Efficiency improvements in OggExtractor
change from reading 4-bytes at a time to reading 2048-bytes at a time.
Rework backward search so that it no longer repeatedly scans the rest of
the data source as it searches further back; make the backwards scan a
true backwards scan
Bug: 263074833
Test: OggExtractor tests,
Test: playback of problematic ringtone
Merged-In: Ibec81305ca3cae37a990b7d223a10bb8d7864051
Change-Id: I828906d95d14f0ad612bafe6b19494dbd3a037df
diff --git a/media/extractors/ogg/OggExtractor.cpp b/media/extractors/ogg/OggExtractor.cpp
index eb2246d..11f93b5 100644
--- a/media/extractors/ogg/OggExtractor.cpp
+++ b/media/extractors/ogg/OggExtractor.cpp
@@ -34,6 +34,9 @@
#include <system/audio.h>
#include <utils/String8.h>
+#include <inttypes.h>
+#include <stdint.h>
+
extern "C" {
#include <Tremolo/codec_internal.h>
@@ -346,66 +349,118 @@
off64_t startOffset, off64_t *pageOffset) {
*pageOffset = startOffset;
- for (;;) {
- char signature[4];
- ssize_t n = mSource->readAt(*pageOffset, &signature, 4);
+ // balance between larger reads and reducing how much we over-read.
+ const int FIND_BUF_SIZE = 2048;
+ const int lenOggS = strlen("OggS");
+ while(1) {
- if (n < 4) {
+ // work with big buffers to amortize readAt() costs
+ char signatureBuffer[FIND_BUF_SIZE];
+ ssize_t n = mSource->readAt(*pageOffset, &signatureBuffer, sizeof(signatureBuffer));
+
+ if (n < lenOggS) {
*pageOffset = 0;
-
return (n < 0) ? n : (status_t)ERROR_END_OF_STREAM;
}
- if (!memcmp(signature, "OggS", 4)) {
- if (*pageOffset > startOffset) {
- ALOGV("skipped %lld bytes of junk to reach next frame",
- (long long)(*pageOffset - startOffset));
- }
-
- return OK;
- }
-
- // see how far ahead to skip; avoid some fruitless comparisons
- unsigned int i;
- for (i = 1; i < 4 ; i++) {
- if (signature[i] == 'O')
+ for(int i = 0; i < n - (lenOggS - 1) ; i++) {
+ // fast scan for 1st character in a signature
+ char *p = (char *)memchr(&signatureBuffer[i], 'O', n - (lenOggS - 1) - i);
+ if (p == NULL) {
+ // no signature start in the rest of this buffer.
break;
+ }
+ int jump = (p-&signatureBuffer[i]);
+ i += jump;
+ if (memcmp("OggS", &signatureBuffer[i], lenOggS) == 0) {
+ *pageOffset += i;
+ if (*pageOffset > startOffset) {
+ ALOGD("skipped %" PRIu64 " bytes of junk to reach next frame",
+ (*pageOffset - startOffset));
+ }
+ return OK;
+ }
}
- *pageOffset += i;
+
+ // on to next block. buffer didn't end with "OggS", but could end with "Ogg".
+ // overlap enough to detect this. n >= lenOggS, so this always advances.
+ *pageOffset += n - (lenOggS - 1);
}
+ return (status_t)ERROR_END_OF_STREAM;
}
// Given the offset of the "current" page, find the page immediately preceding
// it (if any) and return its granule position.
// To do this we back up from the "current" page's offset until we find any
// page preceding it and then scan forward to just before the current page.
+//
status_t MyOggExtractor::findPrevGranulePosition(
off64_t pageOffset, uint64_t *granulePos) {
*granulePos = 0;
- off64_t prevPageOffset = 0;
- off64_t prevGuess = pageOffset;
- for (;;) {
- if (prevGuess >= 5000) {
- prevGuess -= 5000;
+ const int FIND_BUF_SIZE = 2048;
+ const int lenOggS = strlen("OggS");
+
+ if (pageOffset == 0) {
+ ALOGV("no page before the first page");
+ return UNKNOWN_ERROR;
+ }
+
+ off64_t prevPageOffset = pageOffset;
+
+ // we start our search on the byte immediately in front of pageOffset
+ // which could mean "O" immediately before and "ggS" starting at pageOffset
+ //
+ // if there was an "OggS" at pageOffset, we'll have scanned a few extra bytes
+ // but if pageOffset was chosen by a seek operation, we don't know that it
+ // reflects the beginning of a page. By choosing to scan 3 possibly unneeded
+ // bytes at the start we cover both cases.
+ //
+ off64_t firstAfter = pageOffset + lenOggS - 1; // NOT within our buffer
+ off64_t nextOffset = pageOffset;
+
+ while(prevPageOffset == pageOffset) {
+ // work with big buffers to amortize readAt() costs
+ char signatureBuffer[FIND_BUF_SIZE];
+
+ ssize_t desired = sizeof(signatureBuffer);
+ if (firstAfter >= desired) {
+ nextOffset = firstAfter - desired;
} else {
- prevGuess = 0;
+ nextOffset = 0;
+ desired = firstAfter;
}
+ ssize_t n = mSource->readAt(nextOffset, &signatureBuffer, desired);
- ALOGV("backing up %lld bytes", (long long)(pageOffset - prevGuess));
-
- status_t err = findNextPage(prevGuess, &prevPageOffset);
- if (err == ERROR_END_OF_STREAM) {
- // We are at the last page and didn't back off enough;
- // back off 5000 bytes more and try again.
- continue;
- } else if (err != OK) {
- return err;
- }
-
- if (prevPageOffset < pageOffset || prevGuess == 0) {
+ if (n < lenOggS) {
+ ALOGD("short read, get out");
break;
}
+
+ // work backwards
+ // loop control ok for n >= 0
+ for(int i = n - lenOggS; i >= 0 ; i--) {
+ // fast scan for 1st character in the signature
+ char *p = (char *)memrchr(&signatureBuffer[0], 'O', i);
+ if (p == NULL) {
+ // no signature start in the rest of this buffer.
+ break;
+ }
+ i = (p-&signatureBuffer[0]);
+ // loop start chosen to ensure we will always have lenOggS bytes
+ if (memcmp("OggS", &signatureBuffer[i], lenOggS) == 0) {
+ prevPageOffset = nextOffset + i;
+ break;
+ }
+ }
+
+ // back up for next read; make sure we catch overlaps
+ if (nextOffset == 0) {
+ // can't back up any further
+ break;
+ }
+ // current buffer might start with "ggS", include those bytes in the next iteration
+ firstAfter = nextOffset + lenOggS - 1;
}
if (prevPageOffset == pageOffset) {
@@ -413,8 +468,8 @@
return UNKNOWN_ERROR;
}
- ALOGV("prevPageOffset at %lld, pageOffset at %lld",
- (long long)prevPageOffset, (long long)pageOffset);
+ ALOGV("prevPageOffset at %" PRIu64 ", pageOffset at %" PRIu64,
+ prevPageOffset, pageOffset);
uint8_t flag = 0;
for (;;) {
Page prevPage;
