[FFmpeg-devel] [PATCH] movtextdec: MPEG4 Part 17 Timed Text Decoder.

Philip Langdale philipl at overt.org
Wed Jul 4 20:10:32 CEST 2012


This change introduces a basic decoder for MPEG4 Part 17 subtitles,
also known as Timed Text and TX3G.

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

Signed-off-by: Philip Langdale <philipl at overt.org>
---
 Changelog                  |    1 +
 doc/general.texi           |   21 ++++----
 libavcodec/Makefile        |    1 +
 libavcodec/allcodecs.c     |    1 +
 libavcodec/movtextdec.c    |  114 ++++++++++++++++++++++++++++++++++++++++++++
 libavcodec/version.h       |    2 +-
 tests/fate/subtitles.mak   |    3 ++
 tests/ref/fate/sub-movtext |    1 +
 8 files changed, 133 insertions(+), 11 deletions(-)
 create mode 100644 libavcodec/movtextdec.c
 create mode 100644 tests/ref/fate/sub-movtext

diff --git a/Changelog b/Changelog
index a899023..530bd60 100644
--- a/Changelog
+++ b/Changelog
@@ -18,6 +18,7 @@ version next:
 - LucasArts SMUSH playback support
 - SAMI demuxer and decoder
 - RealText demuxer and decoder
+- MPEG4 Part 17 Timed Text decoder
 
 
 version 0.11:
diff --git a/doc/general.texi b/doc/general.texi
index 2ca10cd..9bde6aa 100644
--- a/doc/general.texi
+++ b/doc/general.texi
@@ -858,16 +858,17 @@ performance on systems without hardware floating point support).
 
 @multitable @columnfractions .4 .1 .1 .1 .1
 @item Name @tab Muxing @tab Demuxing @tab Encoding @tab Decoding
- at item SSA/ASS      @tab X @tab X @tab X @tab X
- at item DVB          @tab X @tab X @tab X @tab X
- at item DVD          @tab X @tab X @tab X @tab X
- at item JACOsub      @tab X @tab X @tab   @tab X
- at item MicroDVD     @tab X @tab X @tab   @tab X
- at item PGS          @tab   @tab   @tab   @tab X
- at item RealText     @tab   @tab X @tab   @tab X
- at item SAMI         @tab   @tab X @tab   @tab X
- at item SubRip (SRT) @tab X @tab X @tab X @tab X
- at item XSUB         @tab   @tab   @tab X @tab X
+ at item SSA/ASS          @tab X @tab X @tab X @tab X
+ at item DVB              @tab X @tab X @tab X @tab X
+ at item DVD              @tab X @tab X @tab X @tab X
+ at item JACOsub          @tab X @tab X @tab   @tab X
+ at item MicroDVD         @tab X @tab X @tab   @tab X
+ at item MPEG4 Timed Text @tab   @tab   @tab   @tab X
+ at item PGS              @tab   @tab   @tab   @tab X
+ at item RealText         @tab   @tab X @tab   @tab X
+ at item SAMI             @tab   @tab X @tab   @tab X
+ at item SubRip (SRT)     @tab X @tab X @tab X @tab X
+ at item XSUB             @tab   @tab   @tab X @tab X
 @end multitable
 
 @code{X} means that the feature is supported.
diff --git a/libavcodec/Makefile b/libavcodec/Makefile
index e8fac7e..b613530 100644
--- a/libavcodec/Makefile
+++ b/libavcodec/Makefile
@@ -265,6 +265,7 @@ OBJS-$(CONFIG_MJPEGB_DECODER)          += mjpegbdec.o mjpegdec.o mjpeg.o
 OBJS-$(CONFIG_MLP_DECODER)             += mlpdec.o mlpdsp.o
 OBJS-$(CONFIG_MMVIDEO_DECODER)         += mmvideo.o
 OBJS-$(CONFIG_MOTIONPIXELS_DECODER)    += motionpixels.o
+OBJS-$(CONFIG_MOVTEXT_DECODER)         += movtextdec.o ass.o
 OBJS-$(CONFIG_MP1_DECODER)             += mpegaudiodec.o mpegaudiodecheader.o \
                                           mpegaudio.o mpegaudiodata.o
 OBJS-$(CONFIG_MP1FLOAT_DECODER)        += mpegaudiodec_float.o mpegaudiodecheader.o \
diff --git a/libavcodec/allcodecs.c b/libavcodec/allcodecs.c
index 51e603e..c6216ce 100644
--- a/libavcodec/allcodecs.c
+++ b/libavcodec/allcodecs.c
@@ -404,6 +404,7 @@ void avcodec_register_all(void)
     REGISTER_ENCDEC  (DVDSUB, dvdsub);
     REGISTER_DECODER (JACOSUB, jacosub);
     REGISTER_DECODER (MICRODVD, microdvd);
+    REGISTER_DECODER (MOVTEXT, movtext);
     REGISTER_DECODER (PGSSUB, pgssub);
     REGISTER_DECODER (REALTEXT, realtext);
     REGISTER_DECODER (SAMI, sami);
diff --git a/libavcodec/movtextdec.c b/libavcodec/movtextdec.c
new file mode 100644
index 0000000..63b869d
--- /dev/null
+++ b/libavcodec/movtextdec.c
@@ -0,0 +1,114 @@
+/*
+ * 3GPP TS 26.245/MPEG4 Part 17 Timed Text decoder
+ * Copyright (c) 2012  Philip Langdale <philipl at 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 "avcodec.h"
+#include "ass.h"
+#include "libavutil/avstring.h"
+#include "libavutil/bprint.h"
+#include "libavutil/intreadwrite.h"
+
+static int text_to_ass(AVBPrint *buf, const char *text, const char *text_end)
+{
+    int line_start = 1;
+
+    while (text < text_end) {
+        switch (*text) {
+        case '\r':
+            line_start = 1;
+            break;
+        case '\n':
+            av_bprintf(buf, "\\N");
+            line_start = 1;
+            break;
+        case ' ':
+            // 1) Don't transfer leading whitespace
+            // 2) Don't transfer multiple spaces
+            // 3) Don't transfer trailing whitespace
+            if (!line_start && text + 1 != text_end &&
+                text[1] != ' ' &&
+                text[1] != '\r' && text[1] != '\n')
+                av_bprint_chars(buf, *text, 1);
+            break;
+        default:
+            av_bprint_chars(buf, *text, 1);
+            line_start = 0;
+            break;
+        }
+        text++;
+    }
+
+    av_bprintf(buf, "\r\n");
+    return 0;
+}
+
+static int mov_text_init(AVCodecContext *avctx) {
+    /*
+     * TODO: Handle the default text style.
+     * NB: Most players ignore styles completely, with the result that
+     * it's very common to find files where the default style is broken
+     * and respecting it results in a worse experience than ignoring it.
+     */
+    return ff_ass_subtitle_header_default(avctx);
+}
+
+static int mov_text_decode_frame(AVCodecContext *avctx,
+                            void *data, int *got_sub_ptr, AVPacket *avpkt)
+{
+    AVSubtitle *sub = data;
+    int ts_start, ts_end;
+    AVBPrint buf;
+    const char *ptr = avpkt->data;
+    const char *end;
+
+    if (!ptr || avpkt->size <= 2)
+        return 0;
+
+    /*
+     * The first two bytes of the packet are the length of the text string
+     * In complex cases, there are style descriptors appended to the string
+     * so we can't just assume the packet size is the string size.
+     */
+    end = ptr + 2 + AV_RB16(ptr);
+    ptr += 2;
+
+    ts_start = av_rescale_q(avpkt->pts,
+                            avctx->time_base,
+                            (AVRational){1,100});
+    ts_end   = av_rescale_q(avpkt->pts + avpkt->duration,
+                            avctx->time_base,
+                            (AVRational){1,100});
+
+    av_bprint_init(&buf, 0, 2048);
+    text_to_ass(&buf, ptr, end);
+    ff_ass_add_rect(sub, buf.str, ts_start, ts_end-ts_start, 0);
+    *got_sub_ptr = sub->num_rects > 0;
+    av_bprint_finalize(&buf, NULL);
+    return avpkt->size;
+}
+
+AVCodec ff_movtext_decoder = {
+    .name         = "mov_text",
+    .long_name    = NULL_IF_CONFIG_SMALL("MPEG4 Part 17 subtitle"),
+    .type         = AVMEDIA_TYPE_SUBTITLE,
+    .id           = CODEC_ID_MOV_TEXT,
+    .init         = mov_text_init,
+    .decode       = mov_text_decode_frame,
+};
diff --git a/libavcodec/version.h b/libavcodec/version.h
index 5bfb7f4..275200f 100644
--- a/libavcodec/version.h
+++ b/libavcodec/version.h
@@ -27,7 +27,7 @@
  */
 
 #define LIBAVCODEC_VERSION_MAJOR 54
-#define LIBAVCODEC_VERSION_MINOR  31
+#define LIBAVCODEC_VERSION_MINOR  32
 #define LIBAVCODEC_VERSION_MICRO 100
 
 #define LIBAVCODEC_VERSION_INT  AV_VERSION_INT(LIBAVCODEC_VERSION_MAJOR, \
diff --git a/tests/fate/subtitles.mak b/tests/fate/subtitles.mak
index f2a68e1..92322da 100644
--- a/tests/fate/subtitles.mak
+++ b/tests/fate/subtitles.mak
@@ -13,5 +13,8 @@ fate-sub-srt: CMD = md5 -i $(SAMPLES)/sub/SubRip_capability_tester.srt -f ass
 FATE_SUBTITLES += fate-sub-realtext
 fate-sub-realtext: CMD = md5 -i $(SAMPLES)/sub/RealText_capability_tester.rt -f ass
 
+FATE_SUBTITLES += fate-sub-movtext
+fate-sub-movtext: CMD = md5 -i $(SAMPLES)/sub/MovText_capability_tester.mp4 -f ass
+
 FATE_SAMPLES_FFMPEG += $(FATE_SUBTITLES)
 fate-subtitles: $(FATE_SUBTITLES)
diff --git a/tests/ref/fate/sub-movtext b/tests/ref/fate/sub-movtext
new file mode 100644
index 0000000..d91c243
--- /dev/null
+++ b/tests/ref/fate/sub-movtext
@@ -0,0 +1 @@
+21453e8ddbbe35d1368a99fe563c969d
-- 
1.7.9.5



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