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/*

 * FLAC parser

 * Copyright (c) 2010 Michael Chinen

 *

 * This file is part of FFmpeg.

 *

 * FFmpeg 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.

 *

 * FFmpeg 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 FFmpeg; 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   */

    FLACFrameInfo last_fi;         /**< last decoded frame header info        */

    int last_fi_valid;             /**< set if last_fi is valid               */

} 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_fi_mismatch(FLACParseContext  *fpc,

                                    FLACFrameInfo     *header_fi,

                                    FLACFrameInfo     *child_fi,

                                    int                log_level_offset)

{

    int deduction = 0;

    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");

    }

    return deduction;

}

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, deduction_expected = 0, i;

    deduction = check_header_fi_mismatch(fpc, header_fi, child_fi,

                                         log_level_offset);

    /* 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;

    int base_score = FLAC_HEADER_BASE_SCORE;

    if (header->max_score != FLAC_HEADER_NOT_SCORED_YET)

        return header->max_score;

    /* Modify the base score with changes from the last output header */

    if (fpc->last_fi_valid) {

        /* Silence the log since this will be repeated if selected */

        base_score -= check_header_fi_mismatch(fpc, &fpc->last_fi, &header->fi,

                                               AV_LOG_DEBUG);

    }

    header->max_score = 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  = base_score + child_score;

        }

        child = child->next;

    }

    return header->max_score;

}

static void score_sequences(FLACParseContext *fpc)

{

    FLACHeaderMarker *curr;

    int best_score = 0;//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;

    fpc->last_fi_valid = 1;

    fpc->last_fi = header->fi;

    /* 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;

            if (!avctx->sample_rate)

                avctx->sample_rate = fi.samplerate;

        }

        *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.                                     */

    /* buf_size is to zero when padding, so check for this since we do */

    /* not want to try to read more input once we have found the end.  */

    /* Note that as (non-modified) parameters, buf can be non-NULL,    */

    /* while buf_size is 0.                                            */

    while ((buf && buf_size && read_end < buf + buf_size &&

            fpc->nb_headers_buffered < FLAC_MIN_HEADERS)

           || ((!buf || !buf_size) && !fpc->end_padded)) {

        int start_offset;

        /* Pad the end once if EOF, to check the final region for headers. */

        if (!buf || !buf_size) {

            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);

        }

        /* Fill the buffer. */

        if (   av_fifo_space(fpc->fifo_buf) < read_end - read_start

            && av_fifo_realloc2(fpc->fifo_buf, (read_end - read_start) + 2*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 && buf_size) {

            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) {

            int warp = fpc->fifo_buf->wptr - fpc->fifo_buf->buffer < MAX_FRAME_HEADER_SIZE;

            /* HACK: drain the tail of the fifo */

            fpc->fifo_buf->wptr -= MAX_FRAME_HEADER_SIZE;

            fpc->fifo_buf->wndx -= MAX_FRAME_HEADER_SIZE;

            if (warp) {

                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 (curr->max_score > 0 &&

            (!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));

    if (!fpc->fifo_buf)

        return AVERROR(ENOMEM);

    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,

};