specific hack for pcm codecs because no frame size is
           provided */
        switch(enc->codec_id) {
        case CODEC_ID_PCM_S16LE:
        case CODEC_ID_PCM_S16BE:
        case CODEC_ID_PCM_U16LE:
        case CODEC_ID_PCM_U16BE:
            if (enc->channels == 0)
                return -1;
            frame_size = size / (2 * enc->channels);
            break;
        case CODEC_ID_PCM_S8:
        case CODEC_ID_PCM_U8:
        case CODEC_ID_PCM_MULAW:
        case CODEC_ID_PCM_ALAW:
            if (enc->channels == 0)
                return -1;
            frame_size = size / (enc->channels);
            break;
        default:
            /* used for example by ADPCM codecs */
            if (enc->bit_rate == 0)
                return -1;
            frame_size = (size * 8 * enc->sample_rate) / enc->bit_rate;
            break;
        }
    } 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:
        *pnum = st->codec.frame_rate_base;
        *pden = st->codec.frame_rate;
        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 int64_t lsb2full(int64_t lsb, int64_t last_ts, int lsb_bits){
    int64_t mask = lsb_bits < 64 ? (1LL<<lsb_bits)-1 : -1LL;
    int64_t delta= last_ts - mask/2;
    return  ((lsb - delta)&mask) + delta;
}

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

    /* handle wrapping */
    if(st->cur_dts != AV_NOPTS_VALUE){
        if(pkt->pts != AV_NOPTS_VALUE)
            pkt->pts= lsb2full(pkt->pts, st->cur_dts, st->pts_wrap_bits);
        if(pkt->dts != AV_NOPTS_VALUE)
            pkt->dts= lsb2full(pkt->dts, st->cur_dts, 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);
        }
    }

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

    /* do we have a video B frame ? */
    presentation_delayed = 0;
    if (st->codec.codec_type == CODEC_TYPE_VIDEO) {
        /* XXX: need has_b_frame, but cannot get it if the codec is
           not initialized */
        if ((   st->codec.codec_id == CODEC_ID_H264 
             || st->codec.has_b_frames) && 
            pc && pc->pict_type != FF_B_TYPE)
            presentation_delayed = 1;
        /* this may be redundant, but it shouldnt 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){
        if(presentation_delayed) st->cur_dts = -pkt->duration;
        else                     st->cur_dts = 0;
    }

//    av_log(NULL, AV_LOG_DEBUG, "IN delayed:%d pts:%lld, dts:%lld cur_dts:%lld 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 (presentation_delayed) {
        /* DTS = decompression time stamp */
        /* PTS = presentation time stamp */
        if (pkt->dts == AV_NOPTS_VALUE) {
            /* if we know the last pts, use it */
            if(st->last_IP_pts != AV_NOPTS_VALUE)
                st->cur_dts = pkt->dts = st->last_IP_pts;
            else
                pkt->dts = st->cur_dts;
        } else {
            st->cur_dts = pkt->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->cur_dts += pkt->duration;
        else
            st->cur_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 {
        /* presentation is not delayed : PTS and DTS are the same */
        if (pkt->pts == AV_NOPTS_VALUE) {
            if (pkt->dts == AV_NOPTS_VALUE) {
                pkt->pts = st->cur_dts;
                pkt->dts = st->cur_dts;
            }
            else {
                st->cur_dts = pkt->dts;
                pkt->pts = pkt->dts;
            }
        } else {
            st->cur_dts = pkt->pts;
            pkt->dts = pkt->pts;
        }
        st->cur_dts += pkt->duration;
    }
//    av_log(NULL, AV_LOG_DEBUG, "OUTdelayed:%d pts:%lld, dts:%lld cur_dts:%lld\n", presentation_delayed, pkt->pts, pkt->dts, st->cur_dts);
    
    /* update flags */
    if (pc) {
        pkt->flags = 0;
        /* key frame computation */
        switch(st->codec.codec_type) {
        case CODEC_TYPE_VIDEO:
            if (pc->pict_type == FF_I_TYPE)
                pkt->flags |= PKT_FLAG_KEY;
            break;
        case CODEC_TYPE_AUDIO:
            pkt->flags |= PKT_FLAG_KEY;
            break;
        default:
            break;
        }
    }

    /* convert the packet time stamp units */
    if(pkt->pts != AV_NOPTS_VALUE)
        pkt->pts = av_rescale(pkt->pts, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);
    if(pkt->dts != AV_NOPTS_VALUE)
        pkt->dts = av_rescale(pkt->dts, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);

    /* duration field */
    pkt->duration = av_rescale(pkt->duration, AV_TIME_BASE * (int64_t)st->time_base.num, st->time_base.den);
}

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->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) {
                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) {
                        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;
                }
            }
        }
    }
}

/**
 * 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;

    pktl = s->packet_buffer;
    if (pktl) {
        /* read packet from packet buffer, if there is data */
        *pkt = pktl->pkt;
        s->packet_buffer = pktl->next;
        av_free(pktl);
        return 0;
    } else {
        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 distance, int flags)
{
    AVIndexEntry *entries, *ie;
    int index;