FFmpeg: libavcodec/mpeg4_unpack_bframes_bsf.c Source File

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mpeg4_unpack_bframes_bsf.c

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1 /*

2 * Bitstream filter for unpacking DivX-style packed B-frames in MPEG-4 (divx_packed)

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 */

22 #include "bsf.h"

23 #include "bsf_internal.h"

24 #include "mpeg4videodefs.h"

25 #include "startcode.h"

27 typedef struct UnpackBFramesBSFContext {

28 AVBufferRef *b_frame_ref;

29 } UnpackBFramesBSFContext;

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;

38 while (pos < end) {

39 startcode = -1;

40 pos = avpriv_find_start_code(pos, end, &startcode);

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円') {

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 }

59 static int mpeg4_unpack_bframes_filter(AVBSFContext *ctx, AVPacket *pkt)

60 {

61 UnpackBFramesBSFContext *s = ctx->priv_data;

62 int pos_p = -1, nb_vop = 0, pos_vop2 = -1, ret = 0;

64 ret = ff_bsf_get_packet_ref(ctx, pkt);

65 if (ret < 0)

66 return ret;

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);

71 if (pos_vop2 >= 0) {

72 if (s->b_frame_ref) {

73 av_log(ctx, AV_LOG_WARNING,

74 "Missing one N-VOP packet, discarding one B-frame.\n");

75 av_buffer_unref(&s->b_frame_ref);

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 }

87 if (nb_vop > 2) {

88 av_log(ctx, AV_LOG_WARNING,

89 "Found %d VOP headers in one packet, only unpacking one.\n", nb_vop);

90 }

92 if (nb_vop == 1 && s->b_frame_ref) {

93 AVBufferRef *tmp = pkt->buf;

95 /* make tmp accurately reflect the packet's data */

96 tmp->data = pkt->data;

97 tmp->size = pkt->size;

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");

110 av_buffer_unref(&s->b_frame_ref);

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) {

116 ret = av_packet_make_writable(pkt);

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円';

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

133 static int mpeg4_unpack_bframes_init(AVBSFContext *ctx)

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円';

142 }

143 }

144

145 return 0;

146 }

147

148 static void mpeg4_unpack_bframes_close_flush(AVBSFContext *bsfc)

149 {

150 UnpackBFramesBSFContext *ctx = bsfc->priv_data;

151 av_buffer_unref(&ctx->b_frame_ref);

152 }

153

154 static const enum AVCodecID codec_ids[] = {

155 AV_CODEC_ID_MPEG4, AV_CODEC_ID_NONE,

156 };

157

158 const FFBitStreamFilter ff_mpeg4_unpack_bframes_bsf = {

159 .p.name = "mpeg4_unpack_bframes",

160 .p.codec_ids = codec_ids,

161 .priv_data_size = sizeof(UnpackBFramesBSFContext),

162 .init = mpeg4_unpack_bframes_init,

163 .filter = mpeg4_unpack_bframes_filter,

164 .flush = mpeg4_unpack_bframes_close_flush,

165 .close = mpeg4_unpack_bframes_close_flush,

166 };

av_packet_unref

void av_packet_unref(AVPacket *pkt)

Wipe the packet.

Definition: avpacket.c:422

AV_LOG_WARNING

#define AV_LOG_WARNING

Something somehow does not look correct.

Definition: log.h:186

AVERROR

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

bsf_internal.h

AVBitStreamFilter::name

const char * name

Definition: bsf.h:112

AV_CODEC_ID_MPEG4

@ AV_CODEC_ID_MPEG4

Definition: codec_id.h:64

tmp

static uint8_t tmp[11]

Definition: aes_ctr.c:28

AVPacket::data

uint8_t * data

Definition: packet.h:374

filter

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

Definition: filter_design.txt:228

av_buffer_ref

AVBufferRef * av_buffer_ref(const AVBufferRef *buf)

Create a new reference to an AVBuffer.

Definition: buffer.c:103

AVBSFContext

The bitstream filter state.

Definition: bsf.h:68

UnpackBFramesBSFContext

Definition: mpeg4_unpack_bframes_bsf.c:27

bsf.h

fail