lavf: add a real SRT muxer.

This muxer supports CODEC_ID_SRT with the timestamps in the packet data
and CODEC_ID_TEXT with the timestamps in the packet fields.

Makes -scodec copy work from Matroska.

libavformat/Makefile

@@ -313,7 +313,7 @@ OBJS-$(CONFIG_SOX_MUXER)                 += soxenc.o
 OBJS-$(CONFIG_SPDIF_DEMUXER)             += spdif.o spdifdec.o
 OBJS-$(CONFIG_SPDIF_MUXER)               += spdif.o spdifenc.o
 OBJS-$(CONFIG_SRT_DEMUXER)               += srtdec.o
-OBJS-$(CONFIG_SRT_MUXER)                 += rawenc.o
+OBJS-$(CONFIG_SRT_MUXER)                 += srtenc.o
 OBJS-$(CONFIG_STR_DEMUXER)               += psxstr.o
 OBJS-$(CONFIG_SWF_DEMUXER)               += swfdec.o
 OBJS-$(CONFIG_SWF_MUXER)                 += swfenc.o

libavformat/rawenc.c

@@ -257,18 +257,6 @@ AVOutputFormat ff_rawvideo_muxer = {
 };
 #endif
 
-#if CONFIG_SRT_MUXER
-AVOutputFormat ff_srt_muxer = {
-    .name              = "srt",
-    .long_name         = NULL_IF_CONFIG_SMALL("SubRip subtitle format"),
-    .mime_type         = "application/x-subrip",
-    .extensions        = "srt",
-    .write_packet      = ff_raw_write_packet,
-    .flags             = AVFMT_NOTIMESTAMPS,
-    .subtitle_codec    = CODEC_ID_SRT,
-};
-#endif
-
 #if CONFIG_TRUEHD_MUXER
 AVOutputFormat ff_truehd_muxer = {
     .name              = "truehd",

libavformat/srtenc.c

@@ -0,0 +1,99 @@
+/*
+ * SubRip subtitle muxer
+ * Copyright (c) 2012  Nicolas George <nicolas.george@normalesup.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 "avformat.h"
+#include "internal.h"
+#include "libavutil/log.h"
+
+/* TODO: add options for:
+   - character encoding;
+   - LF / CRLF;
+   - byte order mark.
+ */
+
+typedef struct SRTContext{
+    unsigned index;
+} SRTContext;
+
+static int srt_write_header(AVFormatContext *avf)
+{
+    if (avf->nb_streams != 1 ||
+        avf->streams[0]->codec->codec_type != AVMEDIA_TYPE_SUBTITLE) {
+        av_log(avf, AV_LOG_ERROR,
+               "SRT supports only a single subtitles stream.\n");
+        return AVERROR(EINVAL);
+    }
+    if (avf->streams[0]->codec->codec_id != CODEC_ID_TEXT &&
+        avf->streams[0]->codec->codec_id != CODEC_ID_SRT) {
+        av_log(avf, AV_LOG_ERROR,
+               "Unsupported subtitles codec: %s\n",
+               avcodec_get_name(avf->streams[0]->codec->codec_id));
+        return AVERROR(EINVAL);
+    }
+    avpriv_set_pts_info(avf->streams[0], 64, 1, 1000);
+    return 0;
+}
+
+static int srt_write_packet(AVFormatContext *avf, AVPacket *pkt)
+{
+    SRTContext *srt = avf->priv_data;
+    int write_ts = avf->streams[0]->codec->codec_id != CODEC_ID_SRT;
+
+    srt->index++;
+    if (write_ts) {
+        char buf[64];
+        int64_t s = pkt->pts, e, d = pkt->duration;
+        int len;
+
+        if (d <= 0)
+            d = pkt->convergence_duration;
+        if (s == AV_NOPTS_VALUE || d <= 0) {
+            av_log(avf, AV_LOG_ERROR, "Insufficient timestamps.\n");
+            return AVERROR(EINVAL);
+        }
+        e = s + d;
+        len = snprintf(buf, sizeof(buf),
+                       "%d\n%02d:%02d:%02d,%03d --> %02d:%02d:%02d,%03d\n",
+                       srt->index,
+                       (int)(s / 3600000),      (int)(s / 60000) % 60,
+                       (int)(s /    1000) % 60, (int)(s %  1000),
+                       (int)(e / 3600000),      (int)(e / 60000) % 60,
+                       (int)(e /    1000) % 60, (int)(e %  1000));
+        avio_write(avf->pb, buf, len);
+    }
+    avio_write(avf->pb, pkt->data, pkt->size);
+    if (write_ts)
+        avio_write(avf->pb, "\n\n", 2);
+    avio_flush(avf->pb);
+    return 0;
+}
+
+AVOutputFormat ff_srt_muxer = {
+    .name           = "srt",
+    .long_name      = NULL_IF_CONFIG_SMALL("SubRip subtitle format"),
+    .mime_type      = "application/x-subrip",
+    .extensions     = "srt",
+    .priv_data_size = sizeof(SRTContext),
+    .write_header   = srt_write_header,
+    .write_packet   = srt_write_packet,
+    .flags          = AVFMT_VARIABLE_FPS,
+    .subtitle_codec = CODEC_ID_TEXT,
+};