[FFmpeg-devel] [PATCH] Write WebVTT output files

[Matthew Heaney]

This revision creates a WebVTT muxer, that outputs files having the
format described in the following specification:

http://dev.w3.org/html5/webvtt/
---
 libavformat/Makefile     |   1 +
 libavformat/allformats.c |   1 +
 libavformat/webvttenc.c  | 139 +++++++++++++++++++++++++++++++++++++++++++++++
 3 files changed, 141 insertions(+)
 create mode 100644 libavformat/webvttenc.c

diff --git a/libavformat/Makefile b/libavformat/Makefile
index 5438b48..3cb076b 100644
--- a/libavformat/Makefile
+++ b/libavformat/Makefile
@@ -393,6 +393,7 @@ OBJS-$(CONFIG_WEBM_MUXER)                += matroskaenc.o matroska.o \
                                             isom.o avc.o \
                                             flacenc_header.o avlanguage.o wv.o
 OBJS-$(CONFIG_WEBVTT_DEMUXER)            += webvttdec.o subtitles.o
+OBJS-$(CONFIG_WEBVTT_MUXER)              += webvttenc.o subtitles.o
 OBJS-$(CONFIG_WSAUD_DEMUXER)             += westwood_aud.o
 OBJS-$(CONFIG_WSVQA_DEMUXER)             += westwood_vqa.o
 OBJS-$(CONFIG_WTV_DEMUXER)               += wtvdec.o wtv.o asfdec.o asf.o asfcrypt.o \
diff --git a/libavformat/allformats.c b/libavformat/allformats.c
index 6274a75..f947e19 100644
--- a/libavformat/allformats.c
+++ b/libavformat/allformats.c
@@ -293,6 +293,7 @@ void av_register_all(void)
     REGISTER_DEMUXER (WC3,              wc3);
     REGISTER_MUXER   (WEBM,             webm);
     REGISTER_DEMUXER (WEBVTT,           webvtt);
+    REGISTER_MUXER   (WEBVTT,           webvtt);
     REGISTER_DEMUXER (WSAUD,            wsaud);
     REGISTER_DEMUXER (WSVQA,            wsvqa);
     REGISTER_MUXDEMUX(WTV,              wtv);
diff --git a/libavformat/webvttenc.c b/libavformat/webvttenc.c
new file mode 100644
index 0000000..45cdec9
--- /dev/null
+++ b/libavformat/webvttenc.c
@@ -0,0 +1,139 @@
+/*
+ * Copyright (c) 2013 Matthew Heaney
+ *
+ * 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
+ */
+
+/**
+ * @file
+ * WebVTT subtitle muxer
+ * @see http://dev.w3.org/html5/webvtt/
+ */
+
+#include "avformat.h"
+
+typedef struct WebVTTMuxContext {
+    const AVClass *class;
+} WebVTTMuxContext;
+
+static void webvtt_write_time(AVIOContext *pb,
+                              int64_t pts,
+                              const AVRational* time_base)
+{
+    int64_t sec, min, hour;
+    int64_t millisec = (pts * time_base->num * 1000) / time_base->den;
+    sec = millisec / 1000;
+    millisec -= 1000 * sec;
+    min = sec / 60;
+    sec -= 60 * min;
+    hour = min / 60;
+    min -= 60 * hour;
+
+#if 1
+    // TODO(matthewjheaney at google.com): the timestamp parsing in webvttdec.c
+    // is broken, so for now just output a timestamp in the format we can read.
+    avio_printf(pb, "%ld:%02ld:%02ld.%03ld", hour, min, sec, millisec);
+#else
+    if (hour > 0) {
+        avio_printf(pb, "%ld:%02ld:%02ld", hour, min, sec);
+    } else if (min > 0) {
+        avio_printf(pb, "%ld:%02ld", min, sec);
+    } else {
+        avio_printf(pb, "%ld", sec);
+    }
+
+    if (millisec > 0) {
+        avio_printf(pb, ".%03ld", millisec);
+    }
+#endif
+}
+
+static int webvtt_write_header(AVFormatContext *ctx)
+{
+    AVIOContext *pb = ctx->pb;
+    const char header[] = "WEBVTT\n";
+
+    avio_write(pb, header, strlen(header));
+    avio_flush(pb);
+
+    return 0;
+}
+
+static int webvtt_write_packet(AVFormatContext *ctx, AVPacket *pkt)
+{
+    AVStream     *s  = ctx->streams[0];
+    AVIOContext  *pb = ctx->pb;
+    const char space[] = " ";
+    const char EOL[] = "\n";
+    const char arrow[] = "-->";
+    int id_size, settings_size;
+    uint8_t *id, *settings;
+
+    // Write cue separator.
+
+    avio_write(pb, EOL, 1);
+
+    // Write cue id (but only if present).
+
+    id_size = 0;
+    id = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_IDENTIFIER,
+                                 &id_size);
+
+    if (id_size > 0) {
+        avio_write(pb, id, id_size);
+        avio_write(pb, EOL, 1);
+    }
+
+    // Write timestamp and (optional) settings.
+
+    webvtt_write_time(pb, pkt->pts, &s->time_base);
+
+    avio_write(pb, space, strlen(space));
+    avio_write(pb, arrow, strlen(arrow));
+    avio_write(pb, space, strlen(space));
+
+    webvtt_write_time(pb, pkt->pts + pkt->duration, &s->time_base);
+
+    settings_size = 0;
+    settings = av_packet_get_side_data(pkt, AV_PKT_DATA_WEBVTT_SETTINGS,
+                                       &settings_size);
+
+    if (settings_size > 0) {
+        avio_write(pb, space, strlen(space));
+        avio_write(pb, settings, settings_size);
+    }
+
+    avio_write(pb, EOL, 1);
+
+    // Write cue text.
+
+    avio_write(pb, pkt->data, pkt->size);
+    avio_write(pb, EOL, 1);
+
+    return 0;
+}
+
+AVOutputFormat ff_webvtt_muxer = {
+    .name              = "webvtt",
+    .long_name         = NULL_IF_CONFIG_SMALL("WebVTT subtitle"),
+    .extensions        = "vtt",
+    .mime_type         = "text/vtt",
+    .priv_data_size    = sizeof(WebVTTMuxContext),
+    .subtitle_codec    = AV_CODEC_ID_WEBVTT,
+    .write_header      = webvtt_write_header,
+    .write_packet      = webvtt_write_packet,
+};
-- 
1.8.3