movtextenc: 3GPP TS 26.245 Timed Text Encoder.

This change introduces a basic encoder for 3GPP Timed Text subtitles,
also known as TX3G, Quicktime subtitles, or "movtext" in the existing
code.

This initial change doesn't attempt to write styling information,
and just writes the plain text of the subtitles. I intend to add
support for styles eventually, but it's challenging due to a lack
of existing players that support them.

Note that an additional change is required to the mov/mp4 muxer to
write empty subtitle packets to indicate subtitle duration.

Signed-off-by: Philip Langdale <philipl@overt.org>

1 files changed, 162 insertions, 0 deletions

diff --git a/libavcodec/movtextenc.c b/libavcodec/movtextenc.c
new file mode 100644
index 0000000..027efd5
--- /dev/null
+++ b/libavcodec/movtextenc.c
@@ -0,0 +1,162 @@
+/*
+ * 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 "movtext.h"
+#include "libavutil/avstring.h"
+#include "ass_split.h"
+#include "ass.h"
+
+typedef struct {
+    ASSSplitContext *ass_ctx;
+    char buffer[2048];
+    char *ptr;
+    char *end;
+} MovTextContext;
+
+
+static av_cold int mov_text_encode_init(AVCodecContext *avctx)
+{
+    /*
+     * For now, we'll use a fixed default style. When we add styling
+     * support, this will be generated from the ASS style.
+     */
+    static uint8_t text_sample_entry[] = {
+        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]
+        // };
+        // };
+    };
+
+    MovTextContext *s = avctx->priv_data;
+
+    avctx->extradata_size = sizeof text_sample_entry;
+    avctx->extradata = av_mallocz(avctx->extradata_size);
+    if (!avctx->extradata)
+        return AVERROR(ENOMEM);
+
+    memcpy(avctx->extradata, text_sample_entry, avctx->extradata_size);
+
+    s->ass_ctx = ff_ass_split(avctx->subtitle_header);
+    return s->ass_ctx ? 0 : AVERROR_INVALIDDATA;
+}
+
+static void mov_text_text_cb(void *priv, const char *text, int len)
+{
+    MovTextContext *s = priv;
+    av_strlcpy(s->ptr, text, FFMIN(s->end - s->ptr, len + 1));
+    s->ptr += len;
+}
+
+static void mov_text_new_line_cb(void *priv, int forced)
+{
+    MovTextContext *s = priv;
+    av_strlcpy(s->ptr, "\n", FFMIN(s->end - s->ptr, 2));
+    s->ptr++;
+}
+
+static const ASSCodesCallbacks mov_text_callbacks = {
+    .text     = mov_text_text_cb,
+    .new_line = mov_text_new_line_cb,
+};
+
+static int mov_text_encode_frame(AVCodecContext *avctx, unsigned char *buf,
+                                 int bufsize, void *data)
+{
+    MovTextContext *s = avctx->priv_data;
+    AVSubtitle *sub = data;
+    ASSDialog *dialog;
+    int i, len, num;
+
+    s->ptr = s->buffer;
+    s->end = s->ptr + sizeof(s->buffer);
+
+    for (i = 0; i < sub->num_rects; i++) {
+
+        if (sub->rects[i]->type != SUBTITLE_ASS) {
+            av_log(avctx, AV_LOG_ERROR, "Only SUBTITLE_ASS type supported.\n");
+            return AVERROR(ENOSYS);
+        }
+
+        dialog = ff_ass_split_dialog(s->ass_ctx, sub->rects[i]->ass, 0, &num);
+        for (; dialog && num--; dialog++) {
+            ff_ass_split_override_codes(&mov_text_callbacks, s, dialog->text);
+        }
+    }
+
+    if (s->ptr == s->buffer)
+        return 0;
+
+    AV_WB16(buf, strlen(s->buffer));
+    buf += 2;
+
+    len = av_strlcpy(buf, s->buffer, bufsize - 2);
+
+    if (len > bufsize-3) {
+        av_log(avctx, AV_LOG_ERROR, "Buffer too small for ASS event.\n");
+        return AVERROR(EINVAL);
+    }
+
+    return len + 2;
+}
+
+static int mov_text_encode_close(AVCodecContext *avctx)
+{
+    MovTextContext *s = avctx->priv_data;
+    ff_ass_split_free(s->ass_ctx);
+    return 0;
+}
+
+AVCodec ff_movtext_encoder = {
+    .name           = "mov_text",
+    .long_name      = NULL_IF_CONFIG_SMALL("3GPP Timed Text subtitle"),
+    .type           = AVMEDIA_TYPE_SUBTITLE,
+    .id             = CODEC_ID_MOV_TEXT,
+    .priv_data_size = sizeof(MovTextContext),
+    .init           = mov_text_encode_init,
+    .encode         = mov_text_encode_frame,
+    .close          = mov_text_encode_close,
+};