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Fix FLAC interactions with PBA 'remaining capacity'

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The comment sounds like it is worried the next header won't fit after
`limit` and before the end of `data`, but the code was previously only
checking the space between `position` and `limit`. This led to some
unnecessary copies.

Running the Robolectric `FlacExtractorTest.sample()` test in only the
'partial reads' and I/O errors case (worst case for this bug) results
in 57271 copies without this fix, and 19 copies with it.

Sample of the first 10 copies before this fix, showing a copy is made
for every byte read from the input:

```
W/ibaker: Making a copy. input.position=8881, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8882, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8883, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8884, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8885, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8886, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8887, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8888, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8889, data.length=32768, pos=1, lim=1
W/ibaker: Making a copy. input.position=8890, data.length=32768, pos=1, lim=1
```

And the first 10 copies after the fix:

```
W/ibaker: Making a copy. input.position=41648, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=74401, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=107154, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=139907, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=172660, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=41648, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=74401, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=107154, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=139907, data.length=32768, pos=32753, lim=32768
W/ibaker: Making a copy. input.position=172660, data.length=32768, pos=32753, lim=32768
```

PiperOrigin-RevId: 738341007
(cherry picked from commit 71ff9c661cccaf2d0c0f9c67008911b4ec5a4397)
This commit is contained in:
ibaker 2025-03-19 04:24:49 -07:00 committed by tonihei
parent 673da97fde
commit 75e28d82e3
1 changed files with 7 additions and 3 deletions
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10
libraries/extractor/src/main/java/androidx/media3/extractor/flac/FlacExtractor.java
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@ -310,9 +310,13 @@ public final class FlacExtractor implements Extractor {
currentFrameFirstSampleNumber = nextFrameFirstSampleNumber;
}
if (buffer.bytesLeft() < FlacConstants.MAX_FRAME_HEADER_SIZE) {
// The next frame header may not fit in the rest of the buffer, so put the trailing bytes at
// the start of the buffer, and reset the position and limit.
int remainingBufferCapacity = buffer.getData().length - buffer.limit();
if (buffer.bytesLeft() < FlacConstants.MAX_FRAME_HEADER_SIZE
&& remainingBufferCapacity < FlacConstants.MAX_FRAME_HEADER_SIZE) {
// We're running out of bytes to read before buffer.limit, and the next frame header may not
// fit in the rest of buffer.data beyond buffer.limit, so we move the bytes between
// buffer.position and buffer.limit to the start of buffer.data, and reset the position and
// limit.
int bytesLeft = buffer.bytesLeft();
System.arraycopy(
buffer.getData(), buffer.getPosition(), buffer.getData(), /* destPos= */ 0, bytesLeft);