movtextdec.c

Go to the documentation of this file.

/*
 * 3GPP TS 26.245 Timed Text decoder
 * Copyright (c) 2012  Philip Langdale <philipl@overt.org>
 *
 * This file is part of FFmpeg.
 *
 * FFmpeg 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.
 *
 * FFmpeg 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 FFmpeg; if not, write to the Free Software
 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
 */
 
#include "avcodec.h"
#include "ass.h"
#include "libavutil/opt.h"
#include "libavutil/avstring.h"
#include "libavutil/common.h"
#include "libavutil/bprint.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/mem.h"
#include "bytestream.h"
#include "codec_internal.h"
 
#define STYLE_FLAG_BOLD         (1<<0)
#define STYLE_FLAG_ITALIC       (1<<1)
#define STYLE_FLAG_UNDERLINE    (1<<2)
 
#define BOX_SIZE_INITIAL    40
 
#define STYL_BOX   (1<<0)
#define HLIT_BOX   (1<<1)
#define HCLR_BOX   (1<<2)
#define TWRP_BOX   (1<<3)
 
#define BOTTOM_LEFT     1
#define BOTTOM_CENTER   2
#define BOTTOM_RIGHT    3
#define MIDDLE_LEFT     4
#define MIDDLE_CENTER   5
#define MIDDLE_RIGHT    6
#define TOP_LEFT        7
#define TOP_CENTER      8
#define TOP_RIGHT       9
 
#define RGB_TO_BGR(c) (((c) & 0xff) << 16 | ((c) & 0xff00) | (((c) >> 16) & 0xff))
 
typedef struct {
    uint16_t font_id;
    char *font;
} FontRecord;
 
typedef struct {
    uint16_t start;
    uint16_t end;
    uint8_t flags;
    uint8_t bold;
    uint8_t italic;
    uint8_t underline;
    int color;
    uint8_t alpha;
    uint8_t fontsize;
    uint16_t font_id;
} StyleBox;
 
typedef struct {
    StyleBox style;
    const char *font;
    int back_color;
    uint8_t back_alpha;
    int alignment;
} MovTextDefault;
 
typedef struct {
    uint16_t hlit_start;
    uint16_t hlit_end;
} HighlightBox;
 
typedef struct {
   uint8_t hlit_color[4];
} HilightcolorBox;
 
typedef struct {
    uint8_t wrap_flag;
} TextWrapBox;
 
typedef struct {
    AVClass *class;
    StyleBox *s;
    HighlightBox h;
    HilightcolorBox c;
    FontRecord *ftab;
    TextWrapBox w;
    MovTextDefault d;
    uint8_t box_flags;
    uint16_t style_entries, ftab_entries;
    int readorder;
    int frame_width;
    int frame_height;
} MovTextContext;
 
typedef struct {
    uint32_t type;
    unsigned base_size;
    int (*decode)(const uint8_t *tsmb, MovTextContext *m, uint64_t size);
} Box;
 
static void mov_text_cleanup(MovTextContext *m)
{
    if (m->box_flags & STYL_BOX) {
        av_freep(&m->s);
        m->style_entries = 0;
    }
}
 
static void mov_text_cleanup_ftab(MovTextContext *m)
{
    for (unsigned i = 0; i < m->ftab_entries; i++)
        av_freep(&m->ftab[i].font);
    av_freep(&m->ftab);
    m->ftab_entries = 0;
}
 
static void mov_text_parse_style_record(StyleBox *style, const uint8_t **ptr)
{
    // fontID
    style->font_id   = bytestream_get_be16(ptr);
    // face-style-flags
    style->flags     = bytestream_get_byte(ptr);
    style->bold      = !!(style->flags & STYLE_FLAG_BOLD);
    style->italic    = !!(style->flags & STYLE_FLAG_ITALIC);
    style->underline = !!(style->flags & STYLE_FLAG_UNDERLINE);
    // fontsize
    style->fontsize  = bytestream_get_byte(ptr);
    // Primary color
    style->color     = bytestream_get_be24(ptr);
    style->color     = RGB_TO_BGR(style->color);
    style->alpha     = bytestream_get_byte(ptr);
}
 
static int mov_text_tx3g(AVCodecContext *avctx, MovTextContext *m)
{
    const uint8_t *tx3g_ptr = avctx->extradata;
    int i, j = -1, font_length, remaining = avctx->extradata_size - BOX_SIZE_INITIAL;
    int8_t v_align, h_align;
    unsigned ftab_entries;
 
    m->ftab_entries = 0;
    if (remaining < 0)
        return -1;
 
    // Display Flags
    tx3g_ptr += 4;
    // Alignment
    h_align = bytestream_get_byte(&tx3g_ptr);
    v_align = bytestream_get_byte(&tx3g_ptr);
    if (h_align == 0) {
        if (v_align == 0)
            m->d.alignment = TOP_LEFT;
        if (v_align == 1)
            m->d.alignment = MIDDLE_LEFT;
        if (v_align == -1)
            m->d.alignment = BOTTOM_LEFT;
    }
    if (h_align == 1) {
        if (v_align == 0)
            m->d.alignment = TOP_CENTER;
        if (v_align == 1)
            m->d.alignment = MIDDLE_CENTER;
        if (v_align == -1)
            m->d.alignment = BOTTOM_CENTER;
    }
    if (h_align == -1) {
        if (v_align == 0)
            m->d.alignment = TOP_RIGHT;
        if (v_align == 1)
            m->d.alignment = MIDDLE_RIGHT;
        if (v_align == -1)
            m->d.alignment = BOTTOM_RIGHT;
    }
    // Background Color
    m->d.back_color = bytestream_get_be24(&tx3g_ptr);
    m->d.back_color = RGB_TO_BGR(m->d.back_color);
    m->d.back_alpha = bytestream_get_byte(&tx3g_ptr);
    // BoxRecord
    tx3g_ptr += 8;
    // StyleRecord
    tx3g_ptr += 4;
    mov_text_parse_style_record(&m->d.style, &tx3g_ptr);
    // FontRecord
    // FontRecord Size
    tx3g_ptr += 4;
    // ftab
    tx3g_ptr += 4;
 
    // In case of broken header, init default font
    m->d.font = ASS_DEFAULT_FONT;
 
    ftab_entries = bytestream_get_be16(&tx3g_ptr);
    if (!ftab_entries)
        return 0;
    remaining   -= 3 * ftab_entries;
    if (remaining < 0)
        return AVERROR_INVALIDDATA;
    m->ftab = av_calloc(ftab_entries, sizeof(*m->ftab));
    if (!m->ftab)
        return AVERROR(ENOMEM);
    m->ftab_entries = ftab_entries;
 
    for (i = 0; i < m->ftab_entries; i++) {
        m->ftab[i].font_id = bytestream_get_be16(&tx3g_ptr);
        if (m->ftab[i].font_id == m->d.style.font_id)
            j = i;
        font_length = bytestream_get_byte(&tx3g_ptr);
 
        remaining  -= font_length;
        if (remaining < 0) {
            mov_text_cleanup_ftab(m);
            return -1;
        }
        m->ftab[i].font = av_malloc(font_length + 1);
        if (!m->ftab[i].font) {
            mov_text_cleanup_ftab(m);
            return AVERROR(ENOMEM);
        }
        bytestream_get_buffer(&tx3g_ptr, m->ftab[i].font, font_length);
        m->ftab[i].font[font_length] = '\0';
    }
    if (j >= 0)
        m->d.font = m->ftab[j].font;
    return 0;
}
 
static int decode_twrp(const uint8_t *tsmb, MovTextContext *m, uint64_t size)
{
    m->box_flags |= TWRP_BOX;
    m->w.wrap_flag = bytestream_get_byte(&tsmb);
    return 0;
}
 
static int decode_hlit(const uint8_t *tsmb, MovTextContext *m, uint64_t size)
{
    m->box_flags |= HLIT_BOX;
    m->h.hlit_start = bytestream_get_be16(&tsmb);
    m->h.hlit_end   = bytestream_get_be16(&tsmb);
    return 0;
}
 
static int decode_hclr(const uint8_t *tsmb, MovTextContext *m, uint64_t size)
{
    m->box_flags |= HCLR_BOX;
    bytestream_get_buffer(&tsmb, m->c.hlit_color, 4);
    return 0;
}
 
static int styles_equivalent(const StyleBox *a, const StyleBox *b)
{
#define CMP(field) ((a)->field == (b)->field)
    return CMP(bold)  && CMP(italic)   && CMP(underline) && CMP(color) &&
           CMP(alpha) && CMP(fontsize) && CMP(font_id);
#undef CMP
}
 
static int decode_styl(const uint8_t *tsmb, MovTextContext *m, uint64_t size)
{
    int i;
    int style_entries = bytestream_get_be16(&tsmb);
    StyleBox *tmp;
 
    // A single style record is of length 12 bytes.
    if (2 + style_entries * 12 > size)
        return -1;
 
    tmp = av_realloc_array(m->s, style_entries, sizeof(*m->s));
    if (!tmp)
        return AVERROR(ENOMEM);
    m->s             = tmp;
    m->style_entries = style_entries;
 
    m->box_flags |= STYL_BOX;
    for(i = 0; i < m->style_entries; i++) {
        StyleBox *style = &m->s[i];
 
        style->start = bytestream_get_be16(&tsmb);
        style->end   = bytestream_get_be16(&tsmb);
        if (style->end < style->start ||
            (i && style->start < m->s[i - 1].end)) {
            mov_text_cleanup(m);
            return AVERROR_INVALIDDATA;
        }
        if (style->start == style->end) {
            /* Skip this style as it applies to no character */
            tsmb += 8;
            m->style_entries--;
            i--;
            continue;
        }
 
        mov_text_parse_style_record(style, &tsmb);
        if (styles_equivalent(style, &m->d.style)) {
            /* Skip this style as it is equivalent to the default style */
            m->style_entries--;
            i--;
            continue;
        } else if (i && style->start == style[-1].end &&
                   styles_equivalent(style, &style[-1])) {
            /* Merge the two adjacent styles */
            style[-1].end = style->end;
            m->style_entries--;
            i--;
            continue;
        }
    }
    return 0;
}
 
static const Box box_types[] = {
    { MKBETAG('s','t','y','l'), 2, decode_styl },
    { MKBETAG('h','l','i','t'), 4, decode_hlit },
    { MKBETAG('h','c','l','r'), 4, decode_hclr },
    { MKBETAG('t','w','r','p'), 1, decode_twrp }
};
 
const static size_t box_count = FF_ARRAY_ELEMS(box_types);
 
// Return byte length of the UTF-8 sequence starting at text[0]. 0 on error.
static int get_utf8_length_at(const char *text, const char *text_end)
{
    const char *start = text;
    int err = 0;
    uint32_t c;
    GET_UTF8(c, text < text_end ? (uint8_t)*text++ : (err = 1, 0), goto error;);
    if (err)
        goto error;
    return text - start;
error:
    return 0;
}
 
static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end,
                       AVCodecContext *avctx)
{
    MovTextContext *m = avctx->priv_data;
    const StyleBox *const default_style = &m->d.style;
    int i = 0;
    int text_pos = 0;
    int entry = 0;
    int color = default_style->color;
 
    if (text < text_end && m->box_flags & TWRP_BOX) {
        if (m->w.wrap_flag == 1) {
            av_bprintf(buf, "{\\q1}"); /* End of line wrap */
        } else {
            av_bprintf(buf, "{\\q2}"); /* No wrap */
        }
    }
 
    while (text < text_end) {
        int len;
 
        if ((m->box_flags & STYL_BOX) && entry < m->style_entries) {
            const StyleBox *style = &m->s[entry];
            if (text_pos == style->end) {
                av_bprintf(buf, "{\\r}");
                color = default_style->color;
                entry++;
                style++;
            }
            if (entry < m->style_entries && text_pos == style->start) {
                if (style->bold ^ default_style->bold)
                    av_bprintf(buf, "{\\b%d}", style->bold);
                if (style->italic ^ default_style->italic)
                    av_bprintf(buf, "{\\i%d}", style->italic);
                if (style->underline ^ default_style->underline)
                    av_bprintf(buf, "{\\u%d}", style->underline);
                if (style->fontsize != default_style->fontsize)
                    av_bprintf(buf, "{\\fs%d}", style->fontsize);
                if (style->font_id != default_style->font_id)
                    for (i = 0; i < m->ftab_entries; i++) {
                        if (style->font_id == m->ftab[i].font_id)
                            av_bprintf(buf, "{\\fn%s}", m->ftab[i].font);
                    }
                if (default_style->color != style->color) {
                    color = style->color;
                    av_bprintf(buf, "{\\1c&H%X&}", color);
                }
                if (default_style->alpha != style->alpha)
                    av_bprintf(buf, "{\\1a&H%02X&}", 255 - style->alpha);
            }
        }
        if (m->box_flags & HLIT_BOX) {
            if (text_pos == m->h.hlit_start) {
                /* If hclr box is present, set the secondary color to the color
                 * specified. Otherwise, set primary color to white and secondary
                 * color to black. These colors will come from TextSampleModifier
                 * boxes in future and inverse video technique for highlight will
                 * be implemented.
                 */
                if (m->box_flags & HCLR_BOX) {
                    av_bprintf(buf, "{\\2c&H%02x%02x%02x&}", m->c.hlit_color[2],
                                m->c.hlit_color[1], m->c.hlit_color[0]);
                } else {
                    av_bprintf(buf, "{\\1c&H000000&}{\\2c&HFFFFFF&}");
                }
            }
            if (text_pos == m->h.hlit_end) {
                if (m->box_flags & HCLR_BOX) {
                    av_bprintf(buf, "{\\2c&H%X&}", default_style->color);
                } else {
                    av_bprintf(buf, "{\\1c&H%X&}{\\2c&H%X&}",
                               color, default_style->color);
                }
            }
        }
 
        len = get_utf8_length_at(text, text_end);
        if (len < 1) {
            av_log(avctx, AV_LOG_ERROR, "invalid UTF-8 byte in subtitle\n");
            len = 1;
        }
        switch (*text) {
        case '\r':
            break;
        case '\n':
            av_bprintf(buf, "\\N");
            break;
        default:
            av_bprint_append_data(buf, text, len);
            break;
        }
        text += len;
        text_pos++;
    }
 
    return 0;
}
 
static av_cold int mov_text_init(AVCodecContext *avctx) {
    /*
     * TODO: Handle the default text style.
     * NB: Most players ignore styles completely, with the result that
     * it's very common to find files where the default style is broken
     * and respecting it results in a worse experience than ignoring it.
     */
    int ret;
    MovTextContext *m = avctx->priv_data;
    ret = mov_text_tx3g(avctx, m);
    if (ret == 0) {
        const StyleBox *const default_style = &m->d.style;
        if (!m->frame_width || !m->frame_height) {
            m->frame_width = ASS_DEFAULT_PLAYRESX;
            m->frame_height = ASS_DEFAULT_PLAYRESY;
        }
        return ff_ass_subtitle_header_full(avctx,
                    m->frame_width, m->frame_height,
                    m->d.font, default_style->fontsize,
                    (255U - default_style->alpha) << 24 | default_style->color,
                    (255U - default_style->alpha) << 24 | default_style->color,
                    (255U - m->d.back_alpha) << 24 | m->d.back_color,
                    (255U - m->d.back_alpha) << 24 | m->d.back_color,
                    default_style->bold, default_style->italic, default_style->underline,
                    ASS_DEFAULT_BORDERSTYLE, m->d.alignment);
    } else
        return ff_ass_subtitle_header_default(avctx);
}
 
static int mov_text_decode_frame(AVCodecContext *avctx, AVSubtitle *sub,
                                 int *got_sub_ptr, const AVPacket *avpkt)
{
    MovTextContext *m = avctx->priv_data;
    int ret;
    AVBPrint buf;
    const char *ptr = avpkt->data, *end;
    int text_length;
    size_t i;
 
    if (!ptr || avpkt->size < 2)
        return AVERROR_INVALIDDATA;
 
    /*
     * A packet of size two with value zero is an empty subtitle
     * used to mark the end of the previous non-empty subtitle.
     * We can just drop them here as we have duration information
     * already. If the value is non-zero, then it's technically a
     * bad packet.
     */
    if (avpkt->size == 2)
        return AV_RB16(ptr) == 0 ? 0 : AVERROR_INVALIDDATA;
 
    /*
     * The first two bytes of the packet are the length of the text string
     * In complex cases, there are style descriptors appended to the string
     * so we can't just assume the packet size is the string size.
     */
    text_length = AV_RB16(ptr);
    end = ptr + FFMIN(2 + text_length, avpkt->size);
    ptr += 2;
 
    mov_text_cleanup(m);
 
    m->style_entries = 0;
    m->box_flags = 0;
    // Note that the spec recommends lines be no longer than 2048 characters.
    av_bprint_init(&buf, 0, AV_BPRINT_SIZE_UNLIMITED);
    if (text_length + 2 < avpkt->size) {
        const uint8_t *tsmb = end;
        const uint8_t *const tsmb_end = avpkt->data + avpkt->size;
        // A box is a minimum of 8 bytes.
        while (tsmb_end - tsmb >= 8) {
            uint64_t tsmb_size = bytestream_get_be32(&tsmb);
            uint32_t tsmb_type = bytestream_get_be32(&tsmb);
            int size_var, ret_tsmb;
 
            if (tsmb_size == 1) {
                if (tsmb_end - tsmb < 8)
                    break;
                tsmb_size = bytestream_get_be64(&tsmb);
                size_var = 16;
            } else
                size_var = 8;
            //size_var is equal to 8 or 16 depending on the size of box
 
            if (tsmb_size < size_var) {
                av_log(avctx, AV_LOG_ERROR, "tsmb_size invalid\n");
                return AVERROR_INVALIDDATA;
            }
            tsmb_size -= size_var;
 
            if (tsmb_end - tsmb < tsmb_size)
                break;
 
            for (i = 0; i < box_count; i++) {
                if (tsmb_type == box_types[i].type) {
                    if (tsmb_size < box_types[i].base_size)
                        break;
                    ret_tsmb = box_types[i].decode(tsmb, m, tsmb_size);
                    if (ret_tsmb == -1)
                        break;
                }
            }
            tsmb += tsmb_size;
        }
        text_to_ass(&buf, ptr, end, avctx);
        mov_text_cleanup(m);
    } else
        text_to_ass(&buf, ptr, end, avctx);
 
    ret = ff_ass_add_rect(sub, buf.str, m->readorder++, 0, NULL, NULL);
    av_bprint_finalize(&buf, NULL);
    if (ret < 0)
        return ret;
    *got_sub_ptr = sub->num_rects > 0;
    return avpkt->size;
}
 
static av_cold int mov_text_decode_close(AVCodecContext *avctx)
{
    MovTextContext *m = avctx->priv_data;
    mov_text_cleanup_ftab(m);
    mov_text_cleanup(m);
    return 0;
}
 
static av_cold void mov_text_flush(AVCodecContext *avctx)
{
    MovTextContext *m = avctx->priv_data;
    if (!(avctx->flags2 & AV_CODEC_FLAG2_RO_FLUSH_NOOP))
        m->readorder = 0;
}
 
#define OFFSET(x) offsetof(MovTextContext, x)
#define FLAGS AV_OPT_FLAG_DECODING_PARAM | AV_OPT_FLAG_SUBTITLE_PARAM
static const AVOption options[] = {
    { "width", "Frame width, usually video width", OFFSET(frame_width), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX, FLAGS },
    { "height", "Frame height, usually video height", OFFSET(frame_height), AV_OPT_TYPE_INT, {.i64=0}, 0, INT_MAX, FLAGS },
    { NULL },
};
 
static const AVClass mov_text_decoder_class = {
    .class_name = "MOV text decoder",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};
 
const FFCodec ff_movtext_decoder = {
    .p.name       = "mov_text",
    CODEC_LONG_NAME("3GPP Timed Text subtitle"),
    .p.type       = AVMEDIA_TYPE_SUBTITLE,
    .p.id         = AV_CODEC_ID_MOV_TEXT,
    .priv_data_size = sizeof(MovTextContext),
    .p.priv_class = &mov_text_decoder_class,
    .init         = mov_text_init,
    FF_CODEC_DECODE_SUB_CB(mov_text_decode_frame),
    .close        = mov_text_decode_close,
    .flush        = mov_text_flush,
};