Libav 0.7.1
libavcodec/flac_parser.c
Go to the documentation of this file.
00001 /*
00002  * FLAC parser
00003  * Copyright (c) 2010 Michael Chinen
00004  *
00005  * This file is part of Libav.
00006  *
00007  * Libav is free software; you can redistribute it and/or
00008  * modify it under the terms of the GNU Lesser General Public
00009  * License as published by the Free Software Foundation; either
00010  * version 2.1 of the License, or (at your option) any later version.
00011  *
00012  * Libav is distributed in the hope that it will be useful,
00013  * but WITHOUT ANY WARRANTY; without even the implied warranty of
00014  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
00015  * Lesser General Public License for more details.
00016  *
00017  * You should have received a copy of the GNU Lesser General Public
00018  * License along with Libav; if not, write to the Free Software
00019  * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
00020  */
00021 
00035 #include "libavutil/crc.h"
00036 #include "libavutil/fifo.h"
00037 #include "bytestream.h"
00038 #include "parser.h"
00039 #include "flac.h"
00040 
00042 #define FLAC_MAX_SEQUENTIAL_HEADERS 3
00043 
00044 #define FLAC_MIN_HEADERS 10
00045 
00046 #define FLAC_AVG_FRAME_SIZE 8192
00047 
00049 #define FLAC_HEADER_BASE_SCORE        10
00050 #define FLAC_HEADER_CHANGED_PENALTY   7
00051 #define FLAC_HEADER_CRC_FAIL_PENALTY  50
00052 #define FLAC_HEADER_NOT_PENALIZED_YET 100000
00053 #define FLAC_HEADER_NOT_SCORED_YET    -100000
00054 
00056 #define MAX_FRAME_HEADER_SIZE 16
00057 
00058 typedef struct FLACHeaderMarker {
00059     int offset;       
00060     int *link_penalty;  
00062     int max_score;    
00064     FLACFrameInfo fi; 
00065     struct FLACHeaderMarker *next;       
00068     struct FLACHeaderMarker *best_child; 
00071 } FLACHeaderMarker;
00072 
00073 typedef struct FLACParseContext {
00074     AVCodecContext *avctx;         
00075     FLACHeaderMarker *headers;     
00077     FLACHeaderMarker *best_header; 
00078     int nb_headers_found;          
00080     int nb_headers_buffered;       
00081     int best_header_valid;         
00083     AVFifoBuffer *fifo_buf;        
00085     int end_padded;                
00086     uint8_t *wrap_buf;             
00087     int wrap_buf_allocated_size;   
00088 } FLACParseContext;
00089 
00090 static int frame_header_is_valid(AVCodecContext *avctx, const uint8_t *buf,
00091                                  FLACFrameInfo *fi)
00092 {
00093     GetBitContext gb;
00094     init_get_bits(&gb, buf, MAX_FRAME_HEADER_SIZE * 8);
00095     return !ff_flac_decode_frame_header(avctx, &gb, fi, 127);
00096 }
00097 
00111 static uint8_t* flac_fifo_read_wrap(FLACParseContext *fpc, int offset, int len,
00112                                uint8_t** wrap_buf, int* allocated_size)
00113 {
00114     AVFifoBuffer *f   = fpc->fifo_buf;
00115     uint8_t *start    = f->rptr + offset;
00116     uint8_t *tmp_buf;
00117 
00118     if (start >= f->end)
00119         start -= f->end - f->buffer;
00120     if (f->end - start >= len)
00121         return start;
00122 
00123     tmp_buf = av_fast_realloc(*wrap_buf, allocated_size, len);
00124 
00125     if (!tmp_buf) {
00126         av_log(fpc->avctx, AV_LOG_ERROR,
00127                "couldn't reallocate wrap buffer of size %d", len);
00128         return NULL;
00129     }
00130     *wrap_buf = tmp_buf;
00131     do {
00132         int seg_len = FFMIN(f->end - start, len);
00133         memcpy(tmp_buf, start, seg_len);
00134         tmp_buf = (uint8_t*)tmp_buf + seg_len;
00135 // memory barrier needed for SMP here in theory
00136 
00137         start += seg_len - (f->end - f->buffer);
00138         len -= seg_len;
00139     } while (len > 0);
00140 
00141     return *wrap_buf;
00142 }
00143 
00151 static uint8_t* flac_fifo_read(FLACParseContext *fpc, int offset, int *len)
00152 {
00153     AVFifoBuffer *f   = fpc->fifo_buf;
00154     uint8_t *start    = f->rptr + offset;
00155 
00156     if (start >= f->end)
00157         start -= f->end - f->buffer;
00158     *len = FFMIN(*len, f->end - start);
00159     return start;
00160 }
00161 
00162 static int find_headers_search_validate(FLACParseContext *fpc, int offset)
00163 {
00164     FLACFrameInfo fi;
00165     uint8_t *header_buf;
00166     int size = 0;
00167     header_buf = flac_fifo_read_wrap(fpc, offset,
00168                                      MAX_FRAME_HEADER_SIZE,
00169                                      &fpc->wrap_buf,
00170                                      &fpc->wrap_buf_allocated_size);
00171     if (frame_header_is_valid(fpc->avctx, header_buf, &fi)) {
00172         FLACHeaderMarker **end_handle = &fpc->headers;
00173         int i;
00174 
00175         size = 0;
00176         while (*end_handle) {
00177             end_handle = &(*end_handle)->next;
00178             size++;
00179         }
00180 
00181         *end_handle = av_mallocz(sizeof(FLACHeaderMarker));
00182         if (!*end_handle) {
00183             av_log(fpc->avctx, AV_LOG_ERROR,
00184                    "couldn't allocate FLACHeaderMarker\n");
00185             return AVERROR(ENOMEM);
00186         }
00187         (*end_handle)->fi           = fi;
00188         (*end_handle)->offset       = offset;
00189         (*end_handle)->link_penalty = av_malloc(sizeof(int) *
00190                                             FLAC_MAX_SEQUENTIAL_HEADERS);
00191         for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++)
00192             (*end_handle)->link_penalty[i] = FLAC_HEADER_NOT_PENALIZED_YET;
00193 
00194         fpc->nb_headers_found++;
00195         size++;
00196     }
00197     return size;
00198 }
00199 
00200 static int find_headers_search(FLACParseContext *fpc, uint8_t *buf, int buf_size,
00201                                int search_start)
00202 
00203 {
00204     int size = 0, mod_offset = (buf_size - 1) % 4, i, j;
00205     uint32_t x;
00206 
00207     for (i = 0; i < mod_offset; i++) {
00208         if ((AV_RB16(buf + i) & 0xFFFE) == 0xFFF8)
00209             size = find_headers_search_validate(fpc, search_start + i);
00210     }
00211 
00212     for (; i < buf_size - 1; i += 4) {
00213         x = AV_RB32(buf + i);
00214         if (((x & ~(x + 0x01010101)) & 0x80808080)) {
00215             for (j = 0; j < 4; j++) {
00216                 if ((AV_RB16(buf + i + j) & 0xFFFE) == 0xFFF8)
00217                     size = find_headers_search_validate(fpc, search_start + i + j);
00218             }
00219         }
00220     }
00221     return size;
00222 }
00223 
00224 static int find_new_headers(FLACParseContext *fpc, int search_start)
00225 {
00226     FLACHeaderMarker *end;
00227     int search_end, size = 0, read_len, temp;
00228     uint8_t *buf;
00229     fpc->nb_headers_found = 0;
00230 
00231     /* Search for a new header of at most 16 bytes. */
00232     search_end = av_fifo_size(fpc->fifo_buf) - (MAX_FRAME_HEADER_SIZE - 1);
00233     read_len   = search_end - search_start + 1;
00234     buf        = flac_fifo_read(fpc, search_start, &read_len);
00235     size       = find_headers_search(fpc, buf, read_len, search_start);
00236     search_start += read_len - 1;
00237 
00238     /* If fifo end was hit do the wrap around. */
00239     if (search_start != search_end) {
00240         uint8_t wrap[2];
00241 
00242         wrap[0]  = buf[read_len - 1];
00243         read_len = search_end - search_start + 1;
00244 
00245         /* search_start + 1 is the post-wrap offset in the fifo. */
00246         buf      = flac_fifo_read(fpc, search_start + 1, &read_len);
00247         wrap[1]  = buf[0];
00248 
00249         if ((AV_RB16(wrap) & 0xFFFE) == 0xFFF8) {
00250             temp = find_headers_search_validate(fpc, search_start);
00251             size = FFMAX(size, temp);
00252         }
00253         search_start++;
00254 
00255         /* Continue to do the last half of the wrap. */
00256         temp     = find_headers_search(fpc, buf, read_len, search_start);
00257         size     = FFMAX(size, temp);
00258         search_start += read_len - 1;
00259     }
00260 
00261     /* Return the size even if no new headers were found. */
00262     if (!size && fpc->headers)
00263         for (end = fpc->headers; end; end = end->next)
00264             size++;
00265     return size;
00266 }
00267 
00268 static int check_header_mismatch(FLACParseContext  *fpc,
00269                                  FLACHeaderMarker  *header,
00270                                  FLACHeaderMarker  *child,
00271                                  int                log_level_offset)
00272 {
00273     FLACFrameInfo  *header_fi = &header->fi, *child_fi = &child->fi;
00274     int deduction = 0, deduction_expected = 0, i;
00275     if (child_fi->samplerate != header_fi->samplerate) {
00276         deduction += FLAC_HEADER_CHANGED_PENALTY;
00277         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
00278                "sample rate change detected in adjacent frames\n");
00279     }
00280     if (child_fi->bps != header_fi->bps) {
00281         deduction += FLAC_HEADER_CHANGED_PENALTY;
00282         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
00283                "bits per sample change detected in adjacent frames\n");
00284     }
00285     if (child_fi->is_var_size != header_fi->is_var_size) {
00286         /* Changing blocking strategy not allowed per the spec */
00287         deduction += FLAC_HEADER_BASE_SCORE;
00288         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
00289                    "blocking strategy change detected in adjacent frames\n");
00290     }
00291     if (child_fi->channels != header_fi->channels) {
00292         deduction += FLAC_HEADER_CHANGED_PENALTY;
00293         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
00294                    "number of channels change detected in adjacent frames\n");
00295     }
00296     /* Check sample and frame numbers. */
00297     if ((child_fi->frame_or_sample_num - header_fi->frame_or_sample_num
00298          != header_fi->blocksize) &&
00299         (child_fi->frame_or_sample_num
00300          != header_fi->frame_or_sample_num + 1)) {
00301         FLACHeaderMarker *curr;
00302         int expected_frame_num, expected_sample_num;
00303         /* If there are frames in the middle we expect this deduction,
00304            as they are probably valid and this one follows it */
00305 
00306         expected_frame_num = expected_sample_num = header_fi->frame_or_sample_num;
00307         curr = header;
00308         while (curr != child) {
00309             /* Ignore frames that failed all crc checks */
00310             for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++) {
00311                 if (curr->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY) {
00312                     expected_frame_num++;
00313                     expected_sample_num += curr->fi.blocksize;
00314                     break;
00315                 }
00316             }
00317             curr = curr->next;
00318         }
00319 
00320         if (expected_frame_num  == child_fi->frame_or_sample_num ||
00321             expected_sample_num == child_fi->frame_or_sample_num)
00322             deduction_expected = deduction ? 0 : 1;
00323 
00324         deduction += FLAC_HEADER_CHANGED_PENALTY;
00325         av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
00326                    "sample/frame number mismatch in adjacent frames\n");
00327     }
00328 
00329     /* If we have suspicious headers, check the CRC between them */
00330     if (deduction && !deduction_expected) {
00331         FLACHeaderMarker *curr;
00332         int read_len;
00333         uint8_t *buf;
00334         uint32_t crc = 1;
00335         int inverted_test = 0;
00336 
00337         /* Since CRC is expensive only do it if we haven't yet.
00338            This assumes a CRC penalty is greater than all other check penalties */
00339         curr = header->next;
00340         for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS && curr != child; i++)
00341             curr = curr->next;
00342 
00343         if (header->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY ||
00344             header->link_penalty[i] == FLAC_HEADER_NOT_PENALIZED_YET) {
00345             FLACHeaderMarker *start, *end;
00346 
00347             /* Although overlapping chains are scored, the crc should never
00348                have to be computed twice for a single byte. */
00349             start = header;
00350             end   = child;
00351             if (i > 0 &&
00352                 header->link_penalty[i - 1] >= FLAC_HEADER_CRC_FAIL_PENALTY) {
00353                 while (start->next != child)
00354                     start = start->next;
00355                 inverted_test = 1;
00356             } else if (i > 0 &&
00357                        header->next->link_penalty[i-1] >=
00358                        FLAC_HEADER_CRC_FAIL_PENALTY ) {
00359                 end = header->next;
00360                 inverted_test = 1;
00361             }
00362 
00363             read_len = end->offset - start->offset;
00364             buf      = flac_fifo_read(fpc, start->offset, &read_len);
00365             crc      = av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, buf, read_len);
00366             read_len = (end->offset - start->offset) - read_len;
00367 
00368             if (read_len) {
00369                 buf = flac_fifo_read(fpc, end->offset - read_len, &read_len);
00370                 crc = av_crc(av_crc_get_table(AV_CRC_16_ANSI), crc, buf, read_len);
00371             }
00372         }
00373 
00374         if (!crc ^ !inverted_test) {
00375             deduction += FLAC_HEADER_CRC_FAIL_PENALTY;
00376             av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset,
00377                    "crc check failed from offset %i (frame %"PRId64") to %i (frame %"PRId64")\n",
00378                    header->offset, header_fi->frame_or_sample_num,
00379                    child->offset, child_fi->frame_or_sample_num);
00380         }
00381     }
00382     return deduction;
00383 }
00384 
00395 static int score_header(FLACParseContext *fpc, FLACHeaderMarker *header)
00396 {
00397     FLACHeaderMarker *child;
00398     int dist = 0;
00399     int child_score;
00400 
00401     if (header->max_score != FLAC_HEADER_NOT_SCORED_YET)
00402         return header->max_score;
00403 
00404     header->max_score = FLAC_HEADER_BASE_SCORE;
00405 
00406     /* Check and compute the children's scores. */
00407     child = header->next;
00408     for (dist = 0; dist < FLAC_MAX_SEQUENTIAL_HEADERS && child; dist++) {
00409         /* Look at the child's frame header info and penalize suspicious
00410            changes between the headers. */
00411         if (header->link_penalty[dist] == FLAC_HEADER_NOT_PENALIZED_YET) {
00412             header->link_penalty[dist] = check_header_mismatch(fpc, header,
00413                                                                child, AV_LOG_DEBUG);
00414         }
00415         child_score = score_header(fpc, child) - header->link_penalty[dist];
00416 
00417         if (FLAC_HEADER_BASE_SCORE + child_score > header->max_score) {
00418             /* Keep the child because the frame scoring is dynamic. */
00419             header->best_child = child;
00420             header->max_score  = FLAC_HEADER_BASE_SCORE + child_score;
00421         }
00422         child = child->next;
00423     }
00424 
00425     return header->max_score;
00426 }
00427 
00428 static void score_sequences(FLACParseContext *fpc)
00429 {
00430     FLACHeaderMarker *curr;
00431     int best_score = FLAC_HEADER_NOT_SCORED_YET;
00432     /* First pass to clear all old scores. */
00433     for (curr = fpc->headers; curr; curr = curr->next)
00434         curr->max_score = FLAC_HEADER_NOT_SCORED_YET;
00435 
00436     /* Do a second pass to score them all. */
00437     for (curr = fpc->headers; curr; curr = curr->next) {
00438         if (score_header(fpc, curr) > best_score) {
00439             fpc->best_header = curr;
00440             best_score       = curr->max_score;
00441         }
00442     }
00443 }
00444 
00445 static int get_best_header(FLACParseContext* fpc, const uint8_t **poutbuf,
00446                            int *poutbuf_size)
00447 {
00448     FLACHeaderMarker *header = fpc->best_header;
00449     FLACHeaderMarker *child  = header->best_child;
00450     if (!child) {
00451         *poutbuf_size = av_fifo_size(fpc->fifo_buf) - header->offset;
00452     } else {
00453         *poutbuf_size = child->offset - header->offset;
00454 
00455         /* If the child has suspicious changes, log them */
00456         check_header_mismatch(fpc, header, child, 0);
00457     }
00458 
00459     fpc->avctx->sample_rate = header->fi.samplerate;
00460     fpc->avctx->channels    = header->fi.channels;
00461     fpc->avctx->frame_size  = header->fi.blocksize;
00462     *poutbuf = flac_fifo_read_wrap(fpc, header->offset, *poutbuf_size,
00463                                         &fpc->wrap_buf,
00464                                         &fpc->wrap_buf_allocated_size);
00465 
00466     fpc->best_header_valid = 0;
00467     /* Return the negative overread index so the client can compute pos.
00468        This should be the amount overread to the beginning of the child */
00469     if (child)
00470         return child->offset - av_fifo_size(fpc->fifo_buf);
00471     return 0;
00472 }
00473 
00474 static int flac_parse(AVCodecParserContext *s, AVCodecContext *avctx,
00475                       const uint8_t **poutbuf, int *poutbuf_size,
00476                       const uint8_t *buf, int buf_size)
00477 {
00478     FLACParseContext *fpc = s->priv_data;
00479     FLACHeaderMarker *curr;
00480     int nb_headers;
00481     const uint8_t *read_end   = buf;
00482     const uint8_t *read_start = buf;
00483 
00484     if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) {
00485         FLACFrameInfo fi;
00486         if (frame_header_is_valid(avctx, buf, &fi))
00487             avctx->frame_size = fi.blocksize;
00488         *poutbuf      = buf;
00489         *poutbuf_size = buf_size;
00490         return buf_size;
00491     }
00492 
00493     fpc->avctx = avctx;
00494     if (fpc->best_header_valid)
00495         return get_best_header(fpc, poutbuf, poutbuf_size);
00496 
00497     /* If a best_header was found last call remove it with the buffer data. */
00498     if (fpc->best_header && fpc->best_header->best_child) {
00499         FLACHeaderMarker *temp;
00500         FLACHeaderMarker *best_child = fpc->best_header->best_child;
00501 
00502         /* Remove headers in list until the end of the best_header. */
00503         for (curr = fpc->headers; curr != best_child; curr = temp) {
00504             if (curr != fpc->best_header) {
00505                 av_log(avctx, AV_LOG_DEBUG,
00506                        "dropping low score %i frame header from offset %i to %i\n",
00507                        curr->max_score, curr->offset, curr->next->offset);
00508             }
00509             temp = curr->next;
00510             av_freep(&curr->link_penalty);
00511             av_free(curr);
00512             fpc->nb_headers_buffered--;
00513         }
00514         /* Release returned data from ring buffer. */
00515         av_fifo_drain(fpc->fifo_buf, best_child->offset);
00516 
00517         /* Fix the offset for the headers remaining to match the new buffer. */
00518         for (curr = best_child->next; curr; curr = curr->next)
00519             curr->offset -= best_child->offset;
00520 
00521         fpc->nb_headers_buffered--;
00522         best_child->offset = 0;
00523         fpc->headers       = best_child;
00524         if (fpc->nb_headers_buffered >= FLAC_MIN_HEADERS) {
00525             fpc->best_header = best_child;
00526             return get_best_header(fpc, poutbuf, poutbuf_size);
00527         }
00528         fpc->best_header   = NULL;
00529     } else if (fpc->best_header) {
00530         /* No end frame no need to delete the buffer; probably eof */
00531         FLACHeaderMarker *temp;
00532 
00533         for (curr = fpc->headers; curr != fpc->best_header; curr = temp) {
00534             temp = curr->next;
00535             av_freep(&curr->link_penalty);
00536             av_free(curr);
00537         }
00538         fpc->headers = fpc->best_header->next;
00539         av_freep(&fpc->best_header->link_penalty);
00540         av_freep(&fpc->best_header);
00541     }
00542 
00543     /* Find and score new headers. */
00544     while ((buf && read_end < buf + buf_size &&
00545             fpc->nb_headers_buffered < FLAC_MIN_HEADERS)
00546            || (!buf && !fpc->end_padded)) {
00547         int start_offset;
00548 
00549         /* Pad the end once if EOF, to check the final region for headers. */
00550         if (!buf) {
00551             fpc->end_padded      = 1;
00552             buf_size = MAX_FRAME_HEADER_SIZE;
00553             read_end = read_start + MAX_FRAME_HEADER_SIZE;
00554         } else {
00555             /* The maximum read size is the upper-bound of what the parser
00556                needs to have the required number of frames buffered */
00557             int nb_desired = FLAC_MIN_HEADERS - fpc->nb_headers_buffered + 1;
00558             read_end       = read_end + FFMIN(buf + buf_size - read_end,
00559                                               nb_desired * FLAC_AVG_FRAME_SIZE);
00560         }
00561 
00562         /* Fill the buffer. */
00563         if (av_fifo_realloc2(fpc->fifo_buf,
00564                              (read_end - read_start) + av_fifo_size(fpc->fifo_buf)) < 0) {
00565             av_log(avctx, AV_LOG_ERROR,
00566                    "couldn't reallocate buffer of size %td\n",
00567                    (read_end - read_start) + av_fifo_size(fpc->fifo_buf));
00568             goto handle_error;
00569         }
00570 
00571         if (buf) {
00572             av_fifo_generic_write(fpc->fifo_buf, (void*) read_start,
00573                                   read_end - read_start, NULL);
00574         } else {
00575             int8_t pad[MAX_FRAME_HEADER_SIZE];
00576             memset(pad, 0, sizeof(pad));
00577             av_fifo_generic_write(fpc->fifo_buf, (void*) pad, sizeof(pad), NULL);
00578         }
00579 
00580         /* Tag headers and update sequences. */
00581         start_offset = av_fifo_size(fpc->fifo_buf) -
00582                        ((read_end - read_start) + (MAX_FRAME_HEADER_SIZE - 1));
00583         start_offset = FFMAX(0, start_offset);
00584         nb_headers   = find_new_headers(fpc, start_offset);
00585 
00586         if (nb_headers < 0) {
00587             av_log(avctx, AV_LOG_ERROR,
00588                    "find_new_headers couldn't allocate FLAC header\n");
00589             goto handle_error;
00590         }
00591 
00592         fpc->nb_headers_buffered = nb_headers;
00593         /* Wait till FLAC_MIN_HEADERS to output a valid frame. */
00594         if (!fpc->end_padded && fpc->nb_headers_buffered < FLAC_MIN_HEADERS) {
00595             if (buf && read_end < buf + buf_size) {
00596                 read_start = read_end;
00597                 continue;
00598             } else {
00599                 goto handle_error;
00600             }
00601         }
00602 
00603         /* If headers found, update the scores since we have longer chains. */
00604         if (fpc->end_padded || fpc->nb_headers_found)
00605             score_sequences(fpc);
00606 
00607         /* restore the state pre-padding */
00608         if (fpc->end_padded) {
00609             /* HACK: drain the tail of the fifo */
00610             fpc->fifo_buf->wptr -= MAX_FRAME_HEADER_SIZE;
00611             fpc->fifo_buf->wndx -= MAX_FRAME_HEADER_SIZE;
00612             if (fpc->fifo_buf->wptr < 0) {
00613                 fpc->fifo_buf->wptr += fpc->fifo_buf->end -
00614                     fpc->fifo_buf->buffer;
00615             }
00616             buf_size = 0;
00617             read_start = read_end = NULL;
00618         }
00619     }
00620 
00621     curr = fpc->headers;
00622     for (curr = fpc->headers; curr; curr = curr->next)
00623         if (!fpc->best_header || curr->max_score > fpc->best_header->max_score)
00624             fpc->best_header = curr;
00625 
00626     if (fpc->best_header) {
00627         fpc->best_header_valid = 1;
00628         if (fpc->best_header->offset > 0) {
00629             /* Output a junk frame. */
00630             av_log(avctx, AV_LOG_DEBUG, "Junk frame till offset %i\n",
00631                    fpc->best_header->offset);
00632 
00633             /* Set frame_size to 0. It is unknown or invalid in a junk frame. */
00634             avctx->frame_size = 0;
00635             *poutbuf_size     = fpc->best_header->offset;
00636             *poutbuf          = flac_fifo_read_wrap(fpc, 0, *poutbuf_size,
00637                                                     &fpc->wrap_buf,
00638                                                     &fpc->wrap_buf_allocated_size);
00639             return buf_size ? (read_end - buf) : (fpc->best_header->offset -
00640                                            av_fifo_size(fpc->fifo_buf));
00641         }
00642         if (!buf_size)
00643             return get_best_header(fpc, poutbuf, poutbuf_size);
00644     }
00645 
00646 handle_error:
00647     *poutbuf      = NULL;
00648     *poutbuf_size = 0;
00649     return read_end - buf;
00650 }
00651 
00652 static int flac_parse_init(AVCodecParserContext *c)
00653 {
00654     FLACParseContext *fpc = c->priv_data;
00655     /* There will generally be FLAC_MIN_HEADERS buffered in the fifo before
00656        it drains.  This is allocated early to avoid slow reallocation. */
00657     fpc->fifo_buf = av_fifo_alloc(FLAC_AVG_FRAME_SIZE * (FLAC_MIN_HEADERS + 3));
00658     return 0;
00659 }
00660 
00661 static void flac_parse_close(AVCodecParserContext *c)
00662 {
00663     FLACParseContext *fpc = c->priv_data;
00664     FLACHeaderMarker *curr = fpc->headers, *temp;
00665 
00666     while (curr) {
00667         temp = curr->next;
00668         av_freep(&curr->link_penalty);
00669         av_free(curr);
00670         curr = temp;
00671     }
00672     av_fifo_free(fpc->fifo_buf);
00673     av_free(fpc->wrap_buf);
00674 }
00675 
00676 AVCodecParser ff_flac_parser = {
00677     { CODEC_ID_FLAC },
00678     sizeof(FLACParseContext),
00679     flac_parse_init,
00680     flac_parse,
00681     flac_parse_close,
00682 };