FFmpeg/libavformat/assdec.c

/*
 * SSA/ASS demuxer
 * Copyright (c) 2008 Michael Niedermayer
 *
 * This file is part of Libav.
 *
 * Libav 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 2.1 of the License, or (at your option) any later version.
 *
 * Libav 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 Libav; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */

#include <stdint.h>

#include "libavutil/mathematics.h"

#include "avformat.h"
#include "internal.h"

#define MAX_LINESIZE 2000

typedef struct ASSContext {
    uint8_t *event_buffer;
    uint8_t **event;
    unsigned int event_count;
    unsigned int event_index;
} ASSContext;

static int probe(AVProbeData *p)
{
    const char *header = "[Script Info]";

    if (!memcmp(p->buf, header, strlen(header)) ||
        !memcmp(p->buf + 3, header, strlen(header)))
        return AVPROBE_SCORE_MAX;

    return 0;
}

static int read_close(AVFormatContext *s)
{
    ASSContext *ass = s->priv_data;

    av_freep(&ass->event_buffer);
    av_freep(&ass->event);

    return 0;
}

static int64_t get_pts(const uint8_t *p)
{
    int hour, min, sec, hsec;

    if (sscanf(p, "%*[^,],%d:%d:%d%*c%d", &hour, &min, &sec, &hsec) != 4)
        return AV_NOPTS_VALUE;

    av_log(NULL, AV_LOG_TRACE, "%d %d %d %d [%s]\n", hour, min, sec, hsec, p);

    min += 60 * hour;
    sec += 60 * min;

    return sec * 100 + hsec;
}

static int event_cmp(const void *_a, const void *_b)
{
    const uint8_t *const *a = _a, *const *b = _b;
    return get_pts(*a) - get_pts(*b);
}

static int read_header(AVFormatContext *s)
{
    int i, len, header_remaining;
    ASSContext *ass = s->priv_data;
    AVIOContext *pb = s->pb;
    AVStream *st;
    int allocated[2] = { 0 };
    uint8_t *p, **dst[2] = { 0 };
    int pos[2] = { 0 };

    st = avformat_new_stream(s, NULL);
    if (!st)
        return -1;
    avpriv_set_pts_info(st, 64, 1, 100);
    st->codecpar->codec_type = AVMEDIA_TYPE_SUBTITLE;
    st->codecpar->codec_id   = AV_CODEC_ID_SSA;

    header_remaining = INT_MAX;
    dst[0] = &st->codecpar->extradata;
    dst[1] = &ass->event_buffer;
    while (!pb->eof_reached) {
        uint8_t line[MAX_LINESIZE];

        len = ff_get_line(pb, line, sizeof(line));

        if (!memcmp(line, "[Events]", 8))
            header_remaining = 2;
        else if (line[0] == '[')
            header_remaining = INT_MAX;

        i = header_remaining == 0;

        if (i && get_pts(line) == AV_NOPTS_VALUE)
            continue;

        p = av_fast_realloc(*(dst[i]), &allocated[i], pos[i] + MAX_LINESIZE);
        if (!p)
            goto fail;
        *(dst[i]) = p;
        memcpy(p + pos[i], line, len + 1);
        pos[i] += len;
        if (i)
            ass->event_count++;
        else
            header_remaining--;
    }
    st->codecpar->extradata_size = pos[0];

    if (ass->event_count >= UINT_MAX / sizeof(*ass->event))
        goto fail;

    ass->event = av_malloc(ass->event_count * sizeof(*ass->event));
    p = ass->event_buffer;
    for (i = 0; i < ass->event_count; i++) {
        ass->event[i] = p;
        while (*p && *p != '\n')
            p++;
        p++;
    }

    qsort(ass->event, ass->event_count, sizeof(*ass->event), event_cmp);

    return 0;

fail:
    read_close(s);

    return -1;
}

static int read_packet(AVFormatContext *s, AVPacket *pkt)
{
    ASSContext *ass = s->priv_data;
    uint8_t *p, *end;
    int ret;

    if (ass->event_index >= ass->event_count)
        return AVERROR(EIO);

    p = ass->event[ass->event_index];

    end = strchr(p, '\n');
    ret = av_new_packet(pkt, end ? end - p + 1 : strlen(p));
    if (ret < 0)
        return ret;
    pkt->flags |= AV_PKT_FLAG_KEY;
    pkt->pos    = p - ass->event_buffer + s->streams[0]->codecpar->extradata_size;
    pkt->pts    = pkt->dts = get_pts(p);
    memcpy(pkt->data, p, pkt->size);

    ass->event_index++;

    return 0;
}

static int read_seek2(AVFormatContext *s, int stream_index,
                      int64_t min_ts, int64_t ts, int64_t max_ts, int flags)
{
    ASSContext *ass = s->priv_data;

    if (flags & AVSEEK_FLAG_BYTE) {
        return AVERROR(ENOSYS);
    } else if (flags & AVSEEK_FLAG_FRAME) {
        if (ts < 0 || ts >= ass->event_count)
            return AVERROR(ERANGE);
        ass->event_index = ts;
    } else {
        int i, idx = -1;
        int64_t min_ts_diff = INT64_MAX;
        if (stream_index == -1) {
            AVRational time_base = s->streams[0]->time_base;
            ts     = av_rescale_q(ts, AV_TIME_BASE_Q, time_base);
            min_ts = av_rescale_rnd(min_ts, time_base.den,
                                    time_base.num * (int64_t) AV_TIME_BASE,
                                    AV_ROUND_UP);
            max_ts = av_rescale_rnd(max_ts, time_base.den,
                                    time_base.num * (int64_t) AV_TIME_BASE,
                                    AV_ROUND_DOWN);
        }
        /* TODO: ass->event[] is sorted by pts so we could do a binary search */
        for (i = 0; i < ass->event_count; i++) {
            int64_t pts     = get_pts(ass->event[i]);
            int64_t ts_diff = FFABS(pts - ts);
            if (pts >= min_ts && pts <= max_ts && ts_diff < min_ts_diff) {
                min_ts_diff = ts_diff;
                idx         = i;
            }
        }
        if (idx < 0)
            return AVERROR(ERANGE);
        ass->event_index = idx;
    }
    return 0;
}

AVInputFormat ff_ass_demuxer = {
    .name           = "ass",
    .long_name      = NULL_IF_CONFIG_SMALL("SSA (SubStation Alpha) subtitle"),
    .priv_data_size = sizeof(ASSContext),
    .read_probe     = probe,
    .read_header    = read_header,
    .read_packet    = read_packet,
    .read_close     = read_close,
    .read_seek2     = read_seek2,
};