ref: 4dcf9b0d60aea983bd40995a444109c4ddf2b7d3
parent: 99c3c5e98a375c00478311c4d986ed2471d5d949
author: Timothy B. Terriberry <tterribe@xiph.org>
date: Mon Nov 12 11:34:43 EST 2012
Add op_get_last_page() for calculating duration. Using op_get_prev_page_serial() meant if there were valid pages from another stream, we would re-scan them all repeatedly until we managed to back up, a page at a time, to a chunk with a page from the preferred stream with a valid granule position. Breaking this case into its own function means we can guarantee we only scan each page once, and that we can stop as soon as we hit a page from a different link (in the unlikely event that the stream has no pages with valid timestamps).
--- a/src/opusfile.c
+++ b/src/opusfile.c
@@ -262,9 +262,11 @@
/*We use this to remember the pages we found while enumerating the links of a
chained stream.
- We only need to know the starting and ending byte offsets and the serial
- number, so we can tell if the page belonged to the current chain or not,
- and where to bisect.*/
+ We keep track of the starting and ending offsets, as well as the point we
+ started searching from, so we know where to bisect.
+ We also keep the serial number, so we can tell if the page belonged to the
+ current link or not, as well as the granule position, to aid in estimating
+ the start of the link.*/
struct OpusSeekRecord{/*The earliest byte we know of such that reading forward from it causes
capture to be regained at this page.*/
@@ -286,16 +288,29 @@
This search prefers pages of the specified serial number.
If a page of the specified serial number is spotted during the
seek-back-and-read-forward, it will return the info of last page of the
- matching serial number, instead of the very last page.
+ matching serial number, instead of the very last page, unless the very last
+ page belongs to a different link than preferred serial number.
If no page of the specified serial number is seen, it will return the info of
- the last page and update *_serialno.
+ the last page.
+ [out] _sr: Returns information about the page that was found on success.
+ _offset: The _offset before which to find a page.
+ Any page returned will consist of data entirely before _offset.
+ _serialno: The preferred serial number.
+ If a page with this serial number is found, it will be returned
+ even if another page in the same link is found closer to
+ _offset.
+ This is purely opportunistic: there is no guarantee such a page
+ will be found if it exists.
+ _serialnos: The list of serial numbers in the link that contains the
+ preferred serial number.
+ _nserialnos: The number of serial numbers in the current link.
Return: 0 on success, or a negative value on failure.
OP_EREAD: Failed to read more data (error or EOF).
OP_EBADLINK: We couldn't find a page even after seeking back to the
start of the stream.*/
-static int op_get_prev_page_serial(OggOpusFile *_of,
- OpusSeekRecord *_sr,opus_int32 *_chunk_size,opus_int64 _offset,
- ogg_uint32_t _serialno,const ogg_uint32_t *_serialnos,int _nserialnos){+static int op_get_prev_page_serial(OggOpusFile *_of,OpusSeekRecord *_sr,
+ opus_int64 _offset,ogg_uint32_t _serialno,
+ const ogg_uint32_t *_serialnos,int _nserialnos){OpusSeekRecord preferred_sr;
ogg_page og;
opus_int64 begin;
@@ -306,7 +321,7 @@
original_end=end=begin=_offset;
preferred_found=0;
_offset=-1;
- chunk_size=_chunk_size==NULL?OP_CHUNK_SIZE:*_chunk_size;
+ chunk_size=OP_CHUNK_SIZE;
do{opus_int64 search_start;
int ret;
@@ -356,11 +371,95 @@
end=OP_MIN(begin+OP_PAGE_SIZE_MAX-1,original_end);
}
while(_offset<0);
- if(_chunk_size!=NULL)*_chunk_size=chunk_size;
if(preferred_found)*_sr=*&preferred_sr;
return 0;
}
+/*Find the last page beginning before _offset with the given serial number and
+ a valid granule position.
+ Unlike the above search, this continues until it finds such a page, but does
+ not stray outside the current link.
+ We could implement it (inefficiently) by calling op_get_prev_page_serial()
+ repeatedly until it returned a page that had both our preferred serial
+ number and a valid granule position, but doing it with a separate function
+ allows us to avoid repeatedly re-scanning valid pages from other streams as
+ we seek-back-and-read-forward.
+ [out] _gp: Returns the granule position of the page that was found on
+ success.
+ _offset: The _offset before which to find a page.
+ Any page returned will consist of data entirely before _offset.
+ _serialno: The target serial number.
+ _serialnos: The list of serial numbers in the link that contains the
+ preferred serial number.
+ _nserialnos: The number of serial numbers in the current link.
+ Return: The offset of the page on success, or a negative value on failure.
+ OP_EREAD: Failed to read more data (error or EOF).
+ OP_EBADLINK: We couldn't find a page even after seeking back past the
+ beginning of the link.*/
+static opus_int64 op_get_last_page(OggOpusFile *_of,ogg_int64_t *_gp,
+ opus_int64 _offset,ogg_uint32_t _serialno,
+ const ogg_uint32_t *_serialnos,int _nserialnos){+ ogg_page og;
+ ogg_int64_t gp;
+ opus_int64 begin;
+ opus_int64 end;
+ opus_int64 original_end;
+ opus_int32 chunk_size;
+ /*The target serial number must belong to the current link.*/
+ OP_ASSERT(op_lookup_serialno(_serialno,_serialnos,_nserialnos));
+ original_end=end=begin=_offset;
+ _offset=-1;
+ chunk_size=OP_CHUNK_SIZE;
+ do{+ int left_link;
+ int ret;
+ OP_ASSERT(chunk_size>=OP_PAGE_SIZE_MAX);
+ begin=OP_MAX(begin-chunk_size,0);
+ ret=op_seek_helper(_of,begin);
+ if(OP_UNLIKELY(ret<0))return ret;
+ left_link=0;
+ while(_of->offset<end){+ opus_int64 llret;
+ ogg_uint32_t serialno;
+ llret=op_get_next_page(_of,&og,end);
+ if(OP_UNLIKELY(llret<OP_FALSE))return (int)llret;
+ else if(llret==OP_FALSE)break;
+ serialno=ogg_page_serialno(&og);
+ if(serialno==_serialno){+ ogg_int64_t page_gp;
+ /*The page is from the right stream...*/
+ page_gp=ogg_page_granulepos(&og);
+ if(page_gp!=-1){+ /*And has a valid granule position.
+ Let's remember it.*/
+ _offset=llret;
+ gp=page_gp;
+ }
+ }
+ else if(OP_UNLIKELY(!op_lookup_serialno(serialno,
+ _serialnos,_nserialnos))){+ /*We fell off the start of the link, which means we don't need to keep
+ seeking any farther back.*/
+ left_link=1;
+ }
+ }
+ /*We started from at or before the beginning of the link and found nothing.
+ This should be impossible unless the contents of the source changed out
+ from under us after we read from it.*/
+ if((OP_UNLIKELY(left_link)||OP_UNLIKELY(!begin))&&OP_UNLIKELY(_offset<0)){+ return OP_EBADLINK;
+ }
+ /*Bump up the chunk size.
+ This is mildly helpful when seeks are very expensive (http).*/
+ chunk_size=OP_MIN(2*chunk_size,OP_CHUNK_SIZE_MAX);
+ /*Avoid quadratic complexity if we hit an invalid patch of the file.*/
+ end=OP_MIN(begin+OP_PAGE_SIZE_MAX-1,original_end);
+ }
+ while(_offset<0);
+ *_gp=gp;
+ return _offset;
+}
+
/*Uses the local ogg_stream storage in _of.
This is important for non-streaming input sources.*/
static int op_fetch_headers_impl(OggOpusFile *_of,OpusHead *_head,
@@ -858,30 +957,21 @@
const ogg_uint32_t *_serialnos,int _nserialnos,OggOpusLink *_link,
opus_int64 _offset,ogg_uint32_t _end_serialno,ogg_int64_t _end_gp,
ogg_int64_t *_total_duration){- OpusSeekRecord sr;
- ogg_int64_t total_duration;
- ogg_int64_t duration;
- ogg_uint32_t cur_serialno;
- opus_int32 chunk_size;
+ ogg_int64_t total_duration;
+ ogg_int64_t duration;
+ ogg_uint32_t cur_serialno;
/*For the time being, fetch end PCM offset the simple way.*/
cur_serialno=_link->serialno;
- sr.offset=_offset;
- sr.serialno=_end_serialno;
- sr.gp=_end_gp;
- /*Keep track of the growing chunk size to better handle being multiplexed
- with another high-bitrate stream.*/
- chunk_size=OP_CHUNK_SIZE;
- while(sr.gp==-1||sr.serialno!=cur_serialno){- int ret;
- ret=op_get_prev_page_serial(_of,&sr,&chunk_size,sr.offset,
+ if(_end_serialno!=cur_serialno||_end_gp==-1){+ _offset=op_get_last_page(_of,&_end_gp,_offset,
cur_serialno,_serialnos,_nserialnos);
- if(OP_UNLIKELY(ret<0))return ret;
+ if(OP_UNLIKELY(_offset<0))return (int)_offset;
}
/*This implementation requires that the difference between the first and last
granule positions in each link be representable in a signed, 64-bit
number, and that each link also have at least as many samples as the
pre-skip requires.*/
- if(OP_UNLIKELY(op_granpos_diff(&duration,sr.gp,_link->pcm_start)<0)
+ if(OP_UNLIKELY(op_granpos_diff(&duration,_end_gp,_link->pcm_start)<0)
||OP_UNLIKELY(duration<_link->head.pre_skip)){return OP_EBADTIMESTAMP;
}
@@ -891,8 +981,8 @@
total_duration=*_total_duration;
if(OP_UNLIKELY(OP_INT64_MAX-duration<total_duration))return OP_EBADTIMESTAMP;
*_total_duration=total_duration+duration;
- _link->pcm_end=sr.gp;
- _link->end_offset=sr.offset;
+ _link->pcm_end=_end_gp;
+ _link->end_offset=_offset;
return 0;
}
@@ -1257,7 +1347,7 @@
/*Get the offset of the last page of the physical bitstream, or, if we're
lucky, the last Opus page of the first link, as most Ogg Opus files will
contain a single logical bitstream.*/
- ret=op_get_prev_page_serial(_of,sr,NULL,_of->end,
+ ret=op_get_prev_page_serial(_of,sr,_of->end,
_of->links[0].serialno,_of->serialnos,_of->nserialnos);
if(OP_UNLIKELY(ret<0))return ret;
/*If there's any trailing junk, forget about it.*/