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ffmpeg/libavcodec/movtextdec.c
Andreas Rheinhardt cc1251ab81 avcodec/movtextdec: Sanitize style entries 
There are three types of style entries which are redundant:
a) Entries with length zero. They are already discarded.
b) Entries that are equivalent to the default style:
They can be safely discarded.
c) Entries that are equivalent to the immediately preceding style
if the start of the current style coincides with the end of the
preceding style. In this case the styles can be merged.

This commit implements discarding/merging in cases b) and c).
This fixes ticket #9548. In said ticket each packet contained
exactly one style entry that covered the complete packet with
the exception of the last character (probably created by a tool
that didn't know that the style's end is exclusive). Said style
coincided with the default style, leading to a superfluous reset,
which is now gone.

Reviewed-by: Philip Langdale <philipl@overt.org>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
2021-12-08 21:00:52 +01:00

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/*
* 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 "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;
uint64_t tracksize;
int size_var;
int readorder;
int frame_width;
int frame_height;
} MovTextContext;
typedef struct {
uint32_t type;
size_t base_size;
int (*decode)(const uint8_t *tsmb, MovTextContext *m, const AVPacket *avpkt);
} 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, const AVPacket *avpkt)
{
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, const AVPacket *avpkt)
{
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, const AVPacket *avpkt)
{
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, const AVPacket *avpkt)
{
int i;
int style_entries = bytestream_get_be16(&tsmb);
StyleBox *tmp;
// A single style record is of length 12 bytes.
if (m->tracksize + m->size_var + 2 + style_entries * 12 > avpkt->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(ENOMEM);
}
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 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,
void *data, int *got_sub_ptr, AVPacket *avpkt)
{
AVSubtitle *sub = data;
MovTextContext *m = avctx->priv_data;
int ret;
AVBPrint buf;
char *ptr = avpkt->data;
char *end;
int text_length, tsmb_type, ret_tsmb;
uint64_t tsmb_size;
const uint8_t *tsmb;
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);
tsmb_size = 0;
m->tracksize = 2 + text_length;
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) {
while (m->tracksize + 8 <= avpkt->size) {
// A box is a minimum of 8 bytes.
tsmb = ptr + m->tracksize - 2;
tsmb_size = AV_RB32(tsmb);
tsmb += 4;
tsmb_type = AV_RB32(tsmb);
tsmb += 4;
if (tsmb_size == 1) {
if (m->tracksize + 16 > avpkt->size)
break;
tsmb_size = AV_RB64(tsmb);
tsmb += 8;
m->size_var = 16;
} else
m->size_var = 8;
//size_var is equal to 8 or 16 depending on the size of box
if (tsmb_size == 0) {
av_log(avctx, AV_LOG_ERROR, "tsmb_size is 0\n");
return AVERROR_INVALIDDATA;
}
if (tsmb_size > avpkt->size - m->tracksize)
break;
for (i = 0; i < box_count; i++) {
if (tsmb_type == box_types[i].type) {
if (m->tracksize + m->size_var + box_types[i].base_size > avpkt->size)
break;
ret_tsmb = box_types[i].decode(tsmb, m, avpkt);
if (ret_tsmb == -1)
break;
}
}
m->tracksize = m->tracksize + 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 int mov_text_decode_close(AVCodecContext *avctx)
{
MovTextContext *m = avctx->priv_data;
mov_text_cleanup_ftab(m);
mov_text_cleanup(m);
return 0;
}
static 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 AVCodec ff_movtext_decoder = {
.name = "mov_text",
.long_name = NULL_IF_CONFIG_SMALL("3GPP Timed Text subtitle"),
.type = AVMEDIA_TYPE_SUBTITLE,
.id = AV_CODEC_ID_MOV_TEXT,
.priv_data_size = sizeof(MovTextContext),
.priv_class = &mov_text_decoder_class,
.init = mov_text_init,
.decode = mov_text_decode_frame,
.close = mov_text_decode_close,
.flush = mov_text_flush,
.caps_internal = FF_CODEC_CAP_INIT_THREADSAFE,
};
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