[Ffmpeg-devel] Re: [PATCH] seeking in GXF

[Michael Niedermayer]

Hi

On Mon, Jul 31, 2006 at 05:44:47PM +0200, Reimar D?ffinger wrote:
[...]
> +static void gxf_material_tags(ByteIOContext *pb, int *len, st_info_t *si) {
> +    while (*len >= 2) {
> +        mat_tag_t tag = get_byte(pb);
> +        int tlen = get_byte(pb);
> +        *len -= 2;
> +        if (tlen > *len)
> +            return;
> +        *len -= tlen;
> +        switch (tag) {
> +            case MAT_FIRST_FIELD:
> +                if (tlen != 4)
> +                    break;
> +                si->first_field = get_be32(pb);
> +                tlen = 0;
> +                break;
> +            case MAT_LAST_FIELD:
> +                if (tlen != 4)
> +                    break;
> +                si->last_field = get_be32(pb);
> +                tlen = 0;
> +                break;
> +        }
> +        url_fskip(pb, tlen);
> +    }
> +}

somehow i think this is more complex then really needed ...


> +
> +/**
> + * \brief convert fps tag value to AVRational fps
> + * \param fps fps value from tag
> + * \return fps as AVRational, or 0 / 0 if unknown
> + */
> +static AVRational fps_tag2avr(int32_t fps) {
> +    static const AVRational map[] = {{0, 0}, {60, 1}, {60000, 1001}, {50, 1},
> +        {30, 1}, {30000, 1001}, {25, 1}, {24, 1}, {24000, 1001}};

ff_frame_rate_tab[] in mpeg12data.h


> +    if (fps < 0 || fps > 8) fps = 0;
> +    return map[fps];
> +}
> +
> +/**
> + * \brief convert UMF attributes flags to AVRational fps
> + * \param fps fps value from flags
> + * \return fps as AVRational, or 0 / 0 if unknown
> + */
> +static AVRational fps_umf2avr(uint32_t flags) {
> +    static const AVRational map[] = {{50, 1}, {60000, 1001}, {24, 1},
> +        {25, 1}, {30000, 1001}};
> +    int idx =  ff_log2_tab[(flags & 0x7c0) >> 6];

why dont you use av_log2() ?


[...]


> +
> +/**
> + * \brief read index from FLT packet into stream 0 av_index
> + */
> +static void gxf_read_index(AVFormatContext *s, int pkt_len) {
> +    ByteIOContext *pb = &s->pb;
> +    AVStream *st = s->streams[0];
> +    uint32_t fields_per_map = get_le32(pb);
> +    uint32_t map_cnt = get_le32(pb);
> +    int i;
> +    pkt_len -= 8;
> +    if (map_cnt > 1000) {
> +        av_log(s, AV_LOG_ERROR, "GXF: too many index entries %u (%x)\n", map_cnt, map_cnt);
> +        map_cnt = 1000;
> +    }
> +    if (pkt_len < 4 * map_cnt) {
> +        av_log(s, AV_LOG_ERROR, "GXF: invalid index length\n");
> +        url_fskip(pb, pkt_len);
> +        return;
> +    }
> +    pkt_len -= 4 * map_cnt;
> +    av_add_index_entry(st, 0, 0, 0, 0, 0);
> +    for (i = 0; i < map_cnt; i++)
> +        av_add_index_entry(st, get_le32(pb) * 1024, i * fields_per_map + 1, 0, 0, 0);

the multiplications are int and will overflow


[...]
> +static int gxf_seek(AVFormatContext *s, int stream_index, int64_t timestamp, int flags) {
> +    uint64_t pos;
> +    uint64_t maxlen = 100 * 1024 * 1024;
> +    AVStream *st = s->streams[0];
> +    int64_t start_time = s->streams[stream_index]->start_time;
> +    int idx;
> +    if (timestamp < start_time) timestamp = start_time;
> +    idx = av_index_search_timestamp(st, timestamp - start_time,
> +                                    AVSEEK_FLAG_ANY | AVSEEK_FLAG_BACKWARD);
> +    if (idx < 0)
> +        return -1;
> +    pos = st->index_entries[idx].pos;
> +    if (idx < st->nb_index_entries - 2)
> +        maxlen = st->index_entries[idx + 2].pos - pos;
> +    if (maxlen < 200 * 1024) maxlen = 200 * 1024;

FFMAX()

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

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