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/*
* 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 "mpeg4video.h"
typedef struct UnpackBFramesBSFContext {
uint8_t *b_frame_buf;
int b_frame_buf_size;
int updated_extradata;
} 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(AVBitStreamFilterContext *bsfc,
AVCodecContext *avctx, const char *args,
uint8_t **poutbuf, int *poutbuf_size,
const uint8_t *buf, int buf_size,
int keyframe)
{
UnpackBFramesBSFContext *ctx = bsfc->priv_data;
int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
if (avctx->codec_id != AV_CODEC_ID_MPEG4) {
av_log(avctx, AV_LOG_ERROR,
"The mpeg4_unpack_bframes bitstream filter is only useful for mpeg4.\n");
return AVERROR(EINVAL);
}
if (!ctx->updated_extradata && avctx->extradata) {
int pos_p_ext = -1;
scan_buffer(avctx->extradata, avctx->extradata_size, &pos_p_ext, NULL, NULL);
if (pos_p_ext >= 0) {
av_log(avctx, AV_LOG_DEBUG,
"Updating DivX userdata (remove trailing 'p') in extradata.\n");
avctx->extradata[pos_p_ext] = '\0';
}
ctx->updated_extradata = 1;
}
scan_buffer(buf, buf_size, &pos_p, &nb_vop, &pos_vop2);
av_log(avctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
if (pos_vop2 >= 0) {
if (ctx->b_frame_buf) {
av_log(avctx, AV_LOG_WARNING,
"Missing one N-VOP packet, discarding one B-frame.\n");
av_freep(&ctx->b_frame_buf);
ctx->b_frame_buf_size = 0;
}
/* store the packed B-frame in the BSFContext */
ctx->b_frame_buf_size = buf_size - pos_vop2;
ctx->b_frame_buf = create_new_buffer(buf + pos_vop2, ctx->b_frame_buf_size);
if (!ctx->b_frame_buf) {
ctx->b_frame_buf_size = 0;
return AVERROR(ENOMEM);
}
}
if (nb_vop > 2) {
av_log(avctx, AV_LOG_WARNING,
"Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
}
if (nb_vop == 1 && ctx->b_frame_buf) {
/* use frame from BSFContext */
*poutbuf = ctx->b_frame_buf;
*poutbuf_size = ctx->b_frame_buf_size;
/* the output buffer is distinct from the input buffer */
ret = 1;
if (buf_size <= MAX_NVOP_SIZE) {
/* N-VOP */
av_log(avctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
ctx->b_frame_buf = NULL;
ctx->b_frame_buf_size = 0;
} else {
/* copy packet into BSFContext */
ctx->b_frame_buf_size = buf_size;
ctx->b_frame_buf = create_new_buffer(buf , buf_size);
if (!ctx->b_frame_buf) {
ctx->b_frame_buf_size = 0;
av_freep(poutbuf);
*poutbuf_size = 0;
return AVERROR(ENOMEM);
}
}
} else if (nb_vop >= 2) {
/* use first frame of the packet */
*poutbuf = (uint8_t *) buf;
*poutbuf_size = pos_vop2;
} else if (pos_p >= 0) {
av_log(avctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
*poutbuf_size = buf_size;
*poutbuf = create_new_buffer(buf, buf_size);
if (!*poutbuf) {
*poutbuf_size = 0;
return AVERROR(ENOMEM);
}
/* remove 'p' (packed) from the end of the (DivX) userdata string */
(*poutbuf)[pos_p] = '\0';
/* the output buffer is distinct from the input buffer */
ret = 1;
} else {
/* copy packet */
*poutbuf = (uint8_t *) buf;
*poutbuf_size = buf_size;
}
return ret;
}
static void mpeg4_unpack_bframes_close(AVBitStreamFilterContext *bsfc)
{
UnpackBFramesBSFContext *ctx = bsfc->priv_data;
av_freep(&ctx->b_frame_buf);
}
AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {
.name = "mpeg4_unpack_bframes",
.priv_data_size = sizeof(UnpackBFramesBSFContext),
.filter = mpeg4_unpack_bframes_filter,
.close = mpeg4_unpack_bframes_close
};
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