aboutsummaryrefslogtreecommitdiffstats
path: root/libavformat/rcwtenc.c
blob: 270154b70158d59fe28fa7c2f98de49acd6760b1 (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
/*
 * RCWT (Raw Captions With Time) muxer
 *
 * 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
 */

/*
 * RCWT (Raw Captions With Time) is a format native to ccextractor, a commonly
 * used open source tool for processing 608/708 Closed Captions (CC) sources.
 *
 * This muxer implements the specification as of March 2024, which has
 * been stable and unchanged since April 2014.
 *
 * This muxer will have some nuances from the way that ccextractor muxes RCWT.
 * No compatibility issues when processing the output with ccextractor
 * have been observed as a result of this so far, but mileage may vary
 * and outputs will not be a bit-exact match.
 *
 * Specifically, the differences are:
 * (1) This muxer will identify as "FF" as the writing program identifier, so
 *     as to be honest about the output's origin.
 *
 * (2) This muxer will not alter the extracted data except to remove invalid
 *     packets in between valid CC blocks. On the other hand, ccextractor
 *     will by default remove mid-stream padding, and add padding at the end
 *     of the stream (in order to convey the end time of the source video).
 *
 * A free specification of RCWT can be found here:
 * @url{https://github.com/CCExtractor/ccextractor/blob/master/docs/BINARY_FILE_FORMAT.TXT}
 */

#include "avformat.h"
#include "internal.h"
#include "mux.h"
#include "libavutil/log.h"
#include "libavutil/intreadwrite.h"

#define RCWT_CLUSTER_MAX_BLOCKS             65535
#define RCWT_BLOCK_SIZE                     3

typedef struct RCWTContext {
    int cluster_pos;
    int64_t cluster_pts;
    uint8_t cluster_buf[RCWT_CLUSTER_MAX_BLOCKS * RCWT_BLOCK_SIZE];
} RCWTContext;

static void rcwt_init_cluster(RCWTContext *rcwt)
{
    rcwt->cluster_pos = 0;
    rcwt->cluster_pts = AV_NOPTS_VALUE;
}

static void rcwt_flush_cluster(AVFormatContext *avf)
{
    RCWTContext *rcwt = avf->priv_data;

    if (rcwt->cluster_pos > 0) {
        avio_wl64(avf->pb, rcwt->cluster_pts);
        avio_wl16(avf->pb, rcwt->cluster_pos / RCWT_BLOCK_SIZE);
        avio_write(avf->pb, rcwt->cluster_buf, rcwt->cluster_pos);
    }

    rcwt_init_cluster(rcwt);
}

static int rcwt_write_header(AVFormatContext *avf)
{
    avpriv_set_pts_info(avf->streams[0], 64, 1, 1000);

    /* magic number */
    avio_wb16(avf->pb, 0xCCCC);
    avio_w8(avf->pb, 0xED);

    /* program version (identify as ffmpeg) */
    avio_wb16(avf->pb, 0xFF00);
    avio_w8(avf->pb, 0x60);

    /* format version, only version 0.001 supported for now */
    avio_wb16(avf->pb, 0x0001);

    /* reserved */
    avio_wb16(avf->pb, 0x000);
    avio_w8(avf->pb, 0x00);

    rcwt_init_cluster(avf->priv_data);

    return 0;
}

static int rcwt_write_packet(AVFormatContext *avf, AVPacket *pkt)
{
    RCWTContext *rcwt = avf->priv_data;

    if (pkt->size < RCWT_BLOCK_SIZE)
        return 0;

    /* new PTS, new cluster */
    if (pkt->pts != rcwt->cluster_pts) {
        rcwt_flush_cluster(avf);
        rcwt->cluster_pts = pkt->pts;
    }

    if (pkt->pts == AV_NOPTS_VALUE) {
        av_log(avf, AV_LOG_WARNING, "Ignoring CC packet with no PTS\n");
        return 0;
    }

    for (int i = 0; i <= pkt->size - RCWT_BLOCK_SIZE;) {
        uint8_t cc_valid;
        uint8_t cc_type;

        if (rcwt->cluster_pos == RCWT_CLUSTER_MAX_BLOCKS * RCWT_BLOCK_SIZE) {
            av_log(avf, AV_LOG_WARNING, "Starting new cluster due to size\n");
            rcwt_flush_cluster(avf);
        }

        cc_valid = (pkt->data[i] & 0x04) >> 2;
        cc_type = pkt->data[i] & 0x03;

        if (!(cc_valid || cc_type == 3)) {
            i++;
            continue;
        }

        memcpy(&rcwt->cluster_buf[rcwt->cluster_pos], &pkt->data[i], 3);
        rcwt->cluster_pos += 3;
        i                 += 3;
    }

    return 0;
}

static int rcwt_write_trailer(AVFormatContext *avf)
{
    rcwt_flush_cluster(avf);

    return 0;
}

const FFOutputFormat ff_rcwt_muxer = {
    .p.name             = "rcwt",
    .p.long_name        = NULL_IF_CONFIG_SMALL("RCWT (Raw Captions With Time)"),
    .p.flags            = AVFMT_GLOBALHEADER | AVFMT_VARIABLE_FPS | AVFMT_TS_NONSTRICT,
    .p.video_codec      = AV_CODEC_ID_NONE,
    .p.audio_codec      = AV_CODEC_ID_NONE,
    .p.subtitle_codec   = AV_CODEC_ID_EIA_608,
    .flags_internal     = FF_OFMT_FLAG_MAX_ONE_OF_EACH |
                          FF_OFMT_FLAG_ONLY_DEFAULT_CODECS,
    .priv_data_size     = sizeof(RCWTContext),
    .write_header       = rcwt_write_header,
    .write_packet       = rcwt_write_packet,
    .write_trailer      = rcwt_write_trailer
};