Add support for encoding XSUB subtitles. Muxing support is still missing.

Based on code by DivX, Inc., heavily changed by Björn Axelsson [gecko acc.umu.se] and me.

Originally committed as revision 19222 to svn://svn.ffmpeg.org/ffmpeg/trunk

Changelog

@@ -25,6 +25,7 @@ version <next>:
 - AMR-NB decoding/encoding, AMR-WB decoding via OpenCORE libraries
 - DPX image decoder
 - Electronic Arts Madcow decoder
+- DivX (XSUB) subtitle encoder
 
 
 

doc/general.texi

@@ -648,7 +648,7 @@ performance on systems without hardware floating point support).
 @item SSA/ASS      @tab X @tab X
 @item DVB          @tab X @tab X @tab X @tab X
 @item DVD          @tab X @tab X @tab X @tab X
-@item XSUB         @tab   @tab   @tab   @tab X
+@item XSUB         @tab   @tab   @tab X @tab X
 @end multitable
 
 @code{X} means that the feature is supported.

libavcodec/Makefile

@@ -273,6 +273,7 @@ OBJS-$(CONFIG_XAN_WC3_DECODER)         += xan.o
 OBJS-$(CONFIG_XAN_WC4_DECODER)         += xan.o
 OBJS-$(CONFIG_XL_DECODER)              += xl.o
 OBJS-$(CONFIG_XSUB_DECODER)            += xsubdec.o
+OBJS-$(CONFIG_XSUB_ENCODER)            += xsubenc.o
 OBJS-$(CONFIG_ZLIB_DECODER)            += lcldec.o
 OBJS-$(CONFIG_ZLIB_ENCODER)            += lclenc.o
 OBJS-$(CONFIG_ZMBV_DECODER)            += zmbv.o

libavcodec/allcodecs.c

@@ -301,7 +301,7 @@ void avcodec_register_all(void)
     /* subtitles */
     REGISTER_ENCDEC  (DVBSUB, dvbsub);
     REGISTER_ENCDEC  (DVDSUB, dvdsub);
-    REGISTER_DECODER (XSUB, xsub);
+    REGISTER_ENCDEC  (XSUB, xsub);
 
     /* external libraries */
     REGISTER_ENCDEC  (LIBAMR_NB, libamr_nb);

libavcodec/xsubenc.c

@@ -0,0 +1,222 @@
+/*
+ * DivX (XSUB) subtitle encoder
+ * Copyright (c) 2005 DivX, Inc.
+ * Copyright (c) 2009 Bjorn Axelsson
+ *
+ * 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 "bytestream.h"
+#include "put_bits.h"
+
+/**
+ * Number of pixels to pad left and right.
+ *
+ * The official encoder pads the subtitles with two pixels on either side,
+ * but until we find out why, we won't do it (we will pad to have width
+ * divisible by 2 though).
+ */
+#define PADDING 0
+#define PADDING_COLOR 0
+
+/**
+ * Encodes a single color run. At most 16 bits will be used.
+ * \param len   length of the run, values > 255 mean "until end of line", may not be < 0.
+ * \param color color to encode, only the lowest two bits are used and all others must be 0.
+ */
+static void put_xsub_rle(PutBitContext *pb, int len, int color)
+{
+    if (len <= 255)
+        put_bits(pb, 2 + ((ff_log2_tab[len] >> 1) << 2), len);
+    else
+        put_bits(pb, 14, 0);
+    put_bits(pb, 2, color);
+}
+
+/**
+ * Encodes a 4-color bitmap with XSUB rle.
+ *
+ * The encoded bitmap may be wider than the source bitmap due to padding.
+ */
+static int xsub_encode_rle(PutBitContext *pb, const uint8_t *bitmap,
+                           int linesize, int w, int h)
+{
+    int x0, x1, y, len, color = PADDING_COLOR;
+
+    for (y = 0; y < h; y++) {
+        x0 = 0;
+        while (x0 < w) {
+            // Make sure we have enough room for at least one run and padding
+            if (pb->size_in_bits - put_bits_count(pb) < 7*8)
+                return -1;
+
+            x1 = x0;
+            color = bitmap[x1++] & 3;
+            while (x1 < w && (bitmap[x1] & 3) == color)
+                x1++;
+            len = x1 - x0;
+            if (PADDING && x0 == 0) {
+                if (color == PADDING_COLOR) {
+                    len += PADDING;
+                    x0  -= PADDING;
+                } else
+                    put_xsub_rle(pb, PADDING, PADDING_COLOR);
+            }
+
+            // Run can't be longer than 255, unless it is the rest of a row
+            if (x1 == w && color == PADDING_COLOR) {
+                len += PADDING + (w&1);
+            } else
+                len = FFMIN(len, 255);
+            put_xsub_rle(pb, len, color);
+
+            x0 += len;
+        }
+        if (color != PADDING_COLOR && (PADDING + (w&1)))
+            put_xsub_rle(pb, PADDING + (w&1), PADDING_COLOR);
+
+        align_put_bits(pb);
+
+        bitmap += linesize;
+    }
+
+    return 0;
+}
+
+static int make_tc(uint64_t ms, int *tc)
+{
+    static const int tc_divs[3] = { 1000, 60, 60 };
+    int i;
+    for (i=0; i<3; i++) {
+        tc[i] = ms % tc_divs[i];
+        ms /= tc_divs[i];
+    }
+    tc[3] = ms;
+    return ms > 99;
+}
+
+static int xsub_encode(AVCodecContext *avctx, unsigned char *buf,
+                       int bufsize, void *data)
+{
+    AVSubtitle *h = data;
+    uint64_t startTime = h->pts / 1000; // FIXME: need better solution...
+    uint64_t endTime = startTime + h->end_display_time - h->start_display_time;
+    int start_tc[4], end_tc[4];
+    uint8_t *hdr = buf + 27; // Point behind the timestamp
+    uint8_t *rlelenptr;
+    uint16_t width, height;
+    int i;
+    PutBitContext pb;
+
+    if (bufsize < 27 + 7*2 + 4*3) {
+        av_log(avctx, AV_LOG_ERROR, "Buffer too small for XSUB header.\n");
+        return -1;
+    }
+
+    // TODO: support multiple rects
+    if (h->num_rects > 1)
+        av_log(avctx, AV_LOG_WARNING, "Only single rects supported (%d in subtitle.)\n", h->num_rects);
+
+    // TODO: render text-based subtitles into bitmaps
+    if (!h->rects[0]->pict.data[0] || !h->rects[0]->pict.data[1]) {
+        av_log(avctx, AV_LOG_WARNING, "No subtitle bitmap available.\n");
+        return -1;
+    }
+
+    // TODO: color reduction, similar to dvdsub encoder
+    if (h->rects[0]->nb_colors > 4)
+        av_log(avctx, AV_LOG_WARNING, "No more than 4 subtitle colors supported (%d found.)\n", h->rects[0]->nb_colors);
+
+    // TODO: Palette swapping if color zero is not transparent
+    if (((uint32_t *)h->rects[0]->pict.data[1])[0] & 0xff)
+        av_log(avctx, AV_LOG_WARNING, "Color index 0 is not transparent. Transparency will be messed up.\n");
+
+    if (make_tc(startTime, start_tc) || make_tc(endTime, end_tc)) {
+        av_log(avctx, AV_LOG_WARNING, "Time code >= 100 hours.\n");
+        return -1;
+    }
+
+    snprintf(buf, 28,
+        "[%02d:%02d:%02d.%03d-%02d:%02d:%02d.%03d]",
+        start_tc[3], start_tc[2], start_tc[1], start_tc[0],
+        end_tc[3],   end_tc[3],   end_tc[1],   end_tc[0]);
+
+    // Width and height must probably be multiples of 2.
+    // 2 pixels required on either side of subtitle.
+    // Possibly due to limitations of hardware renderers.
+    // TODO: check if the bitmap is already padded
+    width  = FFALIGN(h->rects[0]->w, 2) + PADDING * 2;
+    height = FFALIGN(h->rects[0]->h, 2);
+
+    bytestream_put_le16(&hdr, width);
+    bytestream_put_le16(&hdr, height);
+    bytestream_put_le16(&hdr, h->rects[0]->x);
+    bytestream_put_le16(&hdr, h->rects[0]->y);
+    bytestream_put_le16(&hdr, h->rects[0]->x + width);
+    bytestream_put_le16(&hdr, h->rects[0]->y + height);
+
+    rlelenptr = hdr; // Will store length of first field here later.
+    hdr+=2;
+
+    // Palette
+    for (i=0; i<4; i++)
+        bytestream_put_be24(&hdr, ((uint32_t *)h->rects[0]->pict.data[1])[i]);
+
+    // Bitmap
+    // RLE buffer. Reserve 2 bytes for possible padding after the last row.
+    init_put_bits(&pb, hdr, bufsize - (hdr - buf) - 2);
+    if (xsub_encode_rle(&pb, h->rects[0]->pict.data[0],
+                        h->rects[0]->pict.linesize[0]*2,
+                        h->rects[0]->w, (h->rects[0]->h + 1) >> 1))
+        return -1;
+    bytestream_put_le16(&rlelenptr, put_bits_count(&pb) >> 3); // Length of first field
+
+    if (xsub_encode_rle(&pb, h->rects[0]->pict.data[0] + h->rects[0]->pict.linesize[0],
+                        h->rects[0]->pict.linesize[0]*2,
+                        h->rects[0]->w, h->rects[0]->h >> 1))
+        return -1;
+
+    // Enforce total height to be be multiple of 2
+    if (h->rects[0]->h & 1) {
+        put_xsub_rle(&pb, h->rects[0]->w, PADDING_COLOR);
+        align_put_bits(&pb);
+    }
+
+    flush_put_bits(&pb);
+
+    return hdr - buf + put_bits_count(&pb)/8;
+}
+
+static av_cold int xsub_encoder_init(AVCodecContext *avctx)
+{
+    if (!avctx->codec_tag)
+        avctx->codec_tag = MKTAG('D','X','S','B');
+
+    return 0;
+}
+
+AVCodec xsub_encoder = {
+    "xsub",
+    CODEC_TYPE_SUBTITLE,
+    CODEC_ID_XSUB,
+    0,
+    xsub_encoder_init,
+    xsub_encode,
+    NULL,
+    .long_name = NULL_IF_CONFIG_SMALL("DivX subtitles (XSUB)"),
+};