aboutsummaryrefslogtreecommitdiffstats
path: root/libavcodec/movtextenc.c
blob: 7aa74d7c9d05faa37be1b47645dda0ccf908fb74 (plain) (blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
/*
 * 3GPP TS 26.245 Timed Text encoder
 * 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 <stdarg.h>
#include "avcodec.h"
#include "libavutil/opt.h"
#include "libavutil/avstring.h"
#include "libavutil/intreadwrite.h"
#include "libavutil/mem.h"
#include "libavutil/common.h"
#include "ass_split.h"
#include "ass.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 STYLE_RECORD_SIZE       12
#define SIZE_ADD                10

#define STYL_BOX   (1<<0)
#define HLIT_BOX   (1<<1)
#define HCLR_BOX   (1<<2)

#define DEFAULT_STYLE_FONT_ID  0x01
#define DEFAULT_STYLE_FONTSIZE 0x12
#define DEFAULT_STYLE_COLOR    0xffffffff
#define DEFAULT_STYLE_FLAG     0x00

#define BGR_TO_RGB(c) (((c) & 0xff) << 16 | ((c) & 0xff00) | (((uint32_t)(c) >> 16) & 0xff))
#define FONTSIZE_SCALE(s,fs) ((fs) * (s)->font_scale_factor + 0.5)
#define av_bprint_append_any(buf, data, size)   av_bprint_append_data(buf, ((const char*)data), size)

typedef struct {
    uint16_t style_start;
    uint16_t style_end;
    uint8_t style_flag;
    uint16_t style_fontID;
    uint8_t style_fontsize;
    uint32_t style_color;
} StyleBox;

typedef struct {
    uint16_t start;
    uint16_t end;
} HighlightBox;

typedef struct {
   uint32_t color;
} HilightcolorBox;

typedef struct {
    AVClass *class;
    AVCodecContext *avctx;

    ASSSplitContext *ass_ctx;
    ASSStyle *ass_dialog_style;
    StyleBox *style_attributes;
    unsigned  count;
    unsigned  style_attributes_bytes_allocated;
    StyleBox  style_attributes_temp;
    AVBPrint buffer;
    HighlightBox hlit;
    HilightcolorBox hclr;
    uint8_t box_flags;
    StyleBox d;
    uint16_t text_pos;
    char **fonts;
    int font_count;
    double font_scale_factor;
    int frame_height;
} MovTextContext;

typedef struct {
    void (*encode)(MovTextContext *s);
} Box;

static void mov_text_cleanup(MovTextContext *s)
{
    s->count = 0;
    s->style_attributes_temp = s->d;
}

static void encode_styl(MovTextContext *s)
{
    if ((s->box_flags & STYL_BOX) && s->count) {
        uint8_t buf[12], *p = buf;

        bytestream_put_be32(&p, s->count * STYLE_RECORD_SIZE + SIZE_ADD);
        bytestream_put_be32(&p, MKBETAG('s','t','y','l'));
        bytestream_put_be16(&p, s->count);
        /*The above three attributes are hard coded for now
        but will come from ASS style in the future*/
        av_bprint_append_any(&s->buffer, buf, 10);
        for (unsigned j = 0; j < s->count; j++) {
            const StyleBox *style = &s->style_attributes[j];

            p = buf;
            bytestream_put_be16(&p, style->style_start);
            bytestream_put_be16(&p, style->style_end);
            bytestream_put_be16(&p, style->style_fontID);
            bytestream_put_byte(&p, style->style_flag);
            bytestream_put_byte(&p, style->style_fontsize);
            bytestream_put_be32(&p, style->style_color);

            av_bprint_append_any(&s->buffer, buf, 12);
        }
    }
    mov_text_cleanup(s);
}

static void encode_hlit(MovTextContext *s)
{
    if (s->box_flags & HLIT_BOX) {
        uint8_t buf[12], *p = buf;

        bytestream_put_be32(&p, 12);
        bytestream_put_be32(&p, MKBETAG('h','l','i','t'));
        bytestream_put_be16(&p, s->hlit.start);
        bytestream_put_be16(&p, s->hlit.end);

        av_bprint_append_any(&s->buffer, buf, 12);
    }
}

static void encode_hclr(MovTextContext *s)
{
    if (s->box_flags & HCLR_BOX) {
        uint8_t buf[12], *p = buf;

        bytestream_put_be32(&p, 12);
        bytestream_put_be32(&p, MKBETAG('h','c','l','r'));
        bytestream_put_be32(&p, s->hclr.color);

        av_bprint_append_any(&s->buffer, buf, 12);
    }
}

static const Box box_types[] = {
    { encode_styl },
    { encode_hlit },
    { encode_hclr },
};

const static size_t box_count = FF_ARRAY_ELEMS(box_types);

static int mov_text_encode_close(AVCodecContext *avctx)
{
    MovTextContext *s = avctx->priv_data;

    ff_ass_split_free(s->ass_ctx);
    av_freep(&s->style_attributes);
    av_freep(&s->fonts);
    av_bprint_finalize(&s->buffer, NULL);
    return 0;
}

static int encode_sample_description(AVCodecContext *avctx)
{
    ASS *ass;
    ASSStyle *style;
    int i, j;
    uint32_t back_color = 0;
    int font_names_total_len = 0;
    MovTextContext *s = avctx->priv_data;
    uint8_t buf[30], *p = buf;

    //  0x00, 0x00, 0x00, 0x00, // uint32_t displayFlags
    //  0x01,                   // int8_t horizontal-justification
    //  0xFF,                   // int8_t vertical-justification
    //  0x00, 0x00, 0x00, 0x00, // uint8_t background-color-rgba[4]
    //     BoxRecord {
    //  0x00, 0x00,             // int16_t top
    //  0x00, 0x00,             // int16_t left
    //  0x00, 0x00,             // int16_t bottom
    //  0x00, 0x00,             // int16_t right
    //     };
    //     StyleRecord {
    //  0x00, 0x00,             // uint16_t startChar
    //  0x00, 0x00,             // uint16_t endChar
    //  0x00, 0x01,             // uint16_t font-ID
    //  0x00,                   // uint8_t face-style-flags
    //  0x12,                   // uint8_t font-size
    //  0xFF, 0xFF, 0xFF, 0xFF, // uint8_t text-color-rgba[4]
    //     };
    //     FontTableBox {
    //  0x00, 0x00, 0x00, 0x12, // uint32_t size
    //  'f', 't', 'a', 'b',     // uint8_t name[4]
    //  0x00, 0x01,             // uint16_t entry-count
    //     FontRecord {
    //  0x00, 0x01,             // uint16_t font-ID
    //  0x05,                   // uint8_t font-name-length
    //  'S', 'e', 'r', 'i', 'f',// uint8_t font[font-name-length]
    //     };
    //     };

    // Populate sample description from ASS header
    ass = (ASS*)s->ass_ctx;
    // Compute font scaling factor based on (optionally) provided
    // output video height and ASS script play_res_y
    if (s->frame_height && ass->script_info.play_res_y)
        s->font_scale_factor = (double)s->frame_height / ass->script_info.play_res_y;
    else
        s->font_scale_factor = 1;

    style = ff_ass_style_get(s->ass_ctx, "Default");
    if (!style && ass->styles_count) {
        style = &ass->styles[0];
    }
    s->d.style_fontID   = DEFAULT_STYLE_FONT_ID;
    s->d.style_fontsize = DEFAULT_STYLE_FONTSIZE;
    s->d.style_color    = DEFAULT_STYLE_COLOR;
    s->d.style_flag     = DEFAULT_STYLE_FLAG;
    if (style) {
        s->d.style_fontsize = FONTSIZE_SCALE(s, style->font_size);
        s->d.style_color = BGR_TO_RGB(style->primary_color & 0xffffff) << 8 |
                           255 - ((uint32_t)style->primary_color >> 24);
        s->d.style_flag = (!!style->bold      * STYLE_FLAG_BOLD)   |
                          (!!style->italic    * STYLE_FLAG_ITALIC) |
                          (!!style->underline * STYLE_FLAG_UNDERLINE);
        back_color = (BGR_TO_RGB(style->back_color & 0xffffff) << 8) |
                     (255 - ((uint32_t)style->back_color >> 24));
    }

    bytestream_put_be32(&p, 0); // displayFlags
    bytestream_put_be16(&p, 0x01FF); // horizontal/vertical justification (2x int8_t)
    bytestream_put_be32(&p, back_color);
    bytestream_put_be64(&p, 0); // BoxRecord - 4xint16_t: top, left, bottom, right
    //     StyleRecord {
    bytestream_put_be16(&p, s->d.style_start);
    bytestream_put_be16(&p, s->d.style_end);
    bytestream_put_be16(&p, s->d.style_fontID);
    bytestream_put_byte(&p, s->d.style_flag);
    bytestream_put_byte(&p, s->d.style_fontsize);
    bytestream_put_be32(&p, s->d.style_color);
    //     };
    av_bprint_append_any(&s->buffer, buf, 30);

    // Build font table
    // We can't build a complete font table since that would require
    // scanning all dialogs first.  But we can at least fill in what
    // is avaiable in the ASS header
    if (style && ass->styles_count) {
        // Find unique font names
        if (style->font_name) {
            av_dynarray_add(&s->fonts, &s->font_count, style->font_name);
            font_names_total_len += strlen(style->font_name);
        }
        for (i = 0; i < ass->styles_count; i++) {
            int found = 0;
            if (!ass->styles[i].font_name)
                continue;
            for (j = 0; j < s->font_count; j++) {
                if (!strcmp(s->fonts[j], ass->styles[i].font_name)) {
                    found = 1;
                    break;
                }
            }
            if (!found) {
                av_dynarray_add(&s->fonts, &s->font_count,
                                           ass->styles[i].font_name);
                font_names_total_len += strlen(ass->styles[i].font_name);
            }
        }
    } else
        av_dynarray_add(&s->fonts, &s->font_count, (char*)"Serif");

    //     FontTableBox {
    p = buf;
    bytestream_put_be32(&p, SIZE_ADD + 3 * s->font_count + font_names_total_len); // Size
    bytestream_put_be32(&p, MKBETAG('f','t','a','b'));
    bytestream_put_be16(&p, s->font_count);

    av_bprint_append_any(&s->buffer, buf, 10);
    //     FontRecord {
    for (i = 0; i < s->font_count; i++) {
        size_t len = strlen(s->fonts[i]);

        p = buf;
        bytestream_put_be16(&p, i + 1); //fontID
        bytestream_put_byte(&p, len);

        av_bprint_append_any(&s->buffer, buf, 3);
        av_bprint_append_any(&s->buffer, s->fonts[i], len);
    }
    //     };
    //     };

    if (!av_bprint_is_complete(&s->buffer)) {
        return AVERROR(ENOMEM);
    }

    avctx->extradata_size = s->buffer.len;
    avctx->extradata = av_mallocz(avctx->extradata_size + AV_INPUT_BUFFER_PADDING_SIZE);
    if (!avctx->extradata) {
        return AVERROR(ENOMEM);
    }

    memcpy(avctx->extradata, s->buffer.str, avctx->extradata_size);
    av_bprint_clear(&s->buffer);

    return 0;
}

static av_cold int mov_text_encode_init(AVCodecContext *avctx)
{
    int ret;
    MovTextContext *s = avctx->priv_data;
    s->avctx = avctx;

    av_bprint_init(&s->buffer, 0, AV_BPRINT_SIZE_UNLIMITED);

    s->ass_ctx = ff_ass_split(avctx->subtitle_header);
    if (!s->ass_ctx)
        return AVERROR_INVALIDDATA;
    ret = encode_sample_description(avctx);
    if (ret < 0)
        return ret;

    return 0;
}

// Start a new style box if needed
static int mov_text_style_start(MovTextContext *s)
{
    // there's an existing style entry
    if (s->style_attributes_temp.style_start == s->text_pos)
        // Still at same text pos, use same entry
        return 1;
    if (s->style_attributes_temp.style_flag     != s->d.style_flag   ||
        s->style_attributes_temp.style_color    != s->d.style_color  ||
        s->style_attributes_temp.style_fontID   != s->d.style_fontID ||
        s->style_attributes_temp.style_fontsize != s->d.style_fontsize) {
        StyleBox *tmp;

        // last style != defaults, end the style entry and start a new one
        if (s->count + 1 > FFMIN(SIZE_MAX / sizeof(*s->style_attributes), UINT16_MAX) ||
            !(tmp = av_fast_realloc(s->style_attributes,
                                    &s->style_attributes_bytes_allocated,
                                    (s->count + 1) * sizeof(*s->style_attributes)))) {
            mov_text_cleanup(s);
            av_bprint_clear(&s->buffer);
            s->box_flags &= ~STYL_BOX;
            return 0;
        }
        s->style_attributes = tmp;
        s->style_attributes_temp.style_end = s->text_pos;
        s->style_attributes[s->count++] = s->style_attributes_temp;
        s->box_flags |= STYL_BOX;
        s->style_attributes_temp = s->d;
        s->style_attributes_temp.style_start = s->text_pos;
    } else { // style entry matches defaults, drop entry
        s->style_attributes_temp = s->d;
        s->style_attributes_temp.style_start = s->text_pos;
    }
    return 1;
}

static uint8_t mov_text_style_to_flag(const char style)
{
    uint8_t style_flag = 0;

    switch (style){
    case 'b':
        style_flag = STYLE_FLAG_BOLD;
        break;
    case 'i':
        style_flag = STYLE_FLAG_ITALIC;
        break;
    case 'u':
        style_flag = STYLE_FLAG_UNDERLINE;
        break;
    }
    return style_flag;
}

static void mov_text_style_set(MovTextContext *s, uint8_t style_flags)
{
    if (!((s->style_attributes_temp.style_flag & style_flags) ^ style_flags)) {
        // setting flags that that are already set
        return;
    }
    if (mov_text_style_start(s))
        s->style_attributes_temp.style_flag |= style_flags;
}

static void mov_text_style_cb(void *priv, const char style, int close)
{
    MovTextContext *s = priv;
    uint8_t style_flag = mov_text_style_to_flag(style);

    if (!!(s->style_attributes_temp.style_flag & style_flag) != close) {
        // setting flag that is already set
        return;
    }
    if (mov_text_style_start(s)) {
        if (!close)
            s->style_attributes_temp.style_flag |= style_flag;
        else
            s->style_attributes_temp.style_flag &= ~style_flag;
    }
}

static void mov_text_color_set(MovTextContext *s, uint32_t color)
{
    if ((s->style_attributes_temp.style_color & 0xffffff00) == color) {
        // color hasn't changed
        return;
    }
    if (mov_text_style_start(s))
        s->style_attributes_temp.style_color = (color & 0xffffff00) |
                            (s->style_attributes_temp.style_color & 0xff);
}

static void mov_text_color_cb(void *priv, unsigned int color, unsigned int color_id)
{
    MovTextContext *s = priv;

    color = BGR_TO_RGB(color) << 8;
    if (color_id == 1) {    //primary color changes
        mov_text_color_set(s, color);
    } else if (color_id == 2) {    //secondary color changes
        if (!(s->box_flags & HCLR_BOX))
            // Highlight alpha not set yet, use current primary alpha
            s->hclr.color = s->style_attributes_temp.style_color;
        if (!(s->box_flags & HLIT_BOX) || s->hlit.start == s->text_pos) {
            s->box_flags |= HCLR_BOX;
            s->box_flags |= HLIT_BOX;
            s->hlit.start = s->text_pos;
            s->hclr.color = color | (s->hclr.color & 0xFF);
        }
        else //close tag
            s->hlit.end = s->text_pos;
        /* If there are more than one secondary color changes in ASS,
           take start of first section and end of last section. Movtext
           allows only one highlight box per sample.
         */
    }
    // Movtext does not support changes to other color_id (outline, background)
}

static void mov_text_alpha_set(MovTextContext *s, uint8_t alpha)
{
    if ((s->style_attributes_temp.style_color & 0xff) == alpha) {
        // color hasn't changed
        return;
    }
    if (mov_text_style_start(s))
        s->style_attributes_temp.style_color =
                (s->style_attributes_temp.style_color & 0xffffff00) | alpha;
}

static void mov_text_alpha_cb(void *priv, int alpha, int alpha_id)
{
    MovTextContext *s = priv;

    alpha = 255 - alpha;
    if (alpha_id == 1) // primary alpha changes
        mov_text_alpha_set(s, alpha);
    else if (alpha_id == 2) {    //secondary alpha changes
        if (!(s->box_flags & HCLR_BOX))
            // Highlight color not set yet, use current primary color
            s->hclr.color = s->style_attributes_temp.style_color;
        if (!(s->box_flags & HLIT_BOX) || s->hlit.start == s->text_pos) {
            s->box_flags |= HCLR_BOX;
            s->box_flags |= HLIT_BOX;
            s->hlit.start = s->text_pos;
            s->hclr.color = (s->hclr.color & 0xffffff00) | alpha;
        }
        else //close tag
            s->hlit.end = s->text_pos;
    }
    // Movtext does not support changes to other alpha_id (outline, background)
}

static uint16_t find_font_id(MovTextContext *s, const char *name)
{
    if (!name)
        return 1;

    for (int i = 0; i < s->font_count; i++) {
        if (!strcmp(name, s->fonts[i]))
            return i + 1;
    }
    return 1;
}

static void mov_text_font_name_set(MovTextContext *s, const char *name)
{
    int fontID = find_font_id(s, name);
    if (s->style_attributes_temp.style_fontID == fontID) {
        // color hasn't changed
        return;
    }
    if (mov_text_style_start(s))
        s->style_attributes_temp.style_fontID = fontID;
}

static void mov_text_font_name_cb(void *priv, const char *name)
{
    mov_text_font_name_set((MovTextContext*)priv, name);
}

static void mov_text_font_size_set(MovTextContext *s, int size)
{
    size = FONTSIZE_SCALE(s, size);
    if (s->style_attributes_temp.style_fontsize == size) {
        // color hasn't changed
        return;
    }
    if (mov_text_style_start(s))
        s->style_attributes_temp.style_fontsize = size;
}

static void mov_text_font_size_cb(void *priv, int size)
{
    mov_text_font_size_set((MovTextContext*)priv, size);
}

static void mov_text_end_cb(void *priv)
{
    // End of text, close any open style record
    mov_text_style_start((MovTextContext*)priv);
}

static void mov_text_ass_style_set(MovTextContext *s, ASSStyle *style)
{
    uint8_t    style_flags, alpha;
    uint32_t   color;

    if (style) {
        style_flags = (!!style->bold      * STYLE_FLAG_BOLD)   |
                      (!!style->italic    * STYLE_FLAG_ITALIC) |
                      (!!style->underline * STYLE_FLAG_UNDERLINE);
        mov_text_style_set(s, style_flags);
        color = BGR_TO_RGB(style->primary_color & 0xffffff) << 8;
        mov_text_color_set(s, color);
        alpha = 255 - ((uint32_t)style->primary_color >> 24);
        mov_text_alpha_set(s, alpha);
        mov_text_font_size_set(s, style->font_size);
        mov_text_font_name_set(s, style->font_name);
    } else {
        // End current style record, go back to defaults
        mov_text_style_start(s);
    }
}

static void mov_text_dialog(MovTextContext *s, ASSDialog *dialog)
{
    ASSStyle *style = ff_ass_style_get(s->ass_ctx, dialog->style);

    s->ass_dialog_style = style;
    mov_text_ass_style_set(s, style);
}

static void mov_text_cancel_overrides_cb(void *priv, const char *style_name)
{
    MovTextContext *s = priv;
    ASSStyle *style;

    if (!style_name || !*style_name)
        style = s->ass_dialog_style;
    else
        style= ff_ass_style_get(s->ass_ctx, style_name);

    mov_text_ass_style_set(s, style);
}

static unsigned utf8_strlen(const char *text, int len)
{
    unsigned i = 0, ret = 0;
    while (i < len) {
        char c = text[i];
        if ((c & 0x80) == 0)
            i += 1;
        else if ((c & 0xE0) == 0xC0)
            i += 2;
        else if ((c & 0xF0) == 0xE0)
            i += 3;
        else if ((c & 0xF8) == 0xF0)
            i += 4;
        else
            return 0;
        ret++;
    }
    return ret;
}

static void mov_text_text_cb(void *priv, const char *text, int len)
{
    unsigned utf8_len = utf8_strlen(text, len);
    MovTextContext *s = priv;
    av_bprint_append_data(&s->buffer, text, len);
    // If it's not utf-8, just use the byte length
    s->text_pos += utf8_len ? utf8_len : len;
}

static void mov_text_new_line_cb(void *priv, int forced)
{
    MovTextContext *s = priv;
    s->text_pos += 1;
    av_bprint_chars(&s->buffer, '\n', 1);
}

static const ASSCodesCallbacks mov_text_callbacks = {
    .text             = mov_text_text_cb,
    .new_line         = mov_text_new_line_cb,
    .style            = mov_text_style_cb,
    .color            = mov_text_color_cb,
    .alpha            = mov_text_alpha_cb,
    .font_name        = mov_text_font_name_cb,
    .font_size        = mov_text_font_size_cb,
    .cancel_overrides = mov_text_cancel_overrides_cb,
    .end              = mov_text_end_cb,
};

static int mov_text_encode_frame(AVCodecContext *avctx, unsigned char *buf,
                                 int bufsize, const AVSubtitle *sub)
{
    MovTextContext *s = avctx->priv_data;
    ASSDialog *dialog;
    int i, length;

    s->text_pos = 0;
    s->count = 0;
    s->box_flags = 0;
    av_bprint_clear(&s->buffer);
    for (i = 0; i < sub->num_rects; i++) {
        const char *ass = sub->rects[i]->ass;

        if (sub->rects[i]->type != SUBTITLE_ASS) {
            av_log(avctx, AV_LOG_ERROR, "Only SUBTITLE_ASS type supported.\n");
            return AVERROR(EINVAL);
        }

        dialog = ff_ass_split_dialog(s->ass_ctx, ass);
        if (!dialog)
            return AVERROR(ENOMEM);
        mov_text_dialog(s, dialog);
        ff_ass_split_override_codes(&mov_text_callbacks, s, dialog->text);
        ff_ass_free_dialog(&dialog);
    }

    if (s->buffer.len > UINT16_MAX)
        return AVERROR(ERANGE);
    AV_WB16(buf, s->buffer.len);
    buf += 2;

    for (size_t j = 0; j < box_count; j++)
        box_types[j].encode(s);

    if (!av_bprint_is_complete(&s->buffer))
        return AVERROR(ENOMEM);

    if (!s->buffer.len)
        return 0;

    if (s->buffer.len > bufsize - 3) {
        av_log(avctx, AV_LOG_ERROR, "Buffer too small for ASS event.\n");
        return AVERROR_BUFFER_TOO_SMALL;
    }

    memcpy(buf, s->buffer.str, s->buffer.len);
    length = s->buffer.len + 2;

    return length;
}

#define OFFSET(x) offsetof(MovTextContext, x)
#define FLAGS AV_OPT_FLAG_ENCODING_PARAM | AV_OPT_FLAG_SUBTITLE_PARAM
static const AVOption options[] = {
    { "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_encoder_class = {
    .class_name = "MOV text enoder",
    .item_name  = av_default_item_name,
    .option     = options,
    .version    = LIBAVUTIL_VERSION_INT,
};

const FFCodec ff_movtext_encoder = {
    .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_encoder_class,
    .init           = mov_text_encode_init,
    FF_CODEC_ENCODE_SUB_CB(mov_text_encode_frame),
    .close          = mov_text_encode_close,
    .caps_internal  = FF_CODEC_CAP_INIT_CLEANUP,
};