/*
* 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 it's crc-verified
* children, penalized by changes in sample rate, frame number, etc.
* The parser returns the frame with the highest score.
**/
#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 {
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);
}
fpc->avctx->sample_rate = header->fi.samplerate;
fpc->avctx->channels = header->fi.channels;
fpc->avctx->frame_size = 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))
avctx->frame_size = 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);
}
/* 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];
memset(pad, 0, sizeof(pad));
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 frame_size to 0. It is unknown or invalid in a junk frame. */
avctx->frame_size = 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 int flac_parse_init(AVCodecParserContext *c)
{
FLACParseContext *fpc = c->priv_data;
/* 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 = { CODEC_ID_FLAC },
.priv_data_size = sizeof(FLACParseContext),
.parser_init = flac_parse_init,
.parser_parse = flac_parse,
.parser_close = flac_parse_close,
};