FFmpeg
mpeg4_unpack_bframes_bsf.c
Go to the documentation of this file.
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 "internal.h"
25 #include "mpeg4video.h"
26 
27 typedef struct UnpackBFramesBSFContext {
30 
31 /* determine the position of the packed marker in the userdata,
32  * the number of VOPs and the position of the second VOP */
33 static void scan_buffer(const uint8_t *buf, int buf_size,
34  int *pos_p, int *nb_vop, int *pos_vop2) {
35  uint32_t startcode;
36  const uint8_t *end = buf + buf_size, *pos = buf;
37 
38  while (pos < end) {
39  startcode = -1;
40  pos = avpriv_find_start_code(pos, end, &startcode);
41 
42  if (startcode == USER_DATA_STARTCODE && pos_p) {
43  /* check if the (DivX) userdata string ends with 'p' (packed) */
44  for (int i = 0; i < 255 && pos + i + 1 < end; i++) {
45  if (pos[i] == 'p' && pos[i + 1] == '\0') {
46  *pos_p = pos + i - buf;
47  break;
48  }
49  }
50  } else if (startcode == VOP_STARTCODE && nb_vop) {
51  *nb_vop += 1;
52  if (*nb_vop == 2 && pos_vop2) {
53  *pos_vop2 = pos - buf - 4; /* subtract 4 bytes startcode */
54  }
55  }
56  }
57 }
58 
60 {
62  int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;
63 
64  ret = ff_bsf_get_packet_ref(ctx, pkt);
65  if (ret < 0)
66  return ret;
67 
68  scan_buffer(pkt->data, pkt->size, &pos_p, &nb_vop, &pos_vop2);
69  av_log(ctx, AV_LOG_DEBUG, "Found %d VOP startcode(s) in this packet.\n", nb_vop);
70 
71  if (pos_vop2 >= 0) {
72  if (s->b_frame_ref) {
74  "Missing one N-VOP packet, discarding one B-frame.\n");
76  }
77  /* store a reference to the packed B-frame's data in the BSFContext */
78  s->b_frame_ref = av_buffer_ref(pkt->buf);
79  if (!s->b_frame_ref) {
80  ret = AVERROR(ENOMEM);
81  goto fail;
82  }
83  s->b_frame_ref->data = pkt->data + pos_vop2;
84  s->b_frame_ref->size = pkt->size - pos_vop2;
85  }
86 
87  if (nb_vop > 2) {
89  "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);
90  }
91 
92  if (nb_vop == 1 && s->b_frame_ref) {
93  AVBufferRef *tmp = pkt->buf;
94 
95  /* make tmp accurately reflect the packet's data */
96  tmp->data = pkt->data;
97  tmp->size = pkt->size;
98 
99  /* replace data in packet with stored data */
100  pkt->buf = s->b_frame_ref;
101  pkt->data = s->b_frame_ref->data;
102  pkt->size = s->b_frame_ref->size;
103 
104  /* store reference to data into BSFContext */
105  s->b_frame_ref = tmp;
106 
107  if (s->b_frame_ref->size <= MAX_NVOP_SIZE) {
108  /* N-VOP - discard stored data */
109  av_log(ctx, AV_LOG_DEBUG, "Skipping N-VOP.\n");
111  }
112  } else if (nb_vop >= 2) {
113  /* use first frame of the packet */
114  pkt->size = pos_vop2;
115  } else if (pos_p >= 0) {
117  if (ret < 0)
118  goto fail;
119  av_log(ctx, AV_LOG_DEBUG, "Updating DivX userdata (remove trailing 'p').\n");
120  /* remove 'p' (packed) from the end of the (DivX) userdata string */
121  pkt->data[pos_p] = '\0';
122  } else {
123  /* use packet as is */
124  }
125 
126 fail:
127  if (ret < 0)
128  av_packet_unref(pkt);
129 
130  return ret;
131 }
132 
134 {
135  if (ctx->par_in->extradata) {
136  int pos_p_ext = -1;
137  scan_buffer(ctx->par_in->extradata, ctx->par_in->extradata_size, &pos_p_ext, NULL, NULL);
138  if (pos_p_ext >= 0) {
139  av_log(ctx, AV_LOG_DEBUG,
140  "Updating DivX userdata (remove trailing 'p') in extradata.\n");
141  ctx->par_out->extradata[pos_p_ext] = '\0';
142  }
143  }
144 
145  return 0;
146 }
147 
149 {
152 }
153 
154 static const enum AVCodecID codec_ids[] = {
156 };
157 
159  .name = "mpeg4_unpack_bframes",
160  .priv_data_size = sizeof(UnpackBFramesBSFContext),
165  .codec_ids = codec_ids,
166 };
#define NULL
Definition: coverity.c:32
AVCodecParameters * par_out
Parameters of the output stream.
Definition: avcodec.h:5808
void av_buffer_unref(AVBufferRef **buf)
Free a given reference and automatically free the buffer if there are no more references to it...
Definition: buffer.c:125
static void flush(AVCodecContext *avctx)
#define AV_LOG_WARNING
Something somehow does not look correct.
Definition: log.h:182
static av_cold int init(AVCodecContext *avctx)
Definition: avrndec.c:35
The bitstream filter state.
Definition: avcodec.h:5774
int size
Definition: avcodec.h:1481
static AVPacket pkt
void * priv_data
Opaque filter-specific private data.
Definition: avcodec.h:5795
#define USER_DATA_STARTCODE
Definition: mpeg4video.h:62
uint8_t
const AVBitStreamFilter ff_mpeg4_unpack_bframes_bsf
#define VOP_STARTCODE
Definition: mpeg4video.h:65
static av_cold int end(AVCodecContext *avctx)
Definition: avrndec.c:90
static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *pkt)
const char * name
Definition: avcodec.h:5824
uint8_t * data
Definition: avcodec.h:1480
#define av_log(a,...)
const uint8_t * avpriv_find_start_code(const uint8_t *p, const uint8_t *end, uint32_t *state)
int av_packet_make_writable(AVPacket *pkt)
Create a writable reference for the data described by a given packet, avoiding data copy if possible...
Definition: avpacket.c:682
#define i(width, name, range_min, range_max)
Definition: cbs_h2645.c:259
AVCodecID
Identify the syntax and semantics of the bitstream.
Definition: avcodec.h:215
filter_frame For filters that do not use the this method is called when a frame is pushed to the filter s input It can be called at any time except in a reentrant way If the input frame is enough to produce then the filter should push the output frames on the output link immediately As an exception to the previous rule if the input frame is enough to produce several output frames then the filter needs output only at least one per link The additional frames can be left buffered in the filter
#define AV_LOG_DEBUG
Stuff which is only useful for libav* developers.
Definition: log.h:197
AVBufferRef * buf
A reference to the reference-counted buffer where the packet data is stored.
Definition: avcodec.h:1463
#define fail()
Definition: checkasm.h:122
int extradata_size
Size of the extradata content in bytes.
Definition: avcodec.h:3986
static void mpeg4_unpack_bframes_close_flush(AVBSFContext *bsfc)
AVFormatContext * ctx
Definition: movenc.c:48
static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)
#define s(width, name)
Definition: cbs_vp9.c:257
Libavcodec external API header.
void av_packet_unref(AVPacket *pkt)
Wipe the packet.
Definition: avpacket.c:599
uint8_t * data
The data buffer.
Definition: buffer.h:89
void * buf
Definition: avisynth_c.h:766
static void scan_buffer(const uint8_t *buf, int buf_size, int *pos_p, int *nb_vop, int *pos_vop2)
int size
Size of data in bytes.
Definition: buffer.h:93
static enum AVCodecID codec_ids[]
A reference to a data buffer.
Definition: buffer.h:81
common internal api header.
AVBufferRef * av_buffer_ref(AVBufferRef *buf)
Create a new reference to an AVBuffer.
Definition: buffer.c:93
uint8_t * extradata
Extra binary data needed for initializing the decoder, codec-dependent.
Definition: avcodec.h:3982
Filter the word “frame” indicates either a video frame or a group of audio as stored in an AVFrame structure Format for each input and each output the list of supported formats For video that means pixel format For audio that means channel sample they are references to shared objects When the negotiation mechanism computes the intersection of the formats supported at each end of a all references to both lists are replaced with a reference to the intersection And when a single format is eventually chosen for a link amongst the remaining all references to the list are updated That means that if a filter requires that its input and output have the same format amongst a supported all it has to do is use a reference to the same list of formats query_formats can leave some formats unset and return AVERROR(EAGAIN) to cause the negotiation mechanism toagain later.That can be used by filters with complex requirements to use the format negotiated on one link to set the formats supported on another.Frame references ownership and permissions
This structure stores compressed data.
Definition: avcodec.h:1457
AVCodecParameters * par_in
Parameters of the input stream.
Definition: avcodec.h:5802
int ff_bsf_get_packet_ref(AVBSFContext *ctx, AVPacket *pkt)
Called by bitstream filters to get packet for filtering.
Definition: bsf.c:239
#define MAX_NVOP_SIZE
Definition: mpeg4video.h:72
static uint8_t tmp[11]
Definition: aes_ctr.c:26