C++ ff_start_tag函数代码示例

static int wav_write_header(AVFormatContext *s)
{
    WAVMuxContext *wav = s->priv_data;
    AVIOContext *pb = s->pb;
    int64_t fmt;

    if (wav->rf64 == RF64_ALWAYS) {
        ffio_wfourcc(pb, "RF64");
        avio_wl32(pb, -1); /* RF64 chunk size: use size in ds64 */
    } else {
        ffio_wfourcc(pb, "RIFF");
        avio_wl32(pb, 0); /* file length */
    }

    ffio_wfourcc(pb, "WAVE");

    if (wav->rf64 != RF64_NEVER) {
        /* write empty ds64 chunk or JUNK chunk to reserve space for ds64 */
        ffio_wfourcc(pb, wav->rf64 == RF64_ALWAYS ? "ds64" : "JUNK");
        avio_wl32(pb, 28); /* chunk size */
        wav->ds64 = avio_tell(pb);
        ffio_fill(pb, 0, 28);
    }

    /* format header */
    fmt = ff_start_tag(pb, "fmt ");
    if (ff_put_wav_header(pb, s->streams[0]->codec) < 0) {
        av_log(s, AV_LOG_ERROR, "%s codec not supported in WAVE format\n",
               s->streams[0]->codec->codec ? s->streams[0]->codec->codec->name : "NONE");
        return -1;
    }
    ff_end_tag(pb, fmt);

    if (s->streams[0]->codec->codec_tag != 0x01 /* hence for all other than PCM */
        && s->pb->seekable) {
        wav->fact_pos = ff_start_tag(pb, "fact");
        avio_wl32(pb, 0);
        ff_end_tag(pb, wav->fact_pos);
    }

    if (wav->write_bext)
        bwf_write_bext_chunk(s);

    avpriv_set_pts_info(s->streams[0], 64, 1, s->streams[0]->codec->sample_rate);
    wav->maxpts = wav->last_duration = 0;
    wav->minpts = INT64_MAX;

    /* info header */
    ff_riff_write_info(s);

    /* data header */
    wav->data = ff_start_tag(pb, "data");

    avio_flush(pb);

    return 0;
}

static int mmf_write_header(AVFormatContext *s)
{
    MMFContext *mmf = s->priv_data;
    AVIOContext *pb = s->pb;
    int64_t pos;
    int rate;

    rate = mmf_rate_code(s->streams[0]->codec->sample_rate);
    if (rate < 0) {
        av_log(s, AV_LOG_ERROR, "Unsupported sample rate %d\n",
               s->streams[0]->codec->sample_rate);
        return -1;
    }

    ffio_wfourcc(pb, "MMMD");
    avio_wb32(pb, 0);
    pos = ff_start_tag(pb, "CNTI");
    avio_w8(pb, 0); /* class */
    avio_w8(pb, 0); /* type */
    avio_w8(pb, 0); /* code type */
    avio_w8(pb, 0); /* status */
    avio_w8(pb, 0); /* counts */
    end_tag_be(pb, pos);

    pos = ff_start_tag(pb, "OPDA");
    avio_write(pb, "VN:libavcodec,", sizeof("VN:libavcodec,") -1); /* metadata ("ST:songtitle,VN:version,...") */
    end_tag_be(pb, pos);

    avio_write(pb, "ATR\x00", 4);
    avio_wb32(pb, 0);
    mmf->atrpos = avio_tell(pb);
    avio_w8(pb, 0); /* format type */
    avio_w8(pb, 0); /* sequence type */
    avio_w8(pb, (0 << 7) | (1 << 4) | rate); /* (channel << 7) | (format << 4) | rate */
    avio_w8(pb, 0); /* wave base bit */
    avio_w8(pb, 2); /* time base d */
    avio_w8(pb, 2); /* time base g */

    ffio_wfourcc(pb, "Atsq");
    avio_wb32(pb, 16);
    mmf->atsqpos = avio_tell(pb);
    /* Will be filled on close */
    avio_write(pb, "\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00", 16);

    mmf->awapos = ff_start_tag(pb, "Awa\x01");

    avpriv_set_pts_info(s->streams[0], 64, 1, s->streams[0]->codec->sample_rate);

    avio_flush(pb);

    return 0;
}

static void write_odml_master(AVFormatContext *s, int stream_index)
{
    AVIOContext *pb = s->pb;
    AVStream *st = s->streams[stream_index];
    AVCodecContext *enc = st->codec;
    AVIStream *avist = st->priv_data;
    unsigned char tag[5];
    int j;

    /* Starting to lay out AVI OpenDML master index.
        * We want to make it JUNK entry for now, since we'd
        * like to get away without making AVI an OpenDML one
        * for compatibility reasons. */
    avist->indexes.indx_start = ff_start_tag(pb, "JUNK");
    avio_wl16(pb, 4);   /* wLongsPerEntry */
    avio_w8(pb, 0);     /* bIndexSubType (0 == frame index) */
    avio_w8(pb, 0);     /* bIndexType (0 == AVI_INDEX_OF_INDEXES) */
    avio_wl32(pb, 0);   /* nEntriesInUse (will fill out later on) */
    ffio_wfourcc(pb, avi_stream2fourcc(tag, stream_index, enc->codec_type));
                        /* dwChunkId */
    avio_wl64(pb, 0);   /* dwReserved[3] */
    avio_wl32(pb, 0);   /* Must be 0.    */
    for (j = 0; j < AVI_MASTER_INDEX_SIZE * 2; j++)
        avio_wl64(pb, 0);
    ff_end_tag(pb, avist->indexes.indx_start);
}

static int64_t avi_start_new_riff(AVFormatContext *s, AVIOContext *pb,
                                  const char* riff_tag, const char* list_tag)
{
    AVIContext *avi= s->priv_data;
    int64_t loff;
    int i;

    avi->riff_id++;
    for (i=0; i<s->nb_streams; i++){
        AVIStream *avist= s->streams[i]->priv_data;
        avist->indexes.entry = 0;
    }

    avi->riff_start = ff_start_tag(pb, "RIFF");
    ffio_wfourcc(pb, riff_tag);
    loff = ff_start_tag(pb, "LIST");
    ffio_wfourcc(pb, list_tag);
    return loff;
}

static int wav_write_header(AVFormatContext *s)
{
    WAVMuxContext *wav = s->priv_data;
    AVIOContext *pb = s->pb;
    int64_t fmt;

    ffio_wfourcc(pb, "RIFF");
    avio_wl32(pb, 0); /* file length */
    ffio_wfourcc(pb, "WAVE");

    /* format header */
    fmt = ff_start_tag(pb, "fmt ");
    if (ff_put_wav_header(pb, s->streams[0]->codec) < 0) {
        av_log(s, AV_LOG_ERROR, "%s codec not supported in WAVE format\n",
               s->streams[0]->codec->codec ? s->streams[0]->codec->codec->name : "NONE");
        return -1;
    }
    ff_end_tag(pb, fmt);

    if (s->streams[0]->codec->codec_tag != 0x01 /* hence for all other than PCM */
            && s->pb->seekable) {
        wav->fact_pos = ff_start_tag(pb, "fact");
        avio_wl32(pb, 0);
        ff_end_tag(pb, wav->fact_pos);
    }

    if (wav->write_bext)
        bwf_write_bext_chunk(s);

    avpriv_set_pts_info(s->streams[0], 64, 1, s->streams[0]->codec->sample_rate);
    wav->maxpts = wav->last_duration = 0;
    wav->minpts = INT64_MAX;

    /* info header */
    ff_riff_write_info(s);

    /* data header */
    wav->data = ff_start_tag(pb, "data");

    avio_flush(pb);

    return 0;
}

static int wav_write_header(AVFormatContext *s)
{
    WAVContext *wav = s->priv_data;
    ByteIOContext *pb = s->pb;
    int64_t fmt, fact;

    put_tag(pb, "RIFF");
    put_le32(pb, 0); /* file length */
    put_tag(pb, "WAVE");

    /* format header */
    fmt = ff_start_tag(pb, "fmt ");
    if (ff_put_wav_header(pb, s->streams[0]->codec) < 0) {
        av_log(s, AV_LOG_ERROR, "%s codec not supported in WAVE format\n",
               s->streams[0]->codec->codec ? s->streams[0]->codec->codec->name : "NONE");
        av_free(wav);
        return -1;
    }
    ff_end_tag(pb, fmt);

    if (s->streams[0]->codec->codec_tag != 0x01 /* hence for all other than PCM */
        && !url_is_streamed(s->pb)) {
        fact = ff_start_tag(pb, "fact");
        put_le32(pb, 0);
        ff_end_tag(pb, fact);
    }

    av_set_pts_info(s->streams[0], 64, 1, s->streams[0]->codec->sample_rate);
    wav->maxpts = wav->last_duration = 0;
    wav->minpts = INT64_MAX;

    /* data header */
    wav->data = ff_start_tag(pb, "data");

    put_flush_packet(pb);

    return 0;
}

static int avi_write_idx1(AVFormatContext *s)
{
    AVIOContext *pb = s->pb;
    AVIContext *avi = s->priv_data;
    int64_t idx_chunk;
    int i;
    char tag[5];

    if (pb->seekable) {
        AVIStream *avist;
        AVIIentry* ie = 0, *tie;
        int empty, stream_id = -1;

        idx_chunk = ff_start_tag(pb, "idx1");
        for(i=0; i<s->nb_streams; i++){
            avist= s->streams[i]->priv_data;
            avist->entry=0;
        }

        do {
            empty = 1;
            for (i=0; i<s->nb_streams; i++) {
                avist= s->streams[i]->priv_data;
                 if (avist->indexes.entry <= avist->entry)
                     continue;

                 tie = avi_get_ientry(&avist->indexes, avist->entry);
                 if (empty || tie->pos < ie->pos) {
                     ie = tie;
                     stream_id = i;
                 }
                 empty = 0;
            }
            if (!empty) {
                avist= s->streams[stream_id]->priv_data;
                avi_stream2fourcc(tag, stream_id,
                                  s->streams[stream_id]->codec->codec_type);
                ffio_wfourcc(pb, tag);
                avio_wl32(pb, ie->flags);
                avio_wl32(pb, ie->pos);
                avio_wl32(pb, ie->len);
                avist->entry++;
            }
        } while (!empty);
        ff_end_tag(pb, idx_chunk);

        avi_write_counters(s, avi->riff_id);
    }
    return 0;
}

static int peak_write_chunk(AVFormatContext *s)
{
    WAVMuxContext *wav = s->priv_data;
    AVIOContext *pb = s->pb;
    AVCodecContext *enc = s->streams[0]->codec;
    int64_t peak = ff_start_tag(s->pb, "levl");
    int64_t now0;
    time_t now_secs;
    char timestamp[28];

    /* Peak frame of incomplete block at end */
    if (wav->peak_block_pos)
        peak_write_frame(s);

    memset(timestamp, 0, sizeof(timestamp));
    if (!(s->flags & AVFMT_FLAG_BITEXACT)) {
        struct tm tmpbuf;
        av_log(s, AV_LOG_INFO, "Writing local time and date to Peak Envelope Chunk\n");
        now0 = av_gettime();
        now_secs = now0 / 1000000;
        if (strftime(timestamp, sizeof(timestamp), "%Y:%m:%d:%H:%M:%S:", localtime_r(&now_secs, &tmpbuf))) {
            av_strlcatf(timestamp, sizeof(timestamp), "%03d", (int)((now0 / 1000) % 1000));
        } else {
            av_log(s, AV_LOG_ERROR, "Failed to write timestamp\n");
            return -1;
        }
    }

    avio_wl32(pb, 1);                           /* version */
    avio_wl32(pb, wav->peak_format);            /* 8 or 16 bit */
    avio_wl32(pb, wav->peak_ppv);               /* positive and negative */
    avio_wl32(pb, wav->peak_block_size);        /* frames per value */
    avio_wl32(pb, enc->channels);               /* number of channels */
    avio_wl32(pb, wav->peak_num_frames);        /* number of peak frames */
    avio_wl32(pb, wav->peak_pos_pop);           /* audio sample frame index */
    avio_wl32(pb, 128);                         /* equal to size of header */
    avio_write(pb, timestamp, 28);              /* ASCII time stamp */
    ffio_fill(pb, 0, 60);

    avio_write(pb, wav->peak_output, wav->peak_outbuf_bytes);

    ff_end_tag(pb, peak);

    if (!wav->data)
        wav->data = peak;

    return 0;
}

void ff_riff_write_info(AVFormatContext *s)
{
    AVIOContext *pb = s->pb;
    int i;
    int64_t list_pos;
    AVDictionaryEntry *t = NULL;

    ff_metadata_conv(&s->metadata, ff_riff_info_conv, NULL);

    /* writing empty LIST is not nice and may cause problems */
    if (!riff_has_valid_tags(s))
        return;

    list_pos = ff_start_tag(pb, "LIST");
    ffio_wfourcc(pb, "INFO");
    for (i = 0; *riff_tags[i]; i++)
        if ((t = av_dict_get(s->metadata, riff_tags[i],
                             NULL, AV_DICT_MATCH_CASE)))
            ff_riff_write_info_tag(s->pb, t->key, t->value);
    ff_end_tag(pb, list_pos);
}

static void bwf_write_bext_chunk(AVFormatContext *s)
{
    AVDictionaryEntry *tmp_tag;
    uint64_t time_reference = 0;
    int64_t bext = ff_start_tag(s->pb, "bext");

    bwf_write_bext_string(s, "description", 256);
    bwf_write_bext_string(s, "originator", 32);
    bwf_write_bext_string(s, "originator_reference", 32);
    bwf_write_bext_string(s, "origination_date", 10);
    bwf_write_bext_string(s, "origination_time", 8);

    if (tmp_tag = av_dict_get(s->metadata, "time_reference", NULL, 0))
        time_reference = strtoll(tmp_tag->value, NULL, 10);
    avio_wl64(s->pb, time_reference);
    avio_wl16(s->pb, 1);  // set version to 1

    if (tmp_tag = av_dict_get(s->metadata, "umid", NULL, 0)) {
        unsigned char umidpart_str[17] = {0};
        int i;
        uint64_t umidpart;
        int len = strlen(tmp_tag->value+2);

        for (i = 0; i < len/16; i++) {
            memcpy(umidpart_str, tmp_tag->value + 2 + (i*16), 16);
            umidpart = strtoll(umidpart_str, NULL, 16);
            avio_wb64(s->pb, umidpart);
        }
        ffio_fill(s->pb, 0, 64 - i*8);
    } else
        ffio_fill(s->pb, 0, 64); // zero UMID

    ffio_fill(s->pb, 0, 190); // Reserved

    if (tmp_tag = av_dict_get(s->metadata, "coding_history", NULL, 0))
        avio_put_str(s->pb, tmp_tag->value);

    ff_end_tag(s->pb, bext);
}

static int avi_write_header(AVFormatContext *s)
{
    AVIContext *avi = s->priv_data;
    AVIOContext *pb = s->pb;
    int bitrate, n, i, nb_frames, au_byterate, au_ssize, au_scale;
    AVCodecContext *stream, *video_enc;
    int64_t list1, list2, strh, strf;
    AVDictionaryEntry *t = NULL;

    if (s->nb_streams > AVI_MAX_STREAM_COUNT) {
        av_log(s, AV_LOG_ERROR, "AVI does not support >%d streams\n",
               AVI_MAX_STREAM_COUNT);
        return AVERROR(EINVAL);
    }

    for(n=0;n<s->nb_streams;n++) {
        s->streams[n]->priv_data= av_mallocz(sizeof(AVIStream));
        if(!s->streams[n]->priv_data)
            return AVERROR(ENOMEM);
    }

    /* header list */
    avi->riff_id = 0;
    list1 = avi_start_new_riff(s, pb, "AVI ", "hdrl");

    /* avi header */
    ffio_wfourcc(pb, "avih");
    avio_wl32(pb, 14 * 4);
    bitrate = 0;

    video_enc = NULL;
    for(n=0;n<s->nb_streams;n++) {
        stream = s->streams[n]->codec;
        bitrate += stream->bit_rate;
        if (stream->codec_type == AVMEDIA_TYPE_VIDEO)
            video_enc = stream;
    }

    nb_frames = 0;

    if(video_enc){
        avio_wl32(pb, (uint32_t)(INT64_C(1000000) * video_enc->time_base.num / video_enc->time_base.den));
    } else {
        avio_wl32(pb, 0);
    }
    avio_wl32(pb, bitrate / 8); /* XXX: not quite exact */
    avio_wl32(pb, 0); /* padding */
    if (!pb->seekable)
        avio_wl32(pb, AVIF_TRUSTCKTYPE | AVIF_ISINTERLEAVED); /* flags */
    else
        avio_wl32(pb, AVIF_TRUSTCKTYPE | AVIF_HASINDEX | AVIF_ISINTERLEAVED); /* flags */
    avi->frames_hdr_all = avio_tell(pb); /* remember this offset to fill later */
    avio_wl32(pb, nb_frames); /* nb frames, filled later */
    avio_wl32(pb, 0); /* initial frame */
    avio_wl32(pb, s->nb_streams); /* nb streams */
    avio_wl32(pb, 1024 * 1024); /* suggested buffer size */
    if(video_enc){
        avio_wl32(pb, video_enc->width);
        avio_wl32(pb, video_enc->height);
    } else {
        avio_wl32(pb, 0);
        avio_wl32(pb, 0);
    }
    avio_wl32(pb, 0); /* reserved */
    avio_wl32(pb, 0); /* reserved */
    avio_wl32(pb, 0); /* reserved */
    avio_wl32(pb, 0); /* reserved */

    /* stream list */
    for(i=0;i<n;i++) {
        AVIStream *avist= s->streams[i]->priv_data;
        list2 = ff_start_tag(pb, "LIST");
        ffio_wfourcc(pb, "strl");

        stream = s->streams[i]->codec;

        /* stream generic header */
        strh = ff_start_tag(pb, "strh");
        switch(stream->codec_type) {
        case AVMEDIA_TYPE_SUBTITLE:
            // XSUB subtitles behave like video tracks, other subtitles
            // are not (yet) supported.
            if (stream->codec_id != AV_CODEC_ID_XSUB) {
                av_log(s, AV_LOG_ERROR, "Subtitle streams other than DivX XSUB are not supported by the AVI muxer.\n");
                return AVERROR_PATCHWELCOME;
            }
        case AVMEDIA_TYPE_VIDEO: ffio_wfourcc(pb, "vids"); break;
        case AVMEDIA_TYPE_AUDIO: ffio_wfourcc(pb, "auds"); break;
//      case AVMEDIA_TYPE_TEXT : ffio_wfourcc(pb, "txts"); break;
        case AVMEDIA_TYPE_DATA : ffio_wfourcc(pb, "dats"); break;
        }
        if(stream->codec_type == AVMEDIA_TYPE_VIDEO ||
           stream->codec_id == AV_CODEC_ID_XSUB)
            avio_wl32(pb, stream->codec_tag);
        else
            avio_wl32(pb, 1);
        avio_wl32(pb, 0); /* flags */
        avio_wl16(pb, 0); /* priority */
        avio_wl16(pb, 0); /* language */
        avio_wl32(pb, 0); /* initial frame */
//.........这里部分代码省略.........

static int wav_write_header(AVFormatContext *s)
{
    WAVMuxContext *wav = s->priv_data;
    AVIOContext *pb = s->pb;
    int64_t fmt;

    if (s->nb_streams != 1) {
        av_log(s, AV_LOG_ERROR, "WAVE files have exactly one stream\n");
        return AVERROR(EINVAL);
    }

    if (wav->rf64 == RF64_ALWAYS) {
        ffio_wfourcc(pb, "RF64");
        avio_wl32(pb, -1); /* RF64 chunk size: use size in ds64 */
    } else {
        ffio_wfourcc(pb, "RIFF");
        avio_wl32(pb, -1); /* file length */
    }

    ffio_wfourcc(pb, "WAVE");

    if (wav->rf64 != RF64_NEVER) {
        /* write empty ds64 chunk or JUNK chunk to reserve space for ds64 */
        ffio_wfourcc(pb, wav->rf64 == RF64_ALWAYS ? "ds64" : "JUNK");
        avio_wl32(pb, 28); /* chunk size */
        wav->ds64 = avio_tell(pb);
        ffio_fill(pb, 0, 28);
    }

    if (wav->write_peak != 2) {
        /* format header */
        fmt = ff_start_tag(pb, "fmt ");
        if (ff_put_wav_header(pb, s->streams[0]->codec, 0) < 0) {
            const AVCodecDescriptor *desc = avcodec_descriptor_get(s->streams[0]->codec->codec_id);
            av_log(s, AV_LOG_ERROR, "%s codec not supported in WAVE format\n",
                   desc ? desc->name : "unknown");
            return AVERROR(ENOSYS);
        }
        ff_end_tag(pb, fmt);
    }

    if (s->streams[0]->codec->codec_tag != 0x01 /* hence for all other than PCM */
        && s->pb->seekable) {
        wav->fact_pos = ff_start_tag(pb, "fact");
        avio_wl32(pb, 0);
        ff_end_tag(pb, wav->fact_pos);
    }

    if (wav->write_bext)
        bwf_write_bext_chunk(s);

    if (wav->write_peak) {
        int ret;
        if ((ret = peak_init_writer(s)) < 0)
            return ret;
    }

    avpriv_set_pts_info(s->streams[0], 64, 1, s->streams[0]->codec->sample_rate);
    wav->maxpts = wav->last_duration = 0;
    wav->minpts = INT64_MAX;

    if (wav->write_peak != 2) {
        /* info header */
        ff_riff_write_info(s);

        /* data header */
        wav->data = ff_start_tag(pb, "data");
    }

    avio_flush(pb);

    return 0;
}

static int avi_write_header(AVFormatContext *s)
{
    AVIContext *avi = s->priv_data;
    AVIOContext *pb = s->pb;
    int bitrate, n, i, nb_frames, au_byterate, au_ssize, au_scale;
    AVCodecContext *video_enc;
    AVStream *video_st = NULL;
    int64_t list1, list2, strh, strf;
    AVDictionaryEntry *t = NULL;
    int padding;

    if (s->nb_streams > AVI_MAX_STREAM_COUNT) {
        av_log(s, AV_LOG_ERROR, "AVI does not support >%d streams\n",
               AVI_MAX_STREAM_COUNT);
        return AVERROR(EINVAL);
    }

    for (n = 0; n < s->nb_streams; n++) {
        s->streams[n]->priv_data = av_mallocz(sizeof(AVIStream));
        if (!s->streams[n]->priv_data)
            return AVERROR(ENOMEM);
    }

    /* header list */
    avi->riff_id = 0;
    list1 = avi_start_new_riff(s, pb, "AVI ", "hdrl");

    /* avi header */
    ffio_wfourcc(pb, "avih");
    avio_wl32(pb, 14 * 4);
    bitrate = 0;

    video_enc = NULL;
    for (n = 0; n < s->nb_streams; n++) {
        AVCodecContext *codec = s->streams[n]->codec;
        bitrate += codec->bit_rate;
        if (codec->codec_type == AVMEDIA_TYPE_VIDEO) {
            video_enc = codec;
            video_st = s->streams[n];
        }
    }

    nb_frames = 0;

    // TODO: should be avg_frame_rate
    if (video_st)
        avio_wl32(pb, (uint32_t) (INT64_C(1000000) * video_st->time_base.num /
                                  video_st->time_base.den));
    else
        avio_wl32(pb, 0);
    avio_wl32(pb, bitrate / 8); /* XXX: not quite exact */
    avio_wl32(pb, 0); /* padding */
    if (!pb->seekable)
        avio_wl32(pb, AVIF_TRUSTCKTYPE | AVIF_ISINTERLEAVED);  /* flags */
    else
        avio_wl32(pb, AVIF_TRUSTCKTYPE | AVIF_HASINDEX | AVIF_ISINTERLEAVED);  /* flags */
    avi->frames_hdr_all = avio_tell(pb); /* remember this offset to fill later */
    avio_wl32(pb, nb_frames); /* nb frames, filled later */
    avio_wl32(pb, 0); /* initial frame */
    avio_wl32(pb, s->nb_streams); /* nb streams */
    avio_wl32(pb, 1024 * 1024); /* suggested buffer size */
    if (video_enc) {
        avio_wl32(pb, video_enc->width);
        avio_wl32(pb, video_enc->height);
    } else {
        avio_wl32(pb, 0);
        avio_wl32(pb, 0);
    }
    avio_wl32(pb, 0); /* reserved */
    avio_wl32(pb, 0); /* reserved */
    avio_wl32(pb, 0); /* reserved */
    avio_wl32(pb, 0); /* reserved */

    /* stream list */
    for (i = 0; i < n; i++) {
        AVStream *st = s->streams[i];
        AVCodecContext *enc = st->codec;
        AVIStream *avist = st->priv_data;
        list2 = ff_start_tag(pb, "LIST");
        ffio_wfourcc(pb, "strl");

        /* stream generic header */
        strh = ff_start_tag(pb, "strh");
        switch (enc->codec_type) {
        case AVMEDIA_TYPE_SUBTITLE:
            // XSUB subtitles behave like video tracks, other subtitles
            // are not (yet) supported.
            if (enc->codec_id != AV_CODEC_ID_XSUB) {
                av_log(s, AV_LOG_ERROR,
                       "Subtitle streams other than DivX XSUB are not supported by the AVI muxer.\n");
                return AVERROR_PATCHWELCOME;
            }
        case AVMEDIA_TYPE_VIDEO:
            ffio_wfourcc(pb, "vids");
            break;
        case AVMEDIA_TYPE_AUDIO:
            ffio_wfourcc(pb, "auds");
            break;
//      case AVMEDIA_TYPE_TEXT:
//          ffio_wfourcc(pb, "txts");
//.........这里部分代码省略.........