/* * FLAC parser * Copyright (c) 2010 Michael Chinen * * This file is part of Libav. * * Libav is free software; you can redistribute it and/or * modify it under the terms of the GNU Lesser General Public * License as published by the Free Software Foundation; either * version 2.1 of the License, or (at your option) any later version. * * Libav is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU * Lesser General Public License for more details. * * You should have received a copy of the GNU Lesser General Public * License along with Libav; if not, write to the Free Software * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA */ /** * @file * FLAC parser * * The FLAC parser buffers input until FLAC_MIN_HEADERS has been found. * Each time it finds and verifies a CRC-8 header it sees which of the * FLAC_MAX_SEQUENTIAL_HEADERS that came before it have a valid CRC-16 footer * that ends at the newly found header. * Headers are scored by FLAC_HEADER_BASE_SCORE plus the max of its crc-verified * children, penalized by changes in sample rate, frame number, etc. * The parser returns the frame with the highest score. **/ #include "libavutil/attributes.h" #include "libavutil/crc.h" #include "libavutil/fifo.h" #include "bytestream.h" #include "parser.h" #include "flac.h" /** maximum number of adjacent headers that compare CRCs against each other */ #define FLAC_MAX_SEQUENTIAL_HEADERS 3 /** minimum number of headers buffered and checked before returning frames */ #define FLAC_MIN_HEADERS 10 /** estimate for average size of a FLAC frame */ #define FLAC_AVG_FRAME_SIZE 8192 /** scoring settings for score_header */ #define FLAC_HEADER_BASE_SCORE 10 #define FLAC_HEADER_CHANGED_PENALTY 7 #define FLAC_HEADER_CRC_FAIL_PENALTY 50 #define FLAC_HEADER_NOT_PENALIZED_YET 100000 #define FLAC_HEADER_NOT_SCORED_YET -100000 /** largest possible size of flac header */ #define MAX_FRAME_HEADER_SIZE 16 typedef struct FLACHeaderMarker { int offset; /**< byte offset from start of FLACParseContext->buffer */ int *link_penalty; /**< pointer to array of local scores between this header and the one at a distance equal array position */ int max_score; /**< maximum score found after checking each child that has a valid CRC */ FLACFrameInfo fi; /**< decoded frame header info */ struct FLACHeaderMarker *next; /**< next CRC-8 verified header that immediately follows this one in the bytestream */ struct FLACHeaderMarker *best_child; /**< following frame header with which this frame has the best score with */ } FLACHeaderMarker; typedef struct FLACParseContext { AVCodecParserContext *pc; /**< parent context */ AVCodecContext *avctx; /**< codec context pointer for logging */ FLACHeaderMarker *headers; /**< linked-list that starts at the first CRC-8 verified header within buffer */ FLACHeaderMarker *best_header; /**< highest scoring header within buffer */ int nb_headers_found; /**< number of headers found in the last flac_parse() call */ int nb_headers_buffered; /**< number of headers that are buffered */ int best_header_valid; /**< flag set when the parser returns junk; if set return best_header next time */ AVFifoBuffer *fifo_buf; /**< buffer to store all data until headers can be verified */ int end_padded; /**< specifies if fifo_buf's end is padded */ uint8_t *wrap_buf; /**< general fifo read buffer when wrapped */ int wrap_buf_allocated_size; /**< actual allocated size of the buffer */ } FLACParseContext; static int frame_header_is_valid(AVCodecContext *avctx, const uint8_t *buf, FLACFrameInfo *fi) { GetBitContext gb; init_get_bits(&gb, buf, MAX_FRAME_HEADER_SIZE * 8); return !ff_flac_decode_frame_header(avctx, &gb, fi, 127); } /** * Non-destructive fast fifo pointer fetching * Returns a pointer from the specified offset. * If possible the pointer points within the fifo buffer. * Otherwise (if it would cause a wrap around,) a pointer to a user-specified * buffer is used. * The pointer can be NULL. In any case it will be reallocated to hold the size. * If the returned pointer will be used after subsequent calls to flac_fifo_read_wrap * then the subsequent calls should pass in a different wrap_buf so as to not * overwrite the contents of the previous wrap_buf. * This function is based on av_fifo_generic_read, which is why there is a comment * about a memory barrier for SMP. */ static uint8_t* flac_fifo_read_wrap(FLACParseContext *fpc, int offset, int len, uint8_t** wrap_buf, int* allocated_size) { AVFifoBuffer *f = fpc->fifo_buf; uint8_t *start = f->rptr + offset; uint8_t *tmp_buf; if (start >= f->end) start -= f->end - f->buffer; if (f->end - start >= len) return start; tmp_buf = av_fast_realloc(*wrap_buf, allocated_size, len); if (!tmp_buf) { av_log(fpc->avctx, AV_LOG_ERROR, "couldn't reallocate wrap buffer of size %d", len); return NULL; } *wrap_buf = tmp_buf; do { int seg_len = FFMIN(f->end - start, len); memcpy(tmp_buf, start, seg_len); tmp_buf = (uint8_t*)tmp_buf + seg_len; // memory barrier needed for SMP here in theory start += seg_len - (f->end - f->buffer); len -= seg_len; } while (len > 0); return *wrap_buf; } /** * Return a pointer in the fifo buffer where the offset starts at until * the wrap point or end of request. * len will contain the valid length of the returned buffer. * A second call to flac_fifo_read (with new offset and len) should be called * to get the post-wrap buf if the returned len is less than the requested. **/ static uint8_t* flac_fifo_read(FLACParseContext *fpc, int offset, int *len) { AVFifoBuffer *f = fpc->fifo_buf; uint8_t *start = f->rptr + offset; if (start >= f->end) start -= f->end - f->buffer; *len = FFMIN(*len, f->end - start); return start; } static int find_headers_search_validate(FLACParseContext *fpc, int offset) { FLACFrameInfo fi; uint8_t *header_buf; int size = 0; header_buf = flac_fifo_read_wrap(fpc, offset, MAX_FRAME_HEADER_SIZE, &fpc->wrap_buf, &fpc->wrap_buf_allocated_size); if (frame_header_is_valid(fpc->avctx, header_buf, &fi)) { FLACHeaderMarker **end_handle = &fpc->headers; int i; size = 0; while (*end_handle) { end_handle = &(*end_handle)->next; size++; } *end_handle = av_mallocz(sizeof(FLACHeaderMarker)); if (!*end_handle) { av_log(fpc->avctx, AV_LOG_ERROR, "couldn't allocate FLACHeaderMarker\n"); return AVERROR(ENOMEM); } (*end_handle)->fi = fi; (*end_handle)->offset = offset; (*end_handle)->link_penalty = av_malloc(sizeof(int) * FLAC_MAX_SEQUENTIAL_HEADERS); for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++) (*end_handle)->link_penalty[i] = FLAC_HEADER_NOT_PENALIZED_YET; fpc->nb_headers_found++; size++; } return size; } static int find_headers_search(FLACParseContext *fpc, uint8_t *buf, int buf_size, int search_start) { int size = 0, mod_offset = (buf_size - 1) % 4, i, j; uint32_t x; for (i = 0; i < mod_offset; i++) { if ((AV_RB16(buf + i) & 0xFFFE) == 0xFFF8) size = find_headers_search_validate(fpc, search_start + i); } for (; i < buf_size - 1; i += 4) { x = AV_RB32(buf + i); if (((x & ~(x + 0x01010101)) & 0x80808080)) { for (j = 0; j < 4; j++) { if ((AV_RB16(buf + i + j) & 0xFFFE) == 0xFFF8) size = find_headers_search_validate(fpc, search_start + i + j); } } } return size; } static int find_new_headers(FLACParseContext *fpc, int search_start) { FLACHeaderMarker *end; int search_end, size = 0, read_len, temp; uint8_t *buf; fpc->nb_headers_found = 0; /* Search for a new header of at most 16 bytes. */ search_end = av_fifo_size(fpc->fifo_buf) - (MAX_FRAME_HEADER_SIZE - 1); read_len = search_end - search_start + 1; buf = flac_fifo_read(fpc, search_start, &read_len); size = find_headers_search(fpc, buf, read_len, search_start); search_start += read_len - 1; /* If fifo end was hit do the wrap around. */ if (search_start != search_end) { uint8_t wrap[2]; wrap[0] = buf[read_len - 1]; read_len = search_end - search_start + 1; /* search_start + 1 is the post-wrap offset in the fifo. */ buf = flac_fifo_read(fpc, search_start + 1, &read_len); wrap[1] = buf[0]; if ((AV_RB16(wrap) & 0xFFFE) == 0xFFF8) { temp = find_headers_search_validate(fpc, search_start); size = FFMAX(size, temp); } search_start++; /* Continue to do the last half of the wrap. */ temp = find_headers_search(fpc, buf, read_len, search_start); size = FFMAX(size, temp); search_start += read_len - 1; } /* Return the size even if no new headers were found. */ if (!size && fpc->headers) for (end = fpc->headers; end; end = end->next) size++; return size; } static int check_header_mismatch(FLACParseContext *fpc, FLACHeaderMarker *header, FLACHeaderMarker *child, int log_level_offset) { FLACFrameInfo *header_fi = &header->fi, *child_fi = &child->fi; int deduction = 0, deduction_expected = 0, i; if (child_fi->samplerate != header_fi->samplerate) { deduction += FLAC_HEADER_CHANGED_PENALTY; av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset, "sample rate change detected in adjacent frames\n"); } if (child_fi->bps != header_fi->bps) { deduction += FLAC_HEADER_CHANGED_PENALTY; av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset, "bits per sample change detected in adjacent frames\n"); } if (child_fi->is_var_size != header_fi->is_var_size) { /* Changing blocking strategy not allowed per the spec */ deduction += FLAC_HEADER_BASE_SCORE; av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset, "blocking strategy change detected in adjacent frames\n"); } if (child_fi->channels != header_fi->channels) { deduction += FLAC_HEADER_CHANGED_PENALTY; av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset, "number of channels change detected in adjacent frames\n"); } /* Check sample and frame numbers. */ if ((child_fi->frame_or_sample_num - header_fi->frame_or_sample_num != header_fi->blocksize) && (child_fi->frame_or_sample_num != header_fi->frame_or_sample_num + 1)) { FLACHeaderMarker *curr; int expected_frame_num, expected_sample_num; /* If there are frames in the middle we expect this deduction, as they are probably valid and this one follows it */ expected_frame_num = expected_sample_num = header_fi->frame_or_sample_num; curr = header; while (curr != child) { /* Ignore frames that failed all crc checks */ for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS; i++) { if (curr->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY) { expected_frame_num++; expected_sample_num += curr->fi.blocksize; break; } } curr = curr->next; } if (expected_frame_num == child_fi->frame_or_sample_num || expected_sample_num == child_fi->frame_or_sample_num) deduction_expected = deduction ? 0 : 1; deduction += FLAC_HEADER_CHANGED_PENALTY; av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset, "sample/frame number mismatch in adjacent frames\n"); } /* If we have suspicious headers, check the CRC between them */ if (deduction && !deduction_expected) { FLACHeaderMarker *curr; int read_len; uint8_t *buf; uint32_t crc = 1; int inverted_test = 0; /* Since CRC is expensive only do it if we haven't yet. This assumes a CRC penalty is greater than all other check penalties */ curr = header->next; for (i = 0; i < FLAC_MAX_SEQUENTIAL_HEADERS && curr != child; i++) curr = curr->next; if (header->link_penalty[i] < FLAC_HEADER_CRC_FAIL_PENALTY || header->link_penalty[i] == FLAC_HEADER_NOT_PENALIZED_YET) { FLACHeaderMarker *start, *end; /* Although overlapping chains are scored, the crc should never have to be computed twice for a single byte. */ start = header; end = child; if (i > 0 && header->link_penalty[i - 1] >= FLAC_HEADER_CRC_FAIL_PENALTY) { while (start->next != child) start = start->next; inverted_test = 1; } else if (i > 0 && header->next->link_penalty[i-1] >= FLAC_HEADER_CRC_FAIL_PENALTY ) { end = header->next; inverted_test = 1; } read_len = end->offset - start->offset; buf = flac_fifo_read(fpc, start->offset, &read_len); crc = av_crc(av_crc_get_table(AV_CRC_16_ANSI), 0, buf, read_len); read_len = (end->offset - start->offset) - read_len; if (read_len) { buf = flac_fifo_read(fpc, end->offset - read_len, &read_len); crc = av_crc(av_crc_get_table(AV_CRC_16_ANSI), crc, buf, read_len); } } if (!crc ^ !inverted_test) { deduction += FLAC_HEADER_CRC_FAIL_PENALTY; av_log(fpc->avctx, AV_LOG_WARNING + log_level_offset, "crc check failed from offset %i (frame %"PRId64") to %i (frame %"PRId64")\n", header->offset, header_fi->frame_or_sample_num, child->offset, child_fi->frame_or_sample_num); } } return deduction; } /** * Score a header. * * Give FLAC_HEADER_BASE_SCORE points to a frame for existing. * If it has children, (subsequent frames of which the preceding CRC footer * validates against this one,) then take the maximum score of the children, * with a penalty of FLAC_HEADER_CHANGED_PENALTY applied for each change to * bps, sample rate, channels, but not decorrelation mode, or blocksize, * because it can change often. **/ static int score_header(FLACParseContext *fpc, FLACHeaderMarker *header) { FLACHeaderMarker *child; int dist = 0; int child_score; if (header->max_score != FLAC_HEADER_NOT_SCORED_YET) return header->max_score; header->max_score = FLAC_HEADER_BASE_SCORE; /* Check and compute the children's scores. */ child = header->next; for (dist = 0; dist < FLAC_MAX_SEQUENTIAL_HEADERS && child; dist++) { /* Look at the child's frame header info and penalize suspicious changes between the headers. */ if (header->link_penalty[dist] == FLAC_HEADER_NOT_PENALIZED_YET) { header->link_penalty[dist] = check_header_mismatch(fpc, header, child, AV_LOG_DEBUG); } child_score = score_header(fpc, child) - header->link_penalty[dist]; if (FLAC_HEADER_BASE_SCORE + child_score > header->max_score) { /* Keep the child because the frame scoring is dynamic. */ header->best_child = child; header->max_score = FLAC_HEADER_BASE_SCORE + child_score; } child = child->next; } return header->max_score; } static void score_sequences(FLACParseContext *fpc) { FLACHeaderMarker *curr; int best_score = FLAC_HEADER_NOT_SCORED_YET; /* First pass to clear all old scores. */ for (curr = fpc->headers; curr; curr = curr->next) curr->max_score = FLAC_HEADER_NOT_SCORED_YET; /* Do a second pass to score them all. */ for (curr = fpc->headers; curr; curr = curr->next) { if (score_header(fpc, curr) > best_score) { fpc->best_header = curr; best_score = curr->max_score; } } } static int get_best_header(FLACParseContext* fpc, const uint8_t **poutbuf, int *poutbuf_size) { FLACHeaderMarker *header = fpc->best_header; FLACHeaderMarker *child = header->best_child; if (!child) { *poutbuf_size = av_fifo_size(fpc->fifo_buf) - header->offset; } else { *poutbuf_size = child->offset - header->offset; /* If the child has suspicious changes, log them */ check_header_mismatch(fpc, header, child, 0); } if (header->fi.channels != fpc->avctx->channels || !fpc->avctx->channel_layout) { fpc->avctx->channels = header->fi.channels; ff_flac_set_channel_layout(fpc->avctx); } fpc->avctx->sample_rate = header->fi.samplerate; fpc->pc->duration = header->fi.blocksize; *poutbuf = flac_fifo_read_wrap(fpc, header->offset, *poutbuf_size, &fpc->wrap_buf, &fpc->wrap_buf_allocated_size); fpc->best_header_valid = 0; /* Return the negative overread index so the client can compute pos. This should be the amount overread to the beginning of the child */ if (child) return child->offset - av_fifo_size(fpc->fifo_buf); return 0; } static int flac_parse(AVCodecParserContext *s, AVCodecContext *avctx, const uint8_t **poutbuf, int *poutbuf_size, const uint8_t *buf, int buf_size) { FLACParseContext *fpc = s->priv_data; FLACHeaderMarker *curr; int nb_headers; const uint8_t *read_end = buf; const uint8_t *read_start = buf; if (s->flags & PARSER_FLAG_COMPLETE_FRAMES) { FLACFrameInfo fi; if (frame_header_is_valid(avctx, buf, &fi)) s->duration = fi.blocksize; *poutbuf = buf; *poutbuf_size = buf_size; return buf_size; } fpc->avctx = avctx; if (fpc->best_header_valid) return get_best_header(fpc, poutbuf, poutbuf_size); /* If a best_header was found last call remove it with the buffer data. */ if (fpc->best_header && fpc->best_header->best_child) { FLACHeaderMarker *temp; FLACHeaderMarker *best_child = fpc->best_header->best_child; /* Remove headers in list until the end of the best_header. */ for (curr = fpc->headers; curr != best_child; curr = temp) { if (curr != fpc->best_header) { av_log(avctx, AV_LOG_DEBUG, "dropping low score %i frame header from offset %i to %i\n", curr->max_score, curr->offset, curr->next->offset); } temp = curr->next; av_freep(&curr->link_penalty); av_free(curr); fpc->nb_headers_buffered--; } /* Release returned data from ring buffer. */ av_fifo_drain(fpc->fifo_buf, best_child->offset); /* Fix the offset for the headers remaining to match the new buffer. */ for (curr = best_child->next; curr; curr = curr->next) curr->offset -= best_child->offset; fpc->nb_headers_buffered--; best_child->offset = 0; fpc->headers = best_child; if (fpc->nb_headers_buffered >= FLAC_MIN_HEADERS) { fpc->best_header = best_child; return get_best_header(fpc, poutbuf, poutbuf_size); } fpc->best_header = NULL; } else if (fpc->best_header) { /* No end frame no need to delete the buffer; probably eof */ FLACHeaderMarker *temp; for (curr = fpc->headers; curr != fpc->best_header; curr = temp) { temp = curr->next; av_freep(&curr->link_penalty); av_free(curr); } fpc->headers = fpc->best_header->next; av_freep(&fpc->best_header->link_penalty); av_freep(&fpc->best_header); } /* Find and score new headers. */ while ((buf && read_end < buf + buf_size && fpc->nb_headers_buffered < FLAC_MIN_HEADERS) || (!buf && !fpc->end_padded)) { int start_offset; /* Pad the end once if EOF, to check the final region for headers. */ if (!buf) { fpc->end_padded = 1; buf_size = MAX_FRAME_HEADER_SIZE; read_end = read_start + MAX_FRAME_HEADER_SIZE; } else { /* The maximum read size is the upper-bound of what the parser needs to have the required number of frames buffered */ int nb_desired = FLAC_MIN_HEADERS - fpc->nb_headers_buffered + 1; read_end = read_end + FFMIN(buf + buf_size - read_end, nb_desired * FLAC_AVG_FRAME_SIZE); } if (!av_fifo_space(fpc->fifo_buf) && av_fifo_size(fpc->fifo_buf) / FLAC_AVG_FRAME_SIZE > fpc->nb_headers_buffered * 10) { /* There is less than one valid flac header buffered for 10 headers * buffered. Therefore the fifo is most likely filled with invalid * data and the input is not a flac file. */ goto handle_error; } /* Fill the buffer. */ if (av_fifo_realloc2(fpc->fifo_buf, (read_end - read_start) + av_fifo_size(fpc->fifo_buf)) < 0) { av_log(avctx, AV_LOG_ERROR, "couldn't reallocate buffer of size %td\n", (read_end - read_start) + av_fifo_size(fpc->fifo_buf)); goto handle_error; } if (buf) { av_fifo_generic_write(fpc->fifo_buf, (void*) read_start, read_end - read_start, NULL); } else { int8_t pad[MAX_FRAME_HEADER_SIZE] = { 0 }; av_fifo_generic_write(fpc->fifo_buf, (void*) pad, sizeof(pad), NULL); } /* Tag headers and update sequences. */ start_offset = av_fifo_size(fpc->fifo_buf) - ((read_end - read_start) + (MAX_FRAME_HEADER_SIZE - 1)); start_offset = FFMAX(0, start_offset); nb_headers = find_new_headers(fpc, start_offset); if (nb_headers < 0) { av_log(avctx, AV_LOG_ERROR, "find_new_headers couldn't allocate FLAC header\n"); goto handle_error; } fpc->nb_headers_buffered = nb_headers; /* Wait till FLAC_MIN_HEADERS to output a valid frame. */ if (!fpc->end_padded && fpc->nb_headers_buffered < FLAC_MIN_HEADERS) { if (buf && read_end < buf + buf_size) { read_start = read_end; continue; } else { goto handle_error; } } /* If headers found, update the scores since we have longer chains. */ if (fpc->end_padded || fpc->nb_headers_found) score_sequences(fpc); /* restore the state pre-padding */ if (fpc->end_padded) { /* HACK: drain the tail of the fifo */ fpc->fifo_buf->wptr -= MAX_FRAME_HEADER_SIZE; fpc->fifo_buf->wndx -= MAX_FRAME_HEADER_SIZE; if (fpc->fifo_buf->wptr < 0) { fpc->fifo_buf->wptr += fpc->fifo_buf->end - fpc->fifo_buf->buffer; } buf_size = 0; read_start = read_end = NULL; } } curr = fpc->headers; for (curr = fpc->headers; curr; curr = curr->next) if (!fpc->best_header || curr->max_score > fpc->best_header->max_score) fpc->best_header = curr; if (fpc->best_header) { fpc->best_header_valid = 1; if (fpc->best_header->offset > 0) { /* Output a junk frame. */ av_log(avctx, AV_LOG_DEBUG, "Junk frame till offset %i\n", fpc->best_header->offset); /* Set duration to 0. It is unknown or invalid in a junk frame. */ s->duration = 0; *poutbuf_size = fpc->best_header->offset; *poutbuf = flac_fifo_read_wrap(fpc, 0, *poutbuf_size, &fpc->wrap_buf, &fpc->wrap_buf_allocated_size); return buf_size ? (read_end - buf) : (fpc->best_header->offset - av_fifo_size(fpc->fifo_buf)); } if (!buf_size) return get_best_header(fpc, poutbuf, poutbuf_size); } handle_error: *poutbuf = NULL; *poutbuf_size = 0; return read_end - buf; } static av_cold int flac_parse_init(AVCodecParserContext *c) { FLACParseContext *fpc = c->priv_data; fpc->pc = c; /* There will generally be FLAC_MIN_HEADERS buffered in the fifo before it drains. This is allocated early to avoid slow reallocation. */ fpc->fifo_buf = av_fifo_alloc(FLAC_AVG_FRAME_SIZE * (FLAC_MIN_HEADERS + 3)); return 0; } static void flac_parse_close(AVCodecParserContext *c) { FLACParseContext *fpc = c->priv_data; FLACHeaderMarker *curr = fpc->headers, *temp; while (curr) { temp = curr->next; av_freep(&curr->link_penalty); av_free(curr); curr = temp; } av_fifo_free(fpc->fifo_buf); av_free(fpc->wrap_buf); } AVCodecParser ff_flac_parser = { .codec_ids = { AV_CODEC_ID_FLAC }, .priv_data_size = sizeof(FLACParseContext), .parser_init = flac_parse_init, .parser_parse = flac_parse, .parser_close = flac_parse_close, };