mirror of https://git.ffmpeg.org/ffmpeg.git
mp3enc: mux a XING header
The patch below provides exactly that to the MP3 muxer. A XING header containing * the numer of frames, * the size, and * a TOC is generated. It's based on an idea by Anton Khirnov (restricted to the number of frames) found at http://patches.ffmpeg.org/patch/1891/ The TOC is generated as found in lame's "VbrTag.c". According to my tests the following reproduces the number of frames, the size and the TOC in "c.mp3" from "b.mp3" (except a shift due to shorter XING header generated by FFmpeg): lame -V2 a.wav b.mp3 ffmpeg -i b.mp3 -acodec copy -y c.mp3
This commit is contained in:
Peter Belkner
Michael Niedermayer
parent
c34cb130b6
commit
d62bf5d4e7
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@ -27,6 +27,9 @@
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#include "libavutil/avstring.h"
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#include "libavutil/intreadwrite.h"
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#include "libavutil/opt.h"
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#include "libavcodec/mpegaudiodata.h"
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#include "libavcodec/mpegaudiodecheader.h"
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#include "libavformat/avio_internal.h"
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static int id3v1_set_string(AVFormatContext *s, const char *key,
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uint8_t *buf, int buf_size)
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@ -127,7 +130,7 @@ static int id3v2_put_ttag(AVFormatContext *s, const char *str1, const char *str2
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return len + ID3v2_HEADER_SIZE;
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}
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static int mp3_write_trailer(struct AVFormatContext *s)
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static int mp2_write_trailer(struct AVFormatContext *s)
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{
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uint8_t buf[ID3v1_TAG_SIZE];
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@ -150,14 +153,29 @@ AVOutputFormat ff_mp2_muxer = {
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CODEC_ID_NONE,
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NULL,
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ff_raw_write_packet,
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mp3_write_trailer,
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mp2_write_trailer,
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};
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#endif
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#if CONFIG_MP3_MUXER
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#define VBR_NUM_BAGS 400
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#define VBR_TOC_SIZE 100
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typedef struct MP3Context {
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const AVClass *class;
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int id3v2_version;
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struct xing_header {
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int64_t offset;
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int32_t frames;
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int32_t size;
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/* following lame's "VbrTag.c". */
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struct xing_toc {
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uint32_t want;
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uint32_t seen;
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uint32_t pos;
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uint64_t sum;
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uint64_t bag[VBR_NUM_BAGS];
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} toc;
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} xing_header;
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} MP3Context;
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static const AVOption options[] = {
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@ -188,6 +206,156 @@ static int id3v2_check_write_tag(AVFormatContext *s, AVMetadataTag *t, const cha
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return -1;
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}
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static const int64_t xing_offtbl[2][2] = {{32, 17}, {17,9}};
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static const uint32_t XING = MKBETAG('X', 'i', 'n', 'g');
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#ifdef FILTER_VBR_HEADERS
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static const uint32_t INFO = MKBETAG('I', 'n', 'f', 'o');
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static const uint32_t VBRI = MKBETAG('V', 'B', 'R', 'I');
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#endif
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/*
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* Write an empty XING header and initialize respective data.
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*/
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static int mp3_write_xing(AVFormatContext *s)
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{
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AVCodecContext *codec = s->streams[0]->codec;
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MP3Context *mp3 = s->priv_data;
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int bitrate_idx = 3;
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int64_t xing_offset;
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int32_t mask, header;
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MPADecodeHeader c;
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int srate_idx, i, channels;
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int needed;
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for (i = 0; i < FF_ARRAY_ELEMS(ff_mpa_freq_tab); i++)
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if (ff_mpa_freq_tab[i] == codec->sample_rate) {
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srate_idx = i;
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break;
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}
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if (i == FF_ARRAY_ELEMS(ff_mpa_freq_tab)) {
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av_log(s, AV_LOG_ERROR, "Unsupported sample rate.\n");
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return -1;
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}
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switch (codec->channels) {
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case 1: channels = MPA_MONO; break;
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case 2: channels = MPA_STEREO; break;
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default: av_log(s, AV_LOG_ERROR, "Unsupported number of channels.\n"); return -1;
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}
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/* dummy MPEG audio header */
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header = 0xff << 24; // sync
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header |= (0x7 << 5 | 0x3 << 3 | 0x1 << 1 | 0x1) << 16; // sync/mpeg-1/layer 3/no crc*/
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header |= (srate_idx << 2) << 8;
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header |= channels << 6;
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for (;;) {
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if (15 == bitrate_idx)
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return -1;
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mask = (bitrate_idx << 4) << 8;
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header |= mask;
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ff_mpegaudio_decode_header(&c, header);
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xing_offset=xing_offtbl[c.lsf == 1][c.nb_channels == 1];
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needed = 4 // header
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+ xing_offset
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+ 4 // xing tag
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+ 4 // frames/size/toc flags
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+ 4 // frames
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+ 4 // size
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+ VBR_TOC_SIZE; // toc
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if (needed <= c.frame_size)
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break;
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header &= ~mask;
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++bitrate_idx;
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}
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avio_wb32(s->pb, header);
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ffio_fill(s->pb, 0, xing_offset);
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avio_wb32(s->pb, XING);
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avio_wb32(s->pb, 0x01 | 0x02 | 0x04); // frames/size/toc
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mp3->xing_header.offset = avio_tell(s->pb);
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mp3->xing_header.size = c.frame_size;
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mp3->xing_header.toc.want=1;
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mp3->xing_header.toc.seen=0;
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mp3->xing_header.toc.pos=0;
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mp3->xing_header.toc.sum=0;
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avio_wb32(s->pb, 0); // frames
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avio_wb32(s->pb, 0); // size
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// toc
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for (i = 0; i < VBR_TOC_SIZE; ++i)
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avio_w8(s->pb, (uint8_t)(255 * i / VBR_TOC_SIZE));
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ffio_fill(s->pb, 0, c.frame_size - needed);
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avio_flush(s->pb);
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return 0;
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}
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/*
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* Add a frame to XING data.
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* Following lame's "VbrTag.c".
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*/
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static void mp3_xing_add_frame(AVFormatContext *s, AVPacket *pkt, MPADecodeHeader *c)
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{
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MP3Context *mp3 = s->priv_data;
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struct xing_header *xing_header = &mp3->xing_header;
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struct xing_toc *toc = &xing_header->toc;
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int i;
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++xing_header->frames;
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xing_header->size += pkt->size;
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toc->sum += c->bit_rate / 1000;
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if (toc->want == ++toc->seen) {
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toc->bag[toc->pos] = toc->sum;
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if (VBR_NUM_BAGS == ++toc->pos) {
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/* shrink table to half size by throwing away each second bag. */
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for (i = 1; i < VBR_NUM_BAGS; i += 2)
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toc->bag[i >> 1] = toc->bag[i];
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/* double wanted amount per bag. */
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toc->want <<= 1;
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/* adjust current position to half of table size. */
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toc->pos >>= 1;
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}
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toc->seen = 0;
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}
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}
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static void mp3_fix_xing(AVFormatContext *s)
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{
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MP3Context *mp3 = s->priv_data;
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struct xing_header *xing_header = &mp3->xing_header;
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struct xing_toc *toc = &xing_header->toc;
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double scale = (double)toc->pos / (double)VBR_TOC_SIZE;
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int i;
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avio_flush(s->pb);
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avio_seek(s->pb, xing_header->offset, SEEK_SET);
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avio_wb32(s->pb, xing_header->frames);
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avio_wb32(s->pb, xing_header->size);
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avio_w8(s->pb, 0); // first toc entry has to be zero.
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for (i = 1; i < VBR_TOC_SIZE; ++i) {
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int j = (int)floor(scale * i);
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int seek_point = (int)floor(256.0 * toc->bag[j] / toc->sum);
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avio_w8(s->pb, (uint8_t)(seek_point < 256 ? seek_point : 255));
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}
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avio_flush(s->pb);
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avio_seek(s->pb, 0, SEEK_END);
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}
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/**
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* Write an ID3v2 header at beginning of stream
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*/
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@ -236,6 +404,61 @@ static int mp3_write_header(struct AVFormatContext *s)
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id3v2_put_size(s, totlen);
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avio_seek(s->pb, cur_pos, SEEK_SET);
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if (s->pb->seekable)
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mp3_write_xing(s);
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return 0;
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}
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static int mp3_write_packet(AVFormatContext *s, AVPacket *pkt)
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{
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if (! pkt || ! pkt->data || pkt->size < 4)
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return ff_raw_write_packet(s, pkt);
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else {
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MP3Context *mp3 = s->priv_data;
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MPADecodeHeader c;
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#ifdef FILTER_VBR_HEADERS
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int base;
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#endif
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ff_mpegaudio_decode_header(&c, AV_RB32(pkt->data));
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#ifdef FILTER_VBR_HEADERS
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/* filter out XING and INFO headers. */
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base = 4 + xing_offtbl[c.lsf == 1][c.nb_channels == 1];
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if (base + 4 <= pkt->size) {
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uint32_t v = AV_RB32(pkt->data + base);
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if (XING == v || INFO == v)
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return 0;
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}
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/* filter out VBRI headers. */
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base = 4 + 32;
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if (base + 4 <= pkt->size && VBRI == AV_RB32(pkt->data + base))
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return 0;
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#endif
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if (0 < mp3->xing_header.offset)
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mp3_xing_add_frame(s, pkt, &c);
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return ff_raw_write_packet(s, pkt);
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}
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}
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static int mp3_write_trailer(AVFormatContext *s)
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{
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MP3Context *mp3 = s->priv_data;
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int ret=mp2_write_trailer(s);
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if (ret < 0)
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return ret;
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if (0 < mp3->xing_header.offset)
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mp3_fix_xing(s);
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return 0;
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}
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@ -248,7 +471,7 @@ AVOutputFormat ff_mp3_muxer = {
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CODEC_ID_MP3,
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CODEC_ID_NONE,
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mp3_write_header,
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ff_raw_write_packet,
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mp3_write_packet,
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mp3_write_trailer,
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AVFMT_NOTIMESTAMPS,
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.priv_class = &mp3_muxer_class,
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