summaryrefslogtreecommitdiff
path: root/libavcodec/mpeg4_unpack_bframes_bsf.c (plain)
blob: e227f58ec6df6b314b556757965743166490bf2b
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 "bsf.h"
24#include "mpeg4video.h"
25
26typedef struct UnpackBFramesBSFContext {
27 uint8_t *b_frame_buf;
28 int b_frame_buf_size;
29} UnpackBFramesBSFContext;
30
31/* search next start code */
32static 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 */
49static 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 */
75static 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
86static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *out)
87{
88 UnpackBFramesBSFContext *s = ctx->priv_data;
89 int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
90 AVPacket *in;
91
92 ret = ff_bsf_get_packet(ctx, &in);
93 if (ret < 0)
94 return ret;
95
96 scan_buffer(in->data, in->size, &pos_p, &nb_vop, &pos_vop2);
97 av_log(ctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
98
99 if (pos_vop2 >= 0) {
100 if (s->b_frame_buf) {
101 av_log(ctx, AV_LOG_WARNING,
102 "Missing one N-VOP packet, discarding one B-frame.\n");
103 av_freep(&s->b_frame_buf);
104 s->b_frame_buf_size = 0;
105 }
106 /* store the packed B-frame in the BSFContext */
107 s->b_frame_buf_size = in->size - pos_vop2;
108 s->b_frame_buf = create_new_buffer(in->data + pos_vop2, s->b_frame_buf_size);
109 if (!s->b_frame_buf) {
110 s->b_frame_buf_size = 0;
111 av_packet_free(&in);
112 return AVERROR(ENOMEM);
113 }
114 }
115
116 if (nb_vop > 2) {
117 av_log(ctx, AV_LOG_WARNING,
118 "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
119 }
120
121 if (nb_vop == 1 && s->b_frame_buf) {
122 /* use frame from BSFContext */
123 ret = av_packet_copy_props(out, in);
124 if (ret < 0) {
125 av_packet_free(&in);
126 return ret;
127 }
128
129 ret = av_packet_from_data(out, s->b_frame_buf, s->b_frame_buf_size);
130 if (ret < 0) {
131 av_packet_free(&in);
132 return ret;
133 }
134 if (in->size <= MAX_NVOP_SIZE) {
135 /* N-VOP */
136 av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
137 s->b_frame_buf = NULL;
138 s->b_frame_buf_size = 0;
139 } else {
140 /* copy packet into BSFContext */
141 s->b_frame_buf_size = in->size;
142 s->b_frame_buf = create_new_buffer(in->data, in->size);
143 if (!s->b_frame_buf) {
144 s->b_frame_buf_size = 0;
145 av_packet_unref(out);
146 av_packet_free(&in);
147 return AVERROR(ENOMEM);
148 }
149 }
150 } else if (nb_vop >= 2) {
151 /* use first frame of the packet */
152 av_packet_move_ref(out, in);
153 out->size = pos_vop2;
154 } else if (pos_p >= 0) {
155 av_log(ctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
156 av_packet_move_ref(out, in);
157 /* remove 'p' (packed) from the end of the (DivX) userdata string */
158 out->data[pos_p] = '\0';
159 } else {
160 /* copy packet */
161 av_packet_move_ref(out, in);
162 }
163
164 av_packet_free(&in);
165
166 return 0;
167}
168
169static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
170{
171 if (ctx->par_in->extradata) {
172 int pos_p_ext = -1;
173 scan_buffer(ctx->par_in->extradata, ctx->par_in->extradata_size, &pos_p_ext, NULL, NULL);
174 if (pos_p_ext >= 0) {
175 av_log(ctx, AV_LOG_DEBUG,
176 "Updating DivX userdata (remove trailing 'p') in extradata.\n");
177 ctx->par_out->extradata[pos_p_ext] = '\0';
178 }
179 }
180
181 return 0;
182}
183
184static void mpeg4_unpack_bframes_close(AVBSFContext *bsfc)
185{
186 UnpackBFramesBSFContext *ctx = bsfc->priv_data;
187 av_freep(&ctx->b_frame_buf);
188}
189
190static const enum AVCodecID codec_ids[] = {
191 AV_CODEC_ID_MPEG4, AV_CODEC_ID_NONE,
192};
193
194const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {
195 .name = "mpeg4_unpack_bframes",
196 .priv_data_size = sizeof(UnpackBFramesBSFContext),
197 .init = mpeg4_unpack_bframes_init,
198 .filter = mpeg4_unpack_bframes_filter,
199 .close = mpeg4_unpack_bframes_close,
200 .codec_ids = codec_ids,
201};
202
generated by cgit at 2024-05-17 06:57:53 (GMT)