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ffmpeg / libavcodec / xsubenc.c @ 2912e87a

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/*
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 * DivX (XSUB) subtitle encoder
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 * Copyright (c) 2005 DivX, Inc.
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 * Copyright (c) 2009 Bjorn Axelsson
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 *
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 * This file is part of Libav.
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 *
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 * Libav is free software; you can redistribute it and/or
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 * modify it under the terms of the GNU Lesser General Public
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 * License as published by the Free Software Foundation; either
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 * version 2.1 of the License, or (at your option) any later version.
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 *
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 * Libav is distributed in the hope that it will be useful,
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 * but WITHOUT ANY WARRANTY; without even the implied warranty of
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 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
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 * Lesser General Public License for more details.
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 *
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 * You should have received a copy of the GNU Lesser General Public
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 * License along with Libav; if not, write to the Free Software
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 * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
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 */
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#include "avcodec.h"
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#include "bytestream.h"
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#include "put_bits.h"
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/**
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 * Number of pixels to pad left and right.
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 *
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 * The official encoder pads the subtitles with two pixels on either side,
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 * but until we find out why, we won't do it (we will pad to have width
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 * divisible by 2 though).
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 */
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#define PADDING 0
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#define PADDING_COLOR 0
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/**
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 * Encode a single color run. At most 16 bits will be used.
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 * \param len   length of the run, values > 255 mean "until end of line", may not be < 0.
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 * \param color color to encode, only the lowest two bits are used and all others must be 0.
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 */
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static void put_xsub_rle(PutBitContext *pb, int len, int color)
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{
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    if (len <= 255)
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        put_bits(pb, 2 + ((ff_log2_tab[len] >> 1) << 2), len);
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    else
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        put_bits(pb, 14, 0);
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    put_bits(pb, 2, color);
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}
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/**
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 * Encode a 4-color bitmap with XSUB rle.
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 *
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 * The encoded bitmap may be wider than the source bitmap due to padding.
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 */
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static int xsub_encode_rle(PutBitContext *pb, const uint8_t *bitmap,
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                           int linesize, int w, int h)
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{
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    int x0, x1, y, len, color = PADDING_COLOR;
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    for (y = 0; y < h; y++) {
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        x0 = 0;
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        while (x0 < w) {
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            // Make sure we have enough room for at least one run and padding
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            if (pb->size_in_bits - put_bits_count(pb) < 7*8)
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                return -1;
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            x1 = x0;
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            color = bitmap[x1++] & 3;
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            while (x1 < w && (bitmap[x1] & 3) == color)
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                x1++;
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            len = x1 - x0;
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            if (PADDING && x0 == 0) {
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                if (color == PADDING_COLOR) {
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                    len += PADDING;
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                    x0  -= PADDING;
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                } else
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                    put_xsub_rle(pb, PADDING, PADDING_COLOR);
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            }
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            // Run can't be longer than 255, unless it is the rest of a row
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            if (x1 == w && color == PADDING_COLOR) {
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                len += PADDING + (w&1);
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            } else
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                len = FFMIN(len, 255);
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            put_xsub_rle(pb, len, color);
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            x0 += len;
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        }
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        if (color != PADDING_COLOR && (PADDING + (w&1)))
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            put_xsub_rle(pb, PADDING + (w&1), PADDING_COLOR);
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        align_put_bits(pb);
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        bitmap += linesize;
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    }
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    return 0;
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}
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static int make_tc(uint64_t ms, int *tc)
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{
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    static const int tc_divs[3] = { 1000, 60, 60 };
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    int i;
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    for (i=0; i<3; i++) {
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        tc[i] = ms % tc_divs[i];
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        ms /= tc_divs[i];
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    }
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    tc[3] = ms;
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    return ms > 99;
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}
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static int xsub_encode(AVCodecContext *avctx, unsigned char *buf,
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                       int bufsize, void *data)
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{
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    AVSubtitle *h = data;
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    uint64_t startTime = h->pts / 1000; // FIXME: need better solution...
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    uint64_t endTime = startTime + h->end_display_time - h->start_display_time;
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    int start_tc[4], end_tc[4];
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    uint8_t *hdr = buf + 27; // Point behind the timestamp
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    uint8_t *rlelenptr;
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    uint16_t width, height;
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    int i;
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    PutBitContext pb;
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    if (bufsize < 27 + 7*2 + 4*3) {
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        av_log(avctx, AV_LOG_ERROR, "Buffer too small for XSUB header.\n");
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        return -1;
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    }
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    // TODO: support multiple rects
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    if (h->num_rects > 1)
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        av_log(avctx, AV_LOG_WARNING, "Only single rects supported (%d in subtitle.)\n", h->num_rects);
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    // TODO: render text-based subtitles into bitmaps
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    if (!h->rects[0]->pict.data[0] || !h->rects[0]->pict.data[1]) {
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        av_log(avctx, AV_LOG_WARNING, "No subtitle bitmap available.\n");
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        return -1;
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    }
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    // TODO: color reduction, similar to dvdsub encoder
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    if (h->rects[0]->nb_colors > 4)
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        av_log(avctx, AV_LOG_WARNING, "No more than 4 subtitle colors supported (%d found.)\n", h->rects[0]->nb_colors);
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    // TODO: Palette swapping if color zero is not transparent
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    if (((uint32_t *)h->rects[0]->pict.data[1])[0] & 0xff)
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        av_log(avctx, AV_LOG_WARNING, "Color index 0 is not transparent. Transparency will be messed up.\n");
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    if (make_tc(startTime, start_tc) || make_tc(endTime, end_tc)) {
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        av_log(avctx, AV_LOG_WARNING, "Time code >= 100 hours.\n");
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        return -1;
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    }
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    snprintf(buf, 28,
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        "[%02d:%02d:%02d.%03d-%02d:%02d:%02d.%03d]",
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        start_tc[3], start_tc[2], start_tc[1], start_tc[0],
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        end_tc[3],   end_tc[2],   end_tc[1],   end_tc[0]);
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    // Width and height must probably be multiples of 2.
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    // 2 pixels required on either side of subtitle.
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    // Possibly due to limitations of hardware renderers.
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    // TODO: check if the bitmap is already padded
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    width  = FFALIGN(h->rects[0]->w, 2) + PADDING * 2;
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    height = FFALIGN(h->rects[0]->h, 2);
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    bytestream_put_le16(&hdr, width);
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    bytestream_put_le16(&hdr, height);
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    bytestream_put_le16(&hdr, h->rects[0]->x);
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    bytestream_put_le16(&hdr, h->rects[0]->y);
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    bytestream_put_le16(&hdr, h->rects[0]->x + width);
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    bytestream_put_le16(&hdr, h->rects[0]->y + height);
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    rlelenptr = hdr; // Will store length of first field here later.
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    hdr+=2;
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    // Palette
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    for (i=0; i<4; i++)
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        bytestream_put_be24(&hdr, ((uint32_t *)h->rects[0]->pict.data[1])[i]);
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    // Bitmap
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    // RLE buffer. Reserve 2 bytes for possible padding after the last row.
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    init_put_bits(&pb, hdr, bufsize - (hdr - buf) - 2);
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    if (xsub_encode_rle(&pb, h->rects[0]->pict.data[0],
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                        h->rects[0]->pict.linesize[0]*2,
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                        h->rects[0]->w, (h->rects[0]->h + 1) >> 1))
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        return -1;
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    bytestream_put_le16(&rlelenptr, put_bits_count(&pb) >> 3); // Length of first field
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    if (xsub_encode_rle(&pb, h->rects[0]->pict.data[0] + h->rects[0]->pict.linesize[0],
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                        h->rects[0]->pict.linesize[0]*2,
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                        h->rects[0]->w, h->rects[0]->h >> 1))
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        return -1;
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    // Enforce total height to be be multiple of 2
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    if (h->rects[0]->h & 1) {
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        put_xsub_rle(&pb, h->rects[0]->w, PADDING_COLOR);
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        align_put_bits(&pb);
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    }
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    flush_put_bits(&pb);
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    return hdr - buf + put_bits_count(&pb)/8;
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}
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static av_cold int xsub_encoder_init(AVCodecContext *avctx)
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{
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    if (!avctx->codec_tag)
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        avctx->codec_tag = MKTAG('D','X','S','B');
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    return 0;
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}
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AVCodec ff_xsub_encoder = {
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    "xsub",
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    AVMEDIA_TYPE_SUBTITLE,
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    CODEC_ID_XSUB,
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    0,
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    xsub_encoder_init,
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    xsub_encode,
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    NULL,
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    .long_name = NULL_IF_CONFIG_SMALL("DivX subtitles (XSUB)"),
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};