1. Multi-Threading LAME MP3 Encoder
TECHNION - ISRAEL INSTITUTE OF TECHNOLOGY
Electrical
Engineering
Department
Software
Systems
Lab
Multi-Threading LAME MP3 Encoder
Performed by : Gilad Riachshtian
Copyright, 2004 © Gilad Raichshtain.

2. Talk Layout What is the L.A.M.E. Project ? Project Goal
MP3 Encoding & Hyper-Threading Overview
Multi-Threading strategies
Results & Remarks
Future Work

3. What is the L.A.M.E. Project?
An Open Source project
An Educational Tool used for learning about MP3 encoding
It’s goal is to improve
Psycho-acoustics quality
The speed of MP3 encoding
Lame is the most popular state of the art MP3 encoder/decoder used by today’s leading products.
FOR MORE INFO...

4. Project Goal Speeding up the encryption of an audio stream
Turning LAME into a Multi-Threaded (MT) engine
Be 1:1 bit compatible with the original version
Optimize specifically for SMT platforms (implementation on Intel’s P4 with Hyper-Threading Technology)

5. Thread Level Parallelism
Provides thread level parallelism on each processor
Resulting in
Increased use of processor execution resources
Higher processing throughput
Achieved by duplicating the architectural state on each processor, while sharing one set of processor execution resources

6. MP3 Encoding Overview Specifically in LAME
Break up the audio stream into frames (uniform chunks, typically ~1K)
Frame 1
Audio Stream
Frame 2
Frame 3
Frame 4
Read Frame
Psycho-Acoustic
Perceptual Model
Analysis Filterbank
MDCT
Quantization
Huffman Encoding
Bitstream Encode
Specifically in LAME

7. LAME MT – Intuitive approach
The intuitive approach:
Frame 1
Frame 2
Frame 3
Frame 4
Frame 5
Frame 6
Thread 1:
Thread 2:
An unbreakable dependence due to Huffman Encoding
This is actually Data Decomposition

8. LAME MT – Functional Decomposition
Frame 1
Frame 2
Frame 3
Frame 4
Frame 5
Frame 6
Floating Point Intensive
T1:
Psycho-Acoustic
Read Frame
Analysis Filterbank
MDCT
Quantization
Huffman Encoding
T2:
Integer Intensive

9. Results

10. Results due to Multi-Threading
SMT Platform
CBR / VBR
SMP Platform
Using Microsoft’s Compiler
22% / 32%
38% / 62%
Using Intel’s Compiler 8.1
20% / 29%
44% / 59%

11. Results using Intel’s Compiler 8.1
SMT Platform
CBR / VBR
SMP Platform
LAME Original Code 3.97a
21% / 19%
22% / 17%
LAME MT Code
19% / 17%
28% / 15%

12. Overall Performance Results
SMT Platform
CBR / VBR
SMP Platform
LAME MT code +
Using Intel’s Compiler 8.1
52% / 70%
78% / 109%

13. Remarks Architectural Issues Implement a PNI version for FFT
Pitfall found in version 3.93:
Memory access to two different pages with the same offset
~11% speedup achieved by fixing it
No longer relevant in later versions 
No major arch issues found in versions a
Implement a PNI version for FFT
No significant gain achieved
Overall ~40 blocks of code were change and are under #ifdef

14. Future work

15. Future Work Splitting the encoding process into more than two steps
Reading frames in parallel

16. That's all Folks