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Fix MP4 frame offset calculation #96

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merged 1 commit into from
Apr 19, 2023
Merged

Fix MP4 frame offset calculation #96

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4 changes: 2 additions & 2 deletions frontend/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -909,7 +909,7 @@ static int decodeMP4file(char *mp4file, char *sndfile, char *adts_fn, int to_std
startSampleId = (int64_t)(seek_to * mp4config.samplerate / framesize);

mp4read_seek(startSampleId);
for (sampleId = startSampleId; sampleId < mp4config.frame.ents; sampleId++)
for (sampleId = startSampleId; sampleId < mp4config.frame.nsamples; sampleId++)
{
/*int rc;*/
long dur;
Expand Down Expand Up @@ -991,7 +991,7 @@ static int decodeMP4file(char *mp4file, char *sndfile, char *adts_fn, int to_std
first_time = 0;
}

percent = min((int)(sampleId*100)/mp4config.frame.ents, 100);
percent = min((int)(sampleId*100)/mp4config.frame.nsamples, 100);
if (percent > old_percent)
{
old_percent = percent;
Expand Down
190 changes: 150 additions & 40 deletions frontend/mp4read.c
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Original file line number Diff line number Diff line change
Expand Up @@ -78,6 +78,15 @@ static inline uint16_t bswap16(const uint16_t u16)

enum {ERR_OK = 0, ERR_FAIL = -1, ERR_UNSUPPORTED = -2};

static void freeMem(void** address)
{
if (*address)
{
free(*address);
*address = 0;
}
}

static int datain(void *data, int size)
{
if (fread(data, 1, size, g_fin) != size)
Expand Down Expand Up @@ -325,64 +334,163 @@ static int esdsin(int size)
return size;
}

/* stbl "Sample Table" layout:
* - stts "Time-to-Sample" - useless
* - stsc "Sample-to-Chunk" - condensed table chunk-to-num-samples
* - stsz "Sample Size" - size table
* - stco "Chunk Offset" - chunk starts
*
* When receiving stco we can combine stsc and stsz tables to produce final
* sample offsets.
*/

static int sttsin(int size)
{
if (size < 16) //min stts size
uint32_t ntts;

if (size < 8)
return ERR_FAIL;

// version/flags
u32in();
ntts = u32in();

if (ntts < 1)
return ERR_FAIL;

/* 2 x uint32_t per entry */
if (((size - 8u) / 8u) < ntts)
return ERR_FAIL;

return size;
}

static int stszin(int size)
static int stscin(int size)
{
int cnt;
uint32_t ofs;
uint32_t i, tmp, firstchunk, prevfirstchunk, samplesperchunk;

if (size < 8)
return ERR_FAIL;

// version/flags
u32in();
// Sample size
u32in();
// Number of entries
mp4config.frame.ents = u32in();

if (!(mp4config.frame.ents + 1))
mp4config.frame.nsclices = u32in();

tmp = sizeof(slice_info_t) * mp4config.frame.nsclices;
if (tmp < mp4config.frame.nsclices)
return ERR_FAIL;
mp4config.frame.map = malloc(tmp);
if (!mp4config.frame.map)
return ERR_FAIL;

mp4config.frame.data = malloc(sizeof(*mp4config.frame.data)
* (mp4config.frame.ents + 1));
/* 3 x uint32_t per entry */
if (((size - 8u) / 12u) < mp4config.frame.nsclices)
return ERR_FAIL;

if (!mp4config.frame.data)
prevfirstchunk = 0;
for (i = 0; i < mp4config.frame.nsclices; ++i) {
firstchunk = u32in();
samplesperchunk = u32in();
// id - unused
u32in();
if (firstchunk <= prevfirstchunk)
return ERR_FAIL;
if (samplesperchunk < 1)
return ERR_FAIL;
mp4config.frame.map[i].firstchunk = firstchunk;
mp4config.frame.map[i].samplesperchunk = samplesperchunk;
prevfirstchunk = firstchunk;
}

ofs = 0;
mp4config.frame.data[0] = ofs;
for (cnt = 0; cnt < mp4config.frame.ents; cnt++)
{
uint32_t fsize = u32in();
return size;
}

static int stszin(int size)
{
uint32_t i, tmp;

ofs += fsize;
if (mp4config.frame.maxsize < fsize)
mp4config.frame.maxsize = fsize;
if (size < 12)
return ERR_FAIL;

// version/flags
u32in();
// (uniform) Sample size
// TODO(eustas): add uniform sample size support?
u32in();
mp4config.frame.nsamples = u32in();

mp4config.frame.data[cnt + 1] = ofs;
if (!mp4config.frame.nsamples)
return ERR_FAIL;

if (ofs < mp4config.frame.data[cnt])
return ERR_FAIL;
tmp = sizeof(frame_info_t) * mp4config.frame.nsamples;
if (tmp < mp4config.frame.nsamples)
return ERR_FAIL;
mp4config.frame.info = malloc(tmp);
if (!mp4config.frame.info)
return ERR_FAIL;

if ((size - 12u) / 4u < mp4config.frame.nsamples)
return ERR_FAIL;

for (i = 0; i < mp4config.frame.nsamples; i++)
{
mp4config.frame.info[i].len = u32in();
mp4config.frame.info[i].offset = 0;
if (mp4config.frame.maxsize < mp4config.frame.info[i].len)
mp4config.frame.maxsize = mp4config.frame.info[i].len;
}

return size;
}

static int stcoin(int size)
{
uint32_t numchunks, chunkstart, chunkn, slicen, samplesleft, i, offset;
uint32_t nextoffset;

if (size < 8)
return ERR_FAIL;

// version/flags
u32in();

// Number of entries
if (u32in() < 1)
numchunks = u32in();
if ((numchunks < 1) || ((numchunks + 1) == 0))
return ERR_FAIL;

if ((size - 8u) / 4u < numchunks)
return ERR_FAIL;
// first chunk offset
mp4config.mdatofs = u32in();
// ignore the rest

chunkn = 0;
samplesleft = 0;
slicen = 0;
offset = 0;

for (i = 0; i < mp4config.frame.nsamples; ++i) {
if (samplesleft == 0)
{
chunkn++;
if (chunkn > numchunks)
return ERR_FAIL;
if (slicen < mp4config.frame.nsclices)
{
if (chunkn == mp4config.frame.map[slicen + 1].firstchunk)
slicen++;
}
samplesleft = mp4config.frame.map[slicen].samplesperchunk;
offset = u32in();
}
mp4config.frame.info[i].offset = offset;
nextoffset = offset + mp4config.frame.info[i].len;
if (nextoffset < offset)
return ERR_FAIL;
offset = nextoffset;
samplesleft--;
}

freeMem(&mp4config.frame.map);

return size;
}
Expand Down Expand Up @@ -843,11 +951,12 @@ static int moovin(int sizemax)
{ATOM_NAME, "stts"},
{ATOM_DATA, sttsin},
{ATOM_NAME, "stsc"},
{ATOM_DATA, stscin}
{ATOM_NAME, "stsz"},
{ATOM_DATA, stszin},
{ATOM_NAME, "stco"},
{ATOM_DATA, stcoin},
{0}
{ATOM_STOP}
};

g_atom = mvhd;
Expand Down Expand Up @@ -926,18 +1035,20 @@ static creator_t g_meta2[] = {

int mp4read_frame(void)
{
if (mp4config.frame.current >= mp4config.frame.ents)
if (mp4config.frame.current >= mp4config.frame.nsamples)
return ERR_FAIL;

mp4config.bitbuf.size = mp4config.frame.data[mp4config.frame.current + 1]
- mp4config.frame.data[mp4config.frame.current];
// TODO(eustas): avoid no-op seeks
mp4read_seek(mp4config.frame.current);

mp4config.bitbuf.size = mp4config.frame.info[mp4config.frame.current].len;

if (fread(mp4config.bitbuf.data, 1, mp4config.bitbuf.size, g_fin)
!= mp4config.bitbuf.size)
{
fprintf(stderr, "can't read frame data(frame %d@0x%x)\n",
mp4config.frame.current,
mp4config.frame.data[mp4config.frame.current]);
mp4config.frame.info[mp4config.frame.current].offset);

return ERR_FAIL;
}
Expand All @@ -949,9 +1060,9 @@ int mp4read_frame(void)

int mp4read_seek(int framenum)
{
if (framenum > mp4config.frame.ents)
if (framenum > mp4config.frame.nsamples)
return ERR_FAIL;
if (fseek(g_fin, mp4config.mdatofs + mp4config.frame.data[framenum], SEEK_SET))
if (fseek(g_fin, mp4config.frame.info[framenum].offset, SEEK_SET))
return ERR_FAIL;

mp4config.frame.current = framenum;
Expand All @@ -969,18 +1080,17 @@ static void mp4info(void)
fprintf(stderr, "Buffer size:\t\t%d\n", mp4config.buffersize);
fprintf(stderr, "Max bitrate:\t\t%d\n", mp4config.bitratemax);
fprintf(stderr, "Average bitrate:\t%d\n", mp4config.bitrateavg);
fprintf(stderr, "Samples per frame:\t%d\n", mp4config.framesamples);
fprintf(stderr, "Frames:\t\t\t%d\n", mp4config.frame.ents);
fprintf(stderr, "Frames:\t\t\t%d\n", mp4config.frame.nsamples);
fprintf(stderr, "ASC size:\t\t%d\n", mp4config.asc.size);
fprintf(stderr, "Duration:\t\t%.1f sec\n", (float)mp4config.samples/mp4config.samplerate);
fprintf(stderr, "Data offset/size:\t%x/%x\n", mp4config.mdatofs, mp4config.mdatsize);
fprintf(stderr, "Data offset:\t%x\n", mp4config.frame.info[0].offset);
}

int mp4read_close(void)
{
#define FREE(x) if(x){free(x);x=0;}
FREE(mp4config.frame.data);
FREE(mp4config.bitbuf.data);
freeMem(&mp4config.frame.info);
freeMem(&mp4config.frame.map);
freeMem(&mp4config.bitbuf.data);

return ERR_OK;
}
Expand Down
22 changes: 17 additions & 5 deletions frontend/mp4read.h
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,18 @@

#include <stdint.h>

typedef struct
{
uint32_t len;
uint32_t offset;
} frame_info_t;

typedef struct
{
uint32_t firstchunk;
uint32_t samplesperchunk;
} slice_info_t;

typedef struct
{
uint32_t ctime, mtime;
Expand All @@ -32,11 +44,13 @@ typedef struct
uint16_t buffersize;
uint32_t bitratemax;
uint32_t bitrateavg;
uint32_t framesamples;
// frame size / offsets
struct
{
uint32_t *data;
uint32_t ents;
frame_info_t *info;
slice_info_t *map;
uint32_t nsamples;
uint32_t nsclices;
int current;
int maxsize;
} frame;
Expand All @@ -46,8 +60,6 @@ typedef struct
uint8_t buf[10];
int size;
} asc;
uint32_t mdatofs;
uint32_t mdatsize;
struct {
int size;
uint8_t *data;
Expand Down