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decoder/ogg: improve seeking accuracy using binary search 

On some VBR files, the single-step interpolation was very inaccurate
and inacceptable.

Closes https://github.com/MusicPlayerDaemon/MPD/issues/720
This commit is contained in:
Max Kellermann 2020-01-27 21:33:37 +01:00
parent faf149d08e
commit 0b2444450f
2 changed files with 62 additions and 7 deletions
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1
NEWS
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@ -19,6 +19,7 @@ ver 0.22 (not yet released)
- mad: remove option "gapless", always do gapless
- sidplay: add option "default_genre"
- sidplay: map SID name field to "Album" tag
- vorbis, opus: improve seeking accuracy
* playlist
- flac: support reading CUE sheets from remote FLAC files
* filter

64
src/decoder/plugins/OggDecoder.cxx
View File

@ -80,12 +80,66 @@ OggDecoder::SeekGranulePos(ogg_int64_t where_granulepos)
{
assert(IsSeekable());
/* interpolate the file offset where we expect to find the
given granule position */
/* TODO: implement binary search */
offset_type offset(where_granulepos * input_stream.GetSize()
/ end_granulepos);
/* binary search: interpolate the file offset where we expect
to find the given granule position, and repeat until we're
close enough */
static const ogg_int64_t MARGIN_BEFORE = 44100 / 3;
static const ogg_int64_t MARGIN_AFTER = 44100 / 10;
offset_type min_offset = 0, max_offset = input_stream.GetSize();
ogg_int64_t min_granule = 0, max_granule = end_granulepos;
while (true) {
const offset_type delta_offset = max_offset - min_offset;
const ogg_int64_t delta_granule = max_granule - min_granule;
const ogg_int64_t relative_granule = where_granulepos - min_granule;
const offset_type offset = min_offset + relative_granule * delta_offset
/ delta_granule;
SeekByte(offset);
const auto new_granule = ReadGranulepos();
if (new_granule < 0)
/* no granulepos here, which shouldn't happen
- we can't improve, so stop */
return;
if (new_granule > where_granulepos + MARGIN_AFTER) {
if (new_granule > max_granule)
/* something went wrong */
return;
if (max_granule == new_granule)
/* break out of the infinite loop, we
can't get any closer */
break;
/* reduce the max bounds and interpolate again */
max_granule = new_granule;
max_offset = GetStartOffset();
} else if (new_granule + MARGIN_BEFORE < where_granulepos) {
if (new_granule < min_granule)
/* something went wrong */
return;
if (min_granule == new_granule)
/* break out of the infinite loop, we
can't get any closer */
break;
/* increase the min bounds and interpolate
again */
min_granule = new_granule;
min_offset = GetStartOffset();
} else {
break;
}
}
/* go back to the last page start so OggVisitor can start
visiting from here (we have consumed a few pages
already) */
SeekByte(GetStartOffset());
}