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  1. /*
  2.  * Bitstream filter for unpacking DivX-style packed B-frames in MPEG-4 (divx_packed)
  3.  * Copyright (c) 2015 Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
  4.  *
  5.  * This file is part of FFmpeg.
  6.  *
  7.  * FFmpeg is free software; you can redistribute it and/or
  8.  * modify it under the terms of the GNU Lesser General Public
  9.  * License as published by the Free Software Foundation; either
  10.  * version 2.1 of the License, or (at your option) any later version.
  11.  *
  12.  * FFmpeg is distributed in the hope that it will be useful,
  13.  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  14.  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15.  * Lesser General Public License for more details.
  16.  *
  17.  * You should have received a copy of the GNU Lesser General Public
  18.  * License along with FFmpeg; if not, write to the Free Software
  19.  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
  20.  */
  21.  
  22. #include "avcodec.h"
  23. #include "mpeg4video.h"
  24.  
  25. typedef struct UnpackBFramesBSFContext {
  26.     uint8_t *b_frame_buf;
  27.     int      b_frame_buf_size;
  28.     int      updated_extradata;
  29. } UnpackBFramesBSFContext;
  30.  
  31. /* search next start code */
  32. static unsigned int find_startcode(const uint8_t *buf, int buf_size, int *pos)
  33. {
  34.     unsigned int startcode = 0xFF;
  35.  
  36.     for (; *pos < buf_size;) {
  37.         startcode = ((startcode << 8) | buf[*pos]) & 0xFFFFFFFF;
  38.         *pos +=1;
  39.         if ((startcode & 0xFFFFFF00) != 0x100)
  40.             continue;  /* no startcode */
  41.         return startcode;
  42.     }
  43.  
  44.     return 0;
  45. }
  46.  
  47. /* determine the position of the packed marker in the userdata,
  48.  * the number of VOPs and the position of the second VOP */
  49. static void scan_buffer(const uint8_t *buf, int buf_size,
  50.                         int *pos_p, int *nb_vop, int *pos_vop2) {
  51.     unsigned int startcode;
  52.     int pos, i;
  53.  
  54.     for (pos = 0; pos < buf_size;) {
  55.         startcode = find_startcode(buf, buf_size, &pos);
  56.  
  57.         if (startcode == USER_DATA_STARTCODE && pos_p) {
  58.             /* check if the (DivX) userdata string ends with 'p' (packed) */
  59.             for (i = 0; i < 255 && pos + i + 1 < buf_size; i++) {
  60.                 if (buf[pos + i] == 'p' && buf[pos + i + 1] == '\0') {
  61.                     *pos_p = pos + i;
  62.                     break;
  63.                 }
  64.             }
  65.         } else if (startcode == VOP_STARTCODE && nb_vop) {
  66.             *nb_vop += 1;
  67.             if (*nb_vop == 2 && pos_vop2) {
  68.                 *pos_vop2 = pos - 4; /* subtract 4 bytes startcode */
  69.             }
  70.         }
  71.     }
  72. }
  73.  
  74. /* allocate new buffer and copy size bytes from src */
  75. static uint8_t *create_new_buffer(const uint8_t *src, int size) {
  76.     uint8_t *dst = av_malloc(size + AV_INPUT_BUFFER_PADDING_SIZE);
  77.  
  78.     if (dst) {
  79.         memcpy(dst, src, size);
  80.         memset(dst + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);
  81.     }
  82.  
  83.     return dst;
  84. }
  85.  
  86. static int mpeg4_unpack_bframes_filter(AVBitStreamFilterContext *bsfc,
  87.                                        AVCodecContext *avctx, const char *args,
  88.                                        uint8_t  **poutbuf, int *poutbuf_size,
  89.                                        const uint8_t *buf, int      buf_size,
  90.                                        int keyframe)
  91. {
  92.     UnpackBFramesBSFContext *ctx = bsfc->priv_data;
  93.     int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
  94.  
  95.     if (avctx->codec_id != AV_CODEC_ID_MPEG4) {
  96.         av_log(avctx, AV_LOG_ERROR,
  97.                "The mpeg4_unpack_bframes bitstream filter is only useful for mpeg4.\n");
  98.         return AVERROR(EINVAL);
  99.     }
  100.  
  101.     if (!ctx->updated_extradata && avctx->extradata) {
  102.         int pos_p_ext = -1;
  103.         scan_buffer(avctx->extradata, avctx->extradata_size, &pos_p_ext, NULL, NULL);
  104.         if (pos_p_ext >= 0) {
  105.             av_log(avctx, AV_LOG_DEBUG,
  106.                    "Updating DivX userdata (remove trailing 'p') in extradata.\n");
  107.             avctx->extradata[pos_p_ext] = '\0';
  108.         }
  109.         ctx->updated_extradata = 1;
  110.     }
  111.  
  112.     scan_buffer(buf, buf_size, &pos_p, &nb_vop, &pos_vop2);
  113.     av_log(avctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
  114.  
  115.     if (pos_vop2 >= 0) {
  116.         if (ctx->b_frame_buf) {
  117.             av_log(avctx, AV_LOG_WARNING,
  118.                    "Missing one N-VOP packet, discarding one B-frame.\n");
  119.             av_freep(&ctx->b_frame_buf);
  120.             ctx->b_frame_buf_size = 0;
  121.         }
  122.         /* store the packed B-frame in the BSFContext */
  123.         ctx->b_frame_buf_size = buf_size - pos_vop2;
  124.         ctx->b_frame_buf      = create_new_buffer(buf + pos_vop2, ctx->b_frame_buf_size);
  125.         if (!ctx->b_frame_buf) {
  126.             ctx->b_frame_buf_size = 0;
  127.             return AVERROR(ENOMEM);
  128.         }
  129.     }
  130.  
  131.     if (nb_vop > 2) {
  132.         av_log(avctx, AV_LOG_WARNING,
  133.        "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
  134.     }
  135.  
  136.     if (nb_vop == 1 && ctx->b_frame_buf) {
  137.         /* use frame from BSFContext */
  138.         *poutbuf      = ctx->b_frame_buf;
  139.         *poutbuf_size = ctx->b_frame_buf_size;
  140.         /* the output buffer is distinct from the input buffer */
  141.         ret = 1;
  142.         if (buf_size <= MAX_NVOP_SIZE) {
  143.             /* N-VOP */
  144.             av_log(avctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
  145.             ctx->b_frame_buf      = NULL;
  146.             ctx->b_frame_buf_size = 0;
  147.         } else {
  148.             /* copy packet into BSFContext */
  149.             ctx->b_frame_buf_size = buf_size;
  150.             ctx->b_frame_buf      = create_new_buffer(buf , buf_size);
  151.             if (!ctx->b_frame_buf) {
  152.                 ctx->b_frame_buf_size = 0;
  153.                 av_freep(poutbuf);
  154.                 *poutbuf_size = 0;
  155.                 return AVERROR(ENOMEM);
  156.             }
  157.         }
  158.     } else if (nb_vop >= 2) {
  159.         /* use first frame of the packet */
  160.         *poutbuf      = (uint8_t *) buf;
  161.         *poutbuf_size = pos_vop2;
  162.     } else if (pos_p >= 0) {
  163.         av_log(avctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
  164.         *poutbuf_size = buf_size;
  165.         *poutbuf      = create_new_buffer(buf, buf_size);
  166.         if (!*poutbuf) {
  167.             *poutbuf_size = 0;
  168.             return AVERROR(ENOMEM);
  169.         }
  170.         /* remove 'p' (packed) from the end of the (DivX) userdata string */
  171.         (*poutbuf)[pos_p] = '\0';
  172.         /* the output buffer is distinct from the input buffer */
  173.         ret = 1;
  174.     } else {
  175.         /* copy packet */
  176.         *poutbuf      = (uint8_t *) buf;
  177.         *poutbuf_size = buf_size;
  178.     }
  179.  
  180.     return ret;
  181. }
  182.  
  183. static void mpeg4_unpack_bframes_close(AVBitStreamFilterContext *bsfc)
  184. {
  185.     UnpackBFramesBSFContext *ctx = bsfc->priv_data;
  186.     av_freep(&ctx->b_frame_buf);
  187. }
  188.  
  189. AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {
  190.     .name           = "mpeg4_unpack_bframes",
  191.     .priv_data_size = sizeof(UnpackBFramesBSFContext),
  192.     .filter         = mpeg4_unpack_bframes_filter,
  193.     .close          = mpeg4_unpack_bframes_close
  194. };
  195.