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* Wing Commander/Xan Video Decoder
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* Copyright (C) 2003 the ffmpeg project
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* This library 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 of the License, or (at your option) any later version.
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* This library 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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* You should have received a copy of the GNU Lesser General Public
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* License along with this library; 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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* Xan video decoder for Wing Commander III computer game
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* by Mario Brito (mbrito@student.dei.uc.pt)
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* and Mike Melanson (melanson@pcisys.net)
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* The xan_wc3 decoder outputs PAL8 data.
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typedef struct XanContext {
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AVCodecContext *avctx;
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AVFrame current_frame;
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unsigned char *buffer1;
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unsigned char *buffer2;
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static int xan_decode_init(AVCodecContext *avctx)
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XanContext *s = avctx->priv_data;
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if ((avctx->codec->id == CODEC_ID_XAN_WC3) &&
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(s->avctx->palctrl == NULL)) {
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av_log(avctx, AV_LOG_ERROR, " WC3 Xan video: palette expected.\n");
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avctx->pix_fmt = PIX_FMT_PAL8;
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avctx->has_b_frames = 0;
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if(avcodec_check_dimensions(avctx, avctx->width, avctx->height))
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s->buffer1_size = avctx->width * avctx->height;
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s->buffer1 = av_malloc(s->buffer1_size);
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s->buffer2_size = avctx->width * avctx->height;
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s->buffer2 = av_malloc(s->buffer2_size);
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if (!s->buffer1 || !s->buffer2)
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/* This function is used in lieu of memcpy(). This decoder can not use
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* memcpy because the memory locations often overlap and
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* memcpy doesn't like that; it's not uncommon, for example, for
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* dest = src+1, to turn byte A into pattern AAAAAAAA.
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* This was originally repz movsb in Intel x86 ASM. */
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static inline void bytecopy(unsigned char *dest, unsigned char *src, int count)
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for (i = 0; i < count; i++)
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static int xan_huffman_decode(unsigned char *dest, unsigned char *src,
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unsigned char byte = *src++;
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unsigned char ival = byte + 0x16;
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unsigned char * ptr = src + byte*2;
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unsigned char val = ival;
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unsigned char *dest_end = dest + dest_len;
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unsigned char bits = *ptr++;
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while ( val != 0x16 ) {
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if ( (1 << counter) & bits )
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val = src[byte + val - 0x17];
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val = src[val - 0x17];
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if (dest + 1 > dest_end)
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if (counter++ == 7) {
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static void xan_unpack(unsigned char *dest, unsigned char *src, int dest_len)
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unsigned char opcode;
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int byte1, byte2, byte3;
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unsigned char *dest_end = dest + dest_len;
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if ( (opcode & 0x80) == 0 ) {
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if (dest + size > dest_end)
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bytecopy(dest, src, size); dest += size; src += size;
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size = ((opcode & 0x1c) >> 2) + 3;
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if (dest + size > dest_end)
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bytecopy (dest, dest - (((opcode & 0x60) << 3) + offset + 1), size);
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} else if ( (opcode & 0x40) == 0 ) {
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if (dest + size > dest_end)
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bytecopy (dest, src, size); dest += size; src += size;
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size = (opcode & 0x3f) + 4;
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if (dest + size > dest_end)
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bytecopy (dest, dest - (((byte1 & 0x3f) << 8) + byte2 + 1), size);
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} else if ( (opcode & 0x20) == 0 ) {
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if (dest + size > dest_end)
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bytecopy (dest, src, size); dest += size; src += size;
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size = byte3 + 5 + ((opcode & 0xc) << 6);
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if (dest + size > dest_end)
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dest - ((((opcode & 0x10) >> 4) << 0x10) + 1 + (byte1 << 8) + byte2),
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size = ((opcode & 0x1f) << 2) + 4;
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if (dest + size > dest_end)
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bytecopy (dest, src, size); dest += size; src += size;
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bytecopy(dest, src, size); dest += size; src += size;
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static void inline xan_wc3_output_pixel_run(XanContext *s,
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unsigned char *pixel_buffer, int x, int y, int pixel_count)
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int width = s->avctx->width;
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unsigned char *palette_plane;
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palette_plane = s->current_frame.data[0];
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stride = s->current_frame.linesize[0];
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line_inc = stride - width;
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index = y * stride + x;
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while((pixel_count--) && (index < s->frame_size)) {
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/* don't do a memcpy() here; keyframes generally copy an entire
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* frame of data and the stride needs to be accounted for */
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palette_plane[index++] = *pixel_buffer++;
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if (current_x >= width) {
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static void inline xan_wc3_copy_pixel_run(XanContext *s,
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int x, int y, int pixel_count, int motion_x, int motion_y)
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int curframe_index, prevframe_index;
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int curframe_x, prevframe_x;
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int width = s->avctx->width;
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unsigned char *palette_plane, *prev_palette_plane;
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palette_plane = s->current_frame.data[0];
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prev_palette_plane = s->last_frame.data[0];
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stride = s->current_frame.linesize[0];
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line_inc = stride - width;
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curframe_index = y * stride + x;
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prevframe_index = (y + motion_y) * stride + x + motion_x;
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prevframe_x = x + motion_x;
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while((pixel_count--) && (curframe_index < s->frame_size)) {
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palette_plane[curframe_index++] =
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prev_palette_plane[prevframe_index++];
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if (curframe_x >= width) {
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curframe_index += line_inc;
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if (prevframe_x >= width) {
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prevframe_index += line_inc;
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static void xan_wc3_decode_frame(XanContext *s) {
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int width = s->avctx->width;
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int height = s->avctx->height;
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int total_pixels = width * height;
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unsigned char opcode;
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unsigned char flag = 0;
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int motion_x, motion_y;
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unsigned char *opcode_buffer = s->buffer1;
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int opcode_buffer_size = s->buffer1_size;
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unsigned char *imagedata_buffer = s->buffer2;
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int imagedata_buffer_size = s->buffer2_size;
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/* pointers to segments inside the compressed chunk */
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unsigned char *huffman_segment;
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unsigned char *size_segment;
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unsigned char *vector_segment;
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unsigned char *imagedata_segment;
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huffman_segment = s->buf + LE_16(&s->buf[0]);
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size_segment = s->buf + LE_16(&s->buf[2]);
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vector_segment = s->buf + LE_16(&s->buf[4]);
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imagedata_segment = s->buf + LE_16(&s->buf[6]);
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xan_huffman_decode(opcode_buffer, huffman_segment, opcode_buffer_size);
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if (imagedata_segment[0] == 2)
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xan_unpack(imagedata_buffer, &imagedata_segment[1],
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imagedata_buffer_size);
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imagedata_buffer = &imagedata_segment[1];
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/* use the decoded data segments to build the frame */
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while (total_pixels) {
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opcode = *opcode_buffer++;
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size += (opcode - 10);
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size = *size_segment++;
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size = BE_16(&size_segment[0]);
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size = (size_segment[0] << 16) | (size_segment[1] << 8) |
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/* run of (size) pixels is unchanged from last frame */
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xan_wc3_copy_pixel_run(s, x, y, size, 0, 0);
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/* output a run of pixels from imagedata_buffer */
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xan_wc3_output_pixel_run(s, imagedata_buffer, x, y, size);
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imagedata_buffer += size;
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/* run-based motion compensation from last frame */
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motion_x = (*vector_segment >> 4) & 0xF;
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motion_y = *vector_segment & 0xF;
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motion_x |= 0xFFFFFFF0;
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motion_y |= 0xFFFFFFF0;
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/* copy a run of pixels from the previous frame */
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xan_wc3_copy_pixel_run(s, x, y, size, motion_x, motion_y);
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/* coordinate accounting */
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total_pixels -= size;
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if (x + size >= width) {
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static void xan_wc4_decode_frame(XanContext *s) {
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static int xan_decode_frame(AVCodecContext *avctx,
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void *data, int *data_size,
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uint8_t *buf, int buf_size)
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XanContext *s = avctx->priv_data;
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AVPaletteControl *palette_control = avctx->palctrl;
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if (avctx->get_buffer(avctx, &s->current_frame)) {
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av_log(s->avctx, AV_LOG_ERROR, " Xan Video: get_buffer() failed\n");
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s->current_frame.reference = 3;
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s->frame_size = s->current_frame.linesize[0] * s->avctx->height;
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palette_control->palette_changed = 0;
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memcpy(s->current_frame.data[1], palette_control->palette,
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s->current_frame.palette_has_changed = 1;
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if (avctx->codec->id == CODEC_ID_XAN_WC3)
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xan_wc3_decode_frame(s);
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else if (avctx->codec->id == CODEC_ID_XAN_WC4)
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xan_wc4_decode_frame(s);
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/* release the last frame if it is allocated */
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if (s->last_frame.data[0])
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avctx->release_buffer(avctx, &s->last_frame);
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s->last_frame = s->current_frame;
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*data_size = sizeof(AVFrame);
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*(AVFrame*)data = s->current_frame;
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/* always report that the buffer was completely consumed */
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static int xan_decode_end(AVCodecContext *avctx)
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XanContext *s = avctx->priv_data;
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/* release the last frame */
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if (s->last_frame.data[0])
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avctx->release_buffer(avctx, &s->last_frame);
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AVCodec xan_wc3_decoder = {
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AVCodec xan_wc4_decoder = {