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>
5 * This file is part of FFmpeg.
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.
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.
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
24 #include "mpeg4video.h"
26 typedef struct UnpackBFramesBSFContext {
28 } UnpackBFramesBSFContext;
30 /* search next start code */
31 static unsigned int find_startcode(const uint8_t *buf, int buf_size, int *pos)
33 unsigned int startcode = 0xFF;
35 for (; *pos < buf_size;) {
36 startcode = ((startcode << 8) | buf[*pos]) & 0xFFFFFFFF;
38 if ((startcode & 0xFFFFFF00) != 0x100)
39 continue; /* no startcode */
46 /* determine the position of the packed marker in the userdata,
47 * the number of VOPs and the position of the second VOP */
48 static void scan_buffer(const uint8_t *buf, int buf_size,
49 int *pos_p, int *nb_vop, int *pos_vop2) {
50 unsigned int startcode;
53 for (pos = 0; pos < buf_size;) {
54 startcode = find_startcode(buf, buf_size, &pos);
56 if (startcode == USER_DATA_STARTCODE && pos_p) {
57 /* check if the (DivX) userdata string ends with 'p' (packed) */
58 for (i = 0; i < 255 && pos + i + 1 < buf_size; i++) {
59 if (buf[pos + i] == 'p' && buf[pos + i + 1] == '\0') {
64 } else if (startcode == VOP_STARTCODE && nb_vop) {
66 if (*nb_vop == 2 && pos_vop2) {
67 *pos_vop2 = pos - 4; /* subtract 4 bytes startcode */
73 static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *out)
75 UnpackBFramesBSFContext *s = ctx->priv_data;
76 int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
79 ret = ff_bsf_get_packet(ctx, &in);
83 scan_buffer(in->data, in->size, &pos_p, &nb_vop, &pos_vop2);
84 av_log(ctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
87 if (s->b_frame->data) {
88 av_log(ctx, AV_LOG_WARNING,
89 "Missing one N-VOP packet, discarding one B-frame.\n");
90 av_packet_unref(s->b_frame);
92 /* store the packed B-frame in the BSFContext */
93 ret = av_packet_ref(s->b_frame, in);
97 s->b_frame->size -= pos_vop2;
98 s->b_frame->data += pos_vop2;
102 av_log(ctx, AV_LOG_WARNING,
103 "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
106 if (nb_vop == 1 && s->b_frame->data) {
107 /* use frame from BSFContext */
108 av_packet_move_ref(out, s->b_frame);
110 /* use properties from current input packet */
111 ret = av_packet_copy_props(out, in);
116 if (in->size <= MAX_NVOP_SIZE) {
118 av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
120 /* copy packet into BSFContext */
121 av_packet_move_ref(s->b_frame, in);
123 } else if (nb_vop >= 2) {
124 /* use first frame of the packet */
125 av_packet_move_ref(out, in);
126 out->size = pos_vop2;
127 } else if (pos_p >= 0) {
128 ret = av_packet_make_writable(in);
131 av_log(ctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
132 av_packet_move_ref(out, in);
133 /* remove 'p' (packed) from the end of the (DivX) userdata string */
134 out->data[pos_p] = '\0';
137 av_packet_move_ref(out, in);
142 av_packet_unref(out);
148 static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
150 UnpackBFramesBSFContext *s = ctx->priv_data;
152 s->b_frame = av_packet_alloc();
154 return AVERROR(ENOMEM);
156 if (ctx->par_in->extradata) {
158 scan_buffer(ctx->par_in->extradata, ctx->par_in->extradata_size, &pos_p_ext, NULL, NULL);
159 if (pos_p_ext >= 0) {
160 av_log(ctx, AV_LOG_DEBUG,
161 "Updating DivX userdata (remove trailing 'p') in extradata.\n");
162 ctx->par_out->extradata[pos_p_ext] = '\0';
169 static void mpeg4_unpack_bframes_close(AVBSFContext *bsfc)
171 UnpackBFramesBSFContext *ctx = bsfc->priv_data;
172 av_packet_free(&ctx->b_frame);
175 static const enum AVCodecID codec_ids[] = {
176 AV_CODEC_ID_MPEG4, AV_CODEC_ID_NONE,
179 const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {
180 .name = "mpeg4_unpack_bframes",
181 .priv_data_size = sizeof(UnpackBFramesBSFContext),
182 .init = mpeg4_unpack_bframes_init,
183 .filter = mpeg4_unpack_bframes_filter,
184 .close = mpeg4_unpack_bframes_close,
185 .codec_ids = codec_ids,