/*
  * Bitstream filter for unpacking DivX-style packed B-frames in MPEG-4 (divx_packed)
  * Copyright (c) 2015 Andreas Cadhalpun <Andreas.Cadhalpun@googlemail.com>
  *
  * 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 "bsf.h"

 #include "mpeg4video.h"
 
 typedef struct UnpackBFramesBSFContext {
     uint8_t *b_frame_buf;
     int      b_frame_buf_size;
 } UnpackBFramesBSFContext;
 
 /* search next start code */
 static unsigned int find_startcode(const uint8_t *buf, int buf_size, int *pos)
 {
     unsigned int startcode = 0xFF;
 
     for (; *pos < buf_size;) {
         startcode = ((startcode << 8) | buf[*pos]) & 0xFFFFFFFF;
         *pos +=1;
         if ((startcode & 0xFFFFFF00) != 0x100)
             continue;  /* no startcode */
         return startcode;
     }
 
     return 0;
 }
 
 /* determine the position of the packed marker in the userdata,
  * the number of VOPs and the position of the second VOP */
 static void scan_buffer(const uint8_t *buf, int buf_size,
                         int *pos_p, int *nb_vop, int *pos_vop2) {
     unsigned int startcode;
     int pos, i;
 
     for (pos = 0; pos < buf_size;) {
         startcode = find_startcode(buf, buf_size, &pos);
 
         if (startcode == USER_DATA_STARTCODE && pos_p) {
             /* check if the (DivX) userdata string ends with 'p' (packed) */
             for (i = 0; i < 255 && pos + i + 1 < buf_size; i++) {
                 if (buf[pos + i] == 'p' && buf[pos + i + 1] == '\0') {
                     *pos_p = pos + i;
                     break;
                 }
             }
         } else if (startcode == VOP_STARTCODE && nb_vop) {
             *nb_vop += 1;
             if (*nb_vop == 2 && pos_vop2) {
                 *pos_vop2 = pos - 4; /* subtract 4 bytes startcode */
             }
         }
     }
 }
 
 /* allocate new buffer and copy size bytes from src */
 static uint8_t *create_new_buffer(const uint8_t *src, int size) {

     uint8_t *dst = av_malloc(size + AV_INPUT_BUFFER_PADDING_SIZE);

 
     if (dst) {
         memcpy(dst, src, size);

         memset(dst + size, 0, AV_INPUT_BUFFER_PADDING_SIZE);

     }
 
     return dst;
 }
 

 static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *out)

 {

     UnpackBFramesBSFContext *s = ctx->priv_data;

     int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;

     AVPacket *in;

     ret = ff_bsf_get_packet(ctx, &in);
     if (ret < 0)
         return ret;

     scan_buffer(in->data, in->size, &pos_p, &nb_vop, &pos_vop2);
     av_log(ctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);

 
     if (pos_vop2 >= 0) {

         if (s->b_frame_buf) {
             av_log(ctx, AV_LOG_WARNING,

                    "Missing one N-VOP packet, discarding one B-frame.\n");

             av_freep(&s->b_frame_buf);
             s->b_frame_buf_size = 0;

         }
         /* store the packed B-frame in the BSFContext */

         s->b_frame_buf_size = in->size - pos_vop2;
         s->b_frame_buf      = create_new_buffer(in->data + pos_vop2, s->b_frame_buf_size);
         if (!s->b_frame_buf) {
             s->b_frame_buf_size = 0;

             ret = AVERROR(ENOMEM);
             goto fail;

         }
     }
 
     if (nb_vop > 2) {

         av_log(ctx, AV_LOG_WARNING,

        "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
     }
 

     if (nb_vop == 1 && s->b_frame_buf) {

         /* use frame from BSFContext */

         ret = av_packet_copy_props(out, in);
         if (ret < 0) {

             goto fail;

         }
 

         ret = av_packet_from_data(out, s->b_frame_buf, s->b_frame_buf_size);
         if (ret < 0) {

             goto fail;

         }

         if (in->size <= MAX_NVOP_SIZE) {

             /* N-VOP */

             av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
             s->b_frame_buf      = NULL;
             s->b_frame_buf_size = 0;

         } else {
             /* copy packet into BSFContext */

             s->b_frame_buf_size = in->size;
             s->b_frame_buf      = create_new_buffer(in->data, in->size);
             if (!s->b_frame_buf) {
                 s->b_frame_buf_size = 0;

                 ret = AVERROR(ENOMEM);
                 goto fail;

             }
         }
     } else if (nb_vop >= 2) {
         /* use first frame of the packet */

         av_packet_move_ref(out, in);
         out->size = pos_vop2;

     } else if (pos_p >= 0) {

         ret = av_packet_make_writable(in);
         if (ret < 0)
             goto fail;

         av_log(ctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
         av_packet_move_ref(out, in);

         /* remove 'p' (packed) from the end of the (DivX) userdata string */

         out->data[pos_p] = '\0';

     } else {
         /* copy packet */

         av_packet_move_ref(out, in);
     }
 

 fail:
     if (ret < 0)
         av_packet_unref(out);

     av_packet_free(&in);
 

     return ret;

 }
 
 static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
 {
     if (ctx->par_in->extradata) {
         int pos_p_ext = -1;
         scan_buffer(ctx->par_in->extradata, ctx->par_in->extradata_size, &pos_p_ext, NULL, NULL);
         if (pos_p_ext >= 0) {
             av_log(ctx, AV_LOG_DEBUG,
                    "Updating DivX userdata (remove trailing 'p') in extradata.\n");
             ctx->par_out->extradata[pos_p_ext] = '\0';
         }

     }
 

     return 0;

 }
 

 static void mpeg4_unpack_bframes_close(AVBSFContext *bsfc)

 {
     UnpackBFramesBSFContext *ctx = bsfc->priv_data;
     av_freep(&ctx->b_frame_buf);
 }
 

 static const enum AVCodecID codec_ids[] = {
     AV_CODEC_ID_MPEG4, AV_CODEC_ID_NONE,
 };
 
 const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {

     .name           = "mpeg4_unpack_bframes",
     .priv_data_size = sizeof(UnpackBFramesBSFContext),

     .init           = mpeg4_unpack_bframes_init,

     .filter         = mpeg4_unpack_bframes_filter,

     .close          = mpeg4_unpack_bframes_close,
     .codec_ids      = codec_ids,

 };