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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 "bsf.h"
#include "mpeg4video.h"
typedef struct UnpackBFramesBSFContext {
AVPacket *b_frame;
} 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 */
}
}
}
}
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->data) {
av_log(ctx, AV_LOG_WARNING,
"Missing one N-VOP packet, discarding one B-frame.\n");
av_packet_unref(s->b_frame);
}
/* store the packed B-frame in the BSFContext */
ret = av_packet_ref(s->b_frame, in);
if (ret < 0) {
goto fail;
}
s->b_frame->size -= pos_vop2;
s->b_frame->data += pos_vop2;
}
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->data) {
/* use frame from BSFContext */
av_packet_move_ref(out, s->b_frame);
/* use properties from current input packet */
ret = av_packet_copy_props(out, in);
if (ret < 0) {
goto fail;
}
if (in->size <= MAX_NVOP_SIZE) {
/* N-VOP */
av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
} else {
/* copy packet into BSFContext */
av_packet_move_ref(s->b_frame, in);
}
} 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)
{
UnpackBFramesBSFContext *s = ctx->priv_data;
s->b_frame = av_packet_alloc();
if (!s->b_frame)
return AVERROR(ENOMEM);
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_packet_free(&ctx->b_frame);
}
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,
};
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