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codecs: mpa: Improve seek & resume accuracy for VBR files

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The codec used 32-bit math for elapsed time <-> file position
calculations. The rounding errors seem to be the cause of poor
seek/resume accuracy on long VBR files; switching to 64-bit math
makes things much better.

Change-Id: Iba638d9e031a891022510c31c141cc4541e3f149
This commit is contained in:
Aidan MacDonald 2022-10-31 11:47:37 +00:00
parent 26ffcd8f9f
commit 4e60fb77e0
1 changed files with 32 additions and 55 deletions
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87
lib/rbcodec/codecs/mpa.c
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@ -176,38 +176,27 @@ static int get_file_pos(int newtime)
struct mp3entry *id3 = ci->id3;
if (id3->vbr) {
/* Convert newtime and id3->length to seconds to
* avoid overflow */
unsigned int newtime_s = newtime/1000;
unsigned int length_s = id3->length/1000;
if (id3->has_toc) {
/* Use the TOC to find the new position */
unsigned int percent, remainder;
int curtoc, nexttoc, plen;
percent = (newtime_s*100) / length_s;
unsigned int percent = ((uint64_t)newtime * 100) / id3->length;
if (percent > 99)
percent = 99;
curtoc = id3->toc[percent];
unsigned int pct_timestep = id3->length / 100;
unsigned int toc_sizestep = id3->filesize / 256;
unsigned int cur_toc = id3->toc[percent];
unsigned int next_toc = percent < 99 ? id3->toc[percent+1] : 256;
unsigned int plength = (next_toc - cur_toc) * toc_sizestep;
if (percent < 99) {
nexttoc = id3->toc[percent+1];
} else {
nexttoc = 256;
}
/* Seek to TOC mark */
pos = cur_toc * toc_sizestep;
pos = (id3->filesize/256)*curtoc;
/* Use the remainder to get a more accurate position */
remainder = (newtime_s*100) % length_s;
remainder = (remainder*100) / length_s;
plen = (nexttoc - curtoc)*(id3->filesize/256);
pos += (plen/100)*remainder;
/* Interpolate between this TOC mark and the next TOC mark */
newtime -= percent * pct_timestep;
pos += (uint64_t)plength * newtime / pct_timestep;
} else {
/* No TOC exists, estimate the new position */
pos = (id3->filesize / length_s) * newtime_s;
pos = (uint64_t)newtime * id3->filesize / id3->length;
}
} else if (id3->bitrate) {
pos = newtime * (id3->bitrate / 8);
@ -234,43 +223,31 @@ static void set_elapsed(struct mp3entry* id3)
if ( id3->vbr ) {
if ( id3->has_toc ) {
/* calculate elapsed time using TOC */
int i;
unsigned int remainder, plen, relpos, nextpos;
unsigned int pct_timestep = id3->length / 100;
unsigned int toc_sizestep = id3->filesize / 256;
/* find wich percent we're at */
for (i=0; i<100; i++ )
if ( offset < id3->toc[i] * (id3->filesize / 256) )
int percent;
for (percent = 0; percent < 100; ++percent)
if (offset < id3->toc[percent] * toc_sizestep)
break;
if (percent > 0)
--percent;
i--;
if (i < 0)
i = 0;
unsigned int cur_toc = id3->toc[percent];
unsigned int next_toc = percent < 99 ? id3->toc[percent+1] : 256;
unsigned int plength = (next_toc - cur_toc) * toc_sizestep;
relpos = id3->toc[i];
/* Set elapsed time to the TOC mark */
elapsed = percent * pct_timestep;
if (i < 99)
nextpos = id3->toc[i+1];
else
nextpos = 256;
remainder = offset - (relpos * (id3->filesize / 256));
/* set time for this percent (divide before multiply to prevent
overflow on long files. loss of precision is negligible on
short files) */
elapsed = i * (id3->length / 100);
/* calculate remainder time */
plen = (nextpos - relpos) * (id3->filesize / 256);
elapsed += (((remainder * 100) / plen) * (id3->length / 10000));
}
else {
/* no TOC exists. set a rough estimate using average bitrate */
int tpk = id3->length /
((id3->filesize - id3->first_frame_offset - id3->id3v1len) /
1024);
elapsed = offset / 1024 * tpk;
/* Interpolate between this TOC mark and the next TOC mark */
offset -= cur_toc * toc_sizestep;
elapsed += (uint64_t)pct_timestep * offset / plength;
} else {
/* No TOC, use an approximation (this'll be wildly inaccurate) */
uint64_t data_size = id3->filesize -
id3->first_frame_offset - id3->id3v1len;
elapsed = (uint64_t)id3->length * offset / data_size;
}
}
else