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Decoding the residual in FLAC subframes is by far the most I/O-heavy operation in FLAC decoding, as the residual data makes up the majority of subframe data in LPC subframes. As the residual consists of many Rice-encoded numbers with different bit sizes for differently large numbers, the residual decoder frequently reads only one or two bytes at a time. As we use a normal FileInputStream, that directly translates to many calls to the read() syscall. We can see that the I/O overhead while FLAC decoding is quite large, and much time is spent in the read() syscall's kernel code. This is optimized by using a Buffered<FileInputStream> instead, leading to 4K blocks being read at once and a large reduction in I/O overhead. Benchmarking with the new abench utility gives a 15-20% speedup on identical files, usually pushing FLAC decoding to 10-15x realtime speed on common sample rates. |
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| .. | ||
| Buffer.cpp | ||
| Buffer.h | ||
| ClientConnection.cpp | ||
| ClientConnection.h | ||
| CMakeLists.txt | ||
| FlacLoader.cpp | ||
| FlacLoader.h | ||
| FlacTypes.h | ||
| Loader.cpp | ||
| Loader.h | ||
| Sample.h | ||
| WavLoader.cpp | ||
| WavLoader.h | ||
| WavWriter.cpp | ||
| WavWriter.h | ||