int64_t pts_inc;
static int fourxm_read_packet(AVFormatContext *s,                              AVPacket *pkt){    FourxmDemuxContext *fourxm = s->priv_data;    ByteIOContext *pb = &s->pb;    unsigned int fourcc_tag;    unsigned int size, out_size;    int ret = 0;    int track_number;    int packet_read = 0;    unsigned char header[8];    int64_t pts_inc;    int audio_frame_count;    while (!packet_read) {        if ((ret = get_buffer(&s->pb, header, 8)) < 0)            return ret;        fourcc_tag = LE_32(&header[0]);        size = LE_32(&header[4]);        if (url_feof(pb))            return AVERROR_IO;        switch (fourcc_tag) {        case LIST_TAG:            /* this is a good time to bump the video pts */            fourxm->video_pts += fourxm->video_pts_inc;            /* skip the LIST-* tag and move on to the next fourcc */            get_le32(pb);            break;        case ifrm_TAG:        case pfrm_TAG:        case cfrm_TAG:{            /* allocate 8 more bytes than 'size' to account for fourcc             * and size */            if (size + 8 < size || av_new_packet(pkt, size + 8))                return AVERROR_IO;            pkt->stream_index = fourxm->video_stream_index;            pkt->pts = fourxm->video_pts;            memcpy(pkt->data, header, 8);            ret = get_buffer(&s->pb, &pkt->data[8], size);            if (ret < 0)                av_free_packet(pkt);            else                packet_read = 1;            break;        }        case snd__TAG:            track_number = get_le32(pb);            out_size= get_le32(pb);            size-=8;            if (track_number == fourxm->selected_track) {                if (av_new_packet(pkt, size))                    return AVERROR_IO;                pkt->stream_index =                     fourxm->tracks[fourxm->selected_track].stream_index;                pkt->pts = fourxm->audio_pts;                ret = get_buffer(&s->pb, pkt->data, size);                if (ret < 0)                    av_free_packet(pkt);                else                    packet_read = 1;                /* pts accounting */                audio_frame_count = size;                if (fourxm->tracks[fourxm->selected_track].adpcm)                    audio_frame_count -=                         2 * (fourxm->tracks[fourxm->selected_track].channels);                audio_frame_count /=                      fourxm->tracks[fourxm->selected_track].channels;                if (fourxm->tracks[fourxm->selected_track].adpcm)                    audio_frame_count *= 2;                else                     audio_frame_count /=                    (fourxm->tracks[fourxm->selected_track].bits / 8);                pts_inc = audio_frame_count;                pts_inc *= 90000;                pts_inc /= fourxm->tracks[fourxm->selected_track].sample_rate;                fourxm->audio_pts += pts_inc;            } else {                url_fseek(pb, size, SEEK_CUR);            }            break;        default:            url_fseek(pb, size, SEEK_CUR);            break;        }    }    return ret;}