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libavcodec/mpegaudio_parser.c

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00001 /*
00002  * MPEG Audio parser
00003  * Copyright (c) 2003 Fabrice Bellard
00004  * Copyright (c) 2003 Michael Niedermayer
00005  *
00006  * This file is part of FFmpeg.
00007  *
00008  * FFmpeg is free software; you can redistribute it and/or
00009  * modify it under the terms of the GNU Lesser General Public
00010  * License as published by the Free Software Foundation; either
00011  * version 2.1 of the License, or (at your option) any later version.
00012  *
00013  * FFmpeg is distributed in the hope that it will be useful,
00014  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00015  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00016  * Lesser General Public License for more details.
00017  *
00018  * You should have received a copy of the GNU Lesser General Public
00019  * License along with FFmpeg; if not, write to the Free Software
00020  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00021  */
00022 
00023 #include "parser.h"
00024 #include "mpegaudio.h"
00025 #include "mpegaudiodecheader.h"
00026 
00027 
00028 typedef struct MpegAudioParseContext {
00029     uint8_t inbuf[MPA_MAX_CODED_FRAME_SIZE];    /* input buffer */
00030     uint8_t *inbuf_ptr;
00031     int frame_size;
00032     int free_format_frame_size;
00033     int free_format_next_header;
00034     uint32_t header;
00035     int header_count;
00036 } MpegAudioParseContext;
00037 
00038 #define MPA_HEADER_SIZE 4
00039 
00040 /* header + layer + bitrate + freq + lsf/mpeg25 */
00041 #undef SAME_HEADER_MASK /* mpegaudio.h defines different version */
00042 #define SAME_HEADER_MASK \
00043    (0xffe00000 | (3 << 17) | (3 << 10) | (3 << 19))
00044 
00045 /* useful helper to get mpeg audio stream infos. Return -1 if error in
00046    header, otherwise the coded frame size in bytes */
00047 int ff_mpa_decode_header(AVCodecContext *avctx, uint32_t head, int *sample_rate, int *channels, int *frame_size, int *bit_rate)
00048 {
00049     MPADecodeHeader s1, *s = &s1;
00050 
00051     if (ff_mpa_check_header(head) != 0)
00052         return -1;
00053 
00054     if (ff_mpegaudio_decode_header(s, head) != 0) {
00055         return -1;
00056     }
00057 
00058     switch(s->layer) {
00059     case 1:
00060         avctx->codec_id = CODEC_ID_MP1;
00061         *frame_size = 384;
00062         break;
00063     case 2:
00064         avctx->codec_id = CODEC_ID_MP2;
00065         *frame_size = 1152;
00066         break;
00067     default:
00068     case 3:
00069         avctx->codec_id = CODEC_ID_MP3;
00070         if (s->lsf)
00071             *frame_size = 576;
00072         else
00073             *frame_size = 1152;
00074         break;
00075     }
00076 
00077     *sample_rate = s->sample_rate;
00078     *channels = s->nb_channels;
00079     *bit_rate = s->bit_rate;
00080     avctx->sub_id = s->layer;
00081     return s->frame_size;
00082 }
00083 
00084 static av_cold int mpegaudio_parse_init(AVCodecParserContext *s1)
00085 {
00086     MpegAudioParseContext *s = s1->priv_data;
00087     s->inbuf_ptr = s->inbuf;
00088     return 0;
00089 }
00090 
00091 static int mpegaudio_parse(AVCodecParserContext *s1,
00092                            AVCodecContext *avctx,
00093                            const uint8_t **poutbuf, int *poutbuf_size,
00094                            const uint8_t *buf, int buf_size)
00095 {
00096     MpegAudioParseContext *s = s1->priv_data;
00097     int len, ret, sr, channels, bit_rate, frame_size;
00098     uint32_t header;
00099     const uint8_t *buf_ptr;
00100 
00101     *poutbuf = NULL;
00102     *poutbuf_size = 0;
00103     buf_ptr = buf;
00104     while (buf_size > 0) {
00105         len = s->inbuf_ptr - s->inbuf;
00106         if (s->frame_size == 0) {
00107             /* special case for next header for first frame in free
00108                format case (XXX: find a simpler method) */
00109             if (s->free_format_next_header != 0) {
00110                 AV_WB32(s->inbuf, s->free_format_next_header);
00111                 s->inbuf_ptr = s->inbuf + 4;
00112                 s->free_format_next_header = 0;
00113                 goto got_header;
00114             }
00115             /* no header seen : find one. We need at least MPA_HEADER_SIZE
00116                bytes to parse it */
00117             len = FFMIN(MPA_HEADER_SIZE - len, buf_size);
00118             if (len > 0) {
00119                 memcpy(s->inbuf_ptr, buf_ptr, len);
00120                 buf_ptr += len;
00121                 buf_size -= len;
00122                 s->inbuf_ptr += len;
00123             }
00124             if ((s->inbuf_ptr - s->inbuf) >= MPA_HEADER_SIZE) {
00125             got_header:
00126                 header = AV_RB32(s->inbuf);
00127 
00128                 ret = ff_mpa_decode_header(avctx, header, &sr, &channels, &frame_size, &bit_rate);
00129                 if (ret < 0) {
00130                     s->header_count= -2;
00131                     /* no sync found : move by one byte (inefficient, but simple!) */
00132                     memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
00133                     s->inbuf_ptr--;
00134                     dprintf(avctx, "skip %x\n", header);
00135                     /* reset free format frame size to give a chance
00136                        to get a new bitrate */
00137                     s->free_format_frame_size = 0;
00138                 } else {
00139                     if((header&SAME_HEADER_MASK) != (s->header&SAME_HEADER_MASK) && s->header)
00140                         s->header_count= -3;
00141                     s->header= header;
00142                     s->header_count++;
00143                     s->frame_size = ret;
00144 
00145 #if 0
00146                     /* free format: prepare to compute frame size */
00147                     if (ff_mpegaudio_decode_header((MPADecodeHeader *)s, header) == 1) {
00148                         s->frame_size = -1;
00149                     }
00150 #endif
00151                     if(s->header_count > 1){
00152                         avctx->sample_rate= sr;
00153                         avctx->channels   = channels;
00154                         avctx->frame_size = frame_size;
00155                         avctx->bit_rate   = bit_rate;
00156                     }
00157                 }
00158             }
00159         } else
00160 #if 0
00161         if (s->frame_size == -1) {
00162             /* free format : find next sync to compute frame size */
00163             len = MPA_MAX_CODED_FRAME_SIZE - len;
00164             if (len > buf_size)
00165                 len = buf_size;
00166             if (len == 0) {
00167                 /* frame too long: resync */
00168                 s->frame_size = 0;
00169                 memmove(s->inbuf, s->inbuf + 1, s->inbuf_ptr - s->inbuf - 1);
00170                 s->inbuf_ptr--;
00171             } else {
00172                 uint8_t *p, *pend;
00173                 uint32_t header1;
00174                 int padding;
00175 
00176                 memcpy(s->inbuf_ptr, buf_ptr, len);
00177                 /* check for header */
00178                 p = s->inbuf_ptr - 3;
00179                 pend = s->inbuf_ptr + len - 4;
00180                 while (p <= pend) {
00181                     header = AV_RB32(p);
00182                     header1 = AV_RB32(s->inbuf);
00183                     /* check with high probability that we have a
00184                        valid header */
00185                     if ((header & SAME_HEADER_MASK) ==
00186                         (header1 & SAME_HEADER_MASK)) {
00187                         /* header found: update pointers */
00188                         len = (p + 4) - s->inbuf_ptr;
00189                         buf_ptr += len;
00190                         buf_size -= len;
00191                         s->inbuf_ptr = p;
00192                         /* compute frame size */
00193                         s->free_format_next_header = header;
00194                         s->free_format_frame_size = s->inbuf_ptr - s->inbuf;
00195                         padding = (header1 >> 9) & 1;
00196                         if (s->layer == 1)
00197                             s->free_format_frame_size -= padding * 4;
00198                         else
00199                             s->free_format_frame_size -= padding;
00200                         dprintf(avctx, "free frame size=%d padding=%d\n",
00201                                 s->free_format_frame_size, padding);
00202                         ff_mpegaudio_decode_header((MPADecodeHeader *)s, header1);
00203                         goto next_data;
00204                     }
00205                     p++;
00206                 }
00207                 /* not found: simply increase pointers */
00208                 buf_ptr += len;
00209                 s->inbuf_ptr += len;
00210                 buf_size -= len;
00211             }
00212         } else
00213 #endif
00214         if (len < s->frame_size) {
00215             if (s->frame_size > MPA_MAX_CODED_FRAME_SIZE)
00216                 s->frame_size = MPA_MAX_CODED_FRAME_SIZE;
00217             len = FFMIN(s->frame_size - len, buf_size);
00218             memcpy(s->inbuf_ptr, buf_ptr, len);
00219             buf_ptr += len;
00220             s->inbuf_ptr += len;
00221             buf_size -= len;
00222         }
00223 
00224         if(s->frame_size > 0 && buf_ptr - buf == s->inbuf_ptr - s->inbuf
00225            && buf_size + buf_ptr - buf >= s->frame_size){
00226             if(s->header_count > 0){
00227                 *poutbuf = buf;
00228                 *poutbuf_size = s->frame_size;
00229             }
00230             buf_ptr = buf + s->frame_size;
00231             s->inbuf_ptr = s->inbuf;
00232             s->frame_size = 0;
00233             break;
00234         }
00235 
00236         //    next_data:
00237         if (s->frame_size > 0 &&
00238             (s->inbuf_ptr - s->inbuf) >= s->frame_size) {
00239             if(s->header_count > 0){
00240                 *poutbuf = s->inbuf;
00241                 *poutbuf_size = s->inbuf_ptr - s->inbuf;
00242             }
00243             s->inbuf_ptr = s->inbuf;
00244             s->frame_size = 0;
00245             break;
00246         }
00247     }
00248     return buf_ptr - buf;
00249 }
00250 
00251 
00252 AVCodecParser mpegaudio_parser = {
00253     { CODEC_ID_MP1, CODEC_ID_MP2, CODEC_ID_MP3 },
00254     sizeof(MpegAudioParseContext),
00255     mpegaudio_parse_init,
00256     mpegaudio_parse,
00257     NULL,
00258 };

Generated on Tue Nov 4 2014 12:59:22 for ffmpeg by  doxygen 1.7.1