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README.md

ESP32-S3 Opus Encode Benchmark

Benchmarks Opus encoding performance across a matrix of settings using two 30-second audio clips. Tests speech encoding (SILK codec, low bitrates) and music encoding (CELT codec, high bitrates), reporting per-frame timing statistics and actual vs target bitrate.

Features

  • Two embedded 30-second test audio clips (public domain):
    • SPEECH (SILK): 16kHz mono, tests low-bitrate encoding (10-32 kbit/s)
    • MUSIC (CELT): 48kHz stereo, tests high-bitrate encoding (64-192 kbit/s)
  • Full test matrix: complexity levels (0, 2, 5, 8, 10) x application modes (VOIP, AUDIO) x bitrates
  • Per-frame encoding timing with statistical analysis (min/max/avg/stddev)
  • Only encodes are timed (decode time excluded from measurements)
  • Actual vs target bitrate comparison
  • Auto-skip: stops test series when encoding becomes slower than real-time
  • Pre-configured for maximum performance (240MHz, PSRAM, fixed-point)

Test Matrix

Speech (40 configurations)

Mode Complexity Bitrates
VOIP 0, 2, 5, 8, 10 10k, 16k, 24k, 32k
AUDIO 0, 2, 5, 8, 10 10k, 16k, 24k, 32k

Music (20 configurations)

Mode Complexity Bitrates
AUDIO 0, 2, 5, 8, 10 64k, 96k, 128k, 192k

Building and Flashing

Prerequisites

  • PlatformIO (recommended) OR ESP-IDF v5.0 or later
  • ESP32-S3 development board with PSRAM

Option 1: PlatformIO (Recommended)

PlatformIO provides a simplified build process with automatic dependency management.

cd examples/encode_benchmark

# Build the project
pio run

# Upload and monitor
pio run -t upload -t monitor

The PlatformIO configuration uses the parent microOpus repository as a component, so no additional setup is required.

Option 2: Native ESP-IDF

cd examples/encode_benchmark
idf.py set-target esp32s3
idf.py build
idf.py flash monitor

Configuration Options

PlatformIO

The default configuration is optimized for maximum performance. To customize:

  1. Edit sdkconfig.defaults to change Opus-specific settings
  2. Use pio run -t menuconfig for full ESP-IDF configuration

Native ESP-IDF

idf.py menuconfig

Navigate to Component config → Opus Audio Codec to adjust:

  • Memory allocation mode (THREADSAFE_PSEUDOSTACK, NONTHREADSAFE_PSEUDOSTACK, USE_ALLOCA)
  • Floating-point vs fixed-point implementation
  • Memory preferences (PSRAM vs internal RAM for state/pseudostack)
  • Pseudostack size

Expected Output

Each iteration runs through all encoder configurations for both audio types:

I (1019) ENCODE_BENCH: === ESP32-S3 Opus Encode Benchmark ===
I (1019) ENCODE_BENCH: Audio sources:
I (1029) ENCODE_BENCH:   SPEECH (SILK): 38196 bytes, 16 kHz, 1 channel
I (1029) ENCODE_BENCH:   MUSIC (CELT): 497933 bytes, 48 kHz, 2 channels
I (1039) ENCODE_BENCH: Processing: decode packet -> encode packet (timing encode only)
I (1049) ENCODE_BENCH: Test matrix: 40 speech configs + 20 music configs = 60 total
I (1049) ENCODE_BENCH: Free heap: 17070164 bytes
I (1059) ENCODE_BENCH: Free PSRAM: 16774624 bytes
I (1059) ENCODE_BENCH: Free Internal: 295540 bytes

I (1069) ENCODE_BENCH: ========== Iteration 1 ==========

I (1079) ENCODE_BENCH: === SPEECH Encoding Tests (40 configurations) ===

I (1079) ENCODE_BENCH: --- SPEECH: VOIP, complexity=0, bitrate=10000 ---
I (9149) ENCODE_BENCH: Frame (us): min=3370 max=4684 avg=4082.5 sd=463.9 (n=1500)
I (9149) ENCODE_BENCH: Total: 6123 ms (30.0s audio), RTF: 0.204 (4.9x real-time)
I (9149) ENCODE_BENCH: Encoded: 34542 bytes (9211 bps actual, target 10000 bps)

...

I (589889) ENCODE_BENCH: --- SPEECH: AUDIO, complexity=10, bitrate=32000 ---
I (602159) ENCODE_BENCH: Frame (us): min=4251 max=8040 avg=6725.8 sd=594.7 (n=1500)
I (602159) ENCODE_BENCH: Total: 10088 ms (30.0s audio), RTF: 0.336 (3.0x real-time)
I (602159) ENCODE_BENCH: Encoded: 121566 bytes (32418 bps actual, target 32000 bps)

I (602169) ENCODE_BENCH: === MUSIC Encoding Tests (20 configurations) ===

I (602179) ENCODE_BENCH: --- MUSIC: AUDIO, complexity=0, bitrate=64000 ---
I (618689) ENCODE_BENCH: Frame (us): min=5530 max=6602 avg=6330.5 sd=98.6 (n=1500)
I (618689) ENCODE_BENCH: Total: 9495 ms (30.0s audio), RTF: 0.317 (3.2x real-time)
I (618699) ENCODE_BENCH: Encoded: 241654 bytes (64441 bps actual, target 64000 bps)

...

I (1041739) ENCODE_BENCH: --- MUSIC: AUDIO, complexity=10, bitrate=192000 ---
I (1041739) ENCODE_BENCH: Frame (us): min=8468 max=16662 avg=12890.2 sd=1985.3 (n=1500)
I (1041749) ENCODE_BENCH: Total: 19335 ms (30.0s audio), RTF: 0.645 (1.6x real-time)
I (1041749) ENCODE_BENCH: Encoded: 721980 bytes (192528 bps actual, target 192000 bps)

I (1041759) ENCODE_BENCH: === Iteration 1 Summary ===
I (1041759) ENCODE_BENCH: All encodes successful: YES
I (1041769) ENCODE_BENCH: Free heap: 16949064 bytes

Output Fields

  • Frame (us): Per-frame encode time statistics (min/max/avg/sd in microseconds, n = frame count)
  • Total: Wall-clock time spent encoding all frames
  • RTF: Real-Time Factor (encode_time / audio_duration). RTF < 1 means faster than real-time
  • Nx real-time: How many times faster than real-time encoding (1/RTF)
  • Encoded: Compressed size and actual bitrate vs target bitrate

Auto-Skip Behavior

When encoding becomes slower than real-time (RTF > 1.0), the benchmark skips remaining configurations in that audio type since higher complexity/bitrate settings will be even slower:

W (95000) ENCODE_BENCH: RTF > 1.0, skipping remaining MUSIC tests (higher settings will be slower)

Benchmark Results (Fixed-Point)

Results from ESP32-S3 at 240MHz using fixed-point arithmetic (CONFIG_OPUS_FLOATING_POINT=n). Fixed-point encoding is significantly faster than floating-point on ESP32-S3, especially for SILK at higher complexity levels where floating-point fails to encode in real-time.

Values show real-time multiplier with RTF in parentheses.

Speech Encoding (16kHz mono)

VOIP Mode

Complexity 10 kbit/s 16 kbit/s 24 kbit/s 32 kbit/s
0 4.9x (0.20) 3.9x (0.26) 3.8x (0.26) 3.8x (0.26)
2 2.9x (0.34) 2.9x (0.34) 2.9x (0.34) 2.9x (0.35)
5 2.1x (0.48) 2.1x (0.49) 2.1x (0.49) 2.0x (0.49)
8 1.5x (0.68) 1.5x (0.68) 1.5x (0.68) 1.5x (0.68)
10 1.5x (0.68) 1.5x (0.68) 1.5x (0.68) 1.5x (0.68)

AUDIO Mode

Complexity 10 kbit/s 16 kbit/s 24 kbit/s 32 kbit/s
0 5.0x (0.20) 3.9x (0.26) 5.5x (0.18) 5.4x (0.18)
2 3.0x (0.34) 2.9x (0.34) 4.6x (0.22) 4.6x (0.22)
5 2.1x (0.48) 2.1x (0.48) 3.0x (0.33) 3.0x (0.33)
8 1.5x (0.68) 1.5x (0.67) 3.0x (0.34) 3.0x (0.34)
10 1.5x (0.68) 1.5x (0.67) 3.0x (0.34) 3.0x (0.34)

Bold = CELT/SILK hybrid (faster than SILK at same bitrate)

Music Encoding (48kHz stereo, AUDIO mode)

Complexity 64 kbit/s 96 kbit/s 128 kbit/s 192 kbit/s
0 3.2x (0.32) 3.0x (0.34) 2.8x (0.35) 2.6x (0.38)
2 2.6x (0.38) 2.5x (0.41) 2.4x (0.42) 2.3x (0.44)
5 2.0x (0.51) 1.9x (0.53) 1.8x (0.55) 1.8x (0.57)
8 1.8x (0.54) 1.7x (0.59) 1.6x (0.62) 1.6x (0.65)
10 1.8x (0.54) 1.7x (0.59) 1.6x (0.62) 1.6x (0.65)

Key Observations

Finding Details
Complexity 8 = 10 No performance difference between complexity 8 and 10
CELT faster than SILK At 24+ kbit/s in AUDIO mode, encoder switches to CELT (~2x faster)
All configs real-time capable Worst case 1.5x real-time (complexity 8/10 VOIP speech)
Bitrate effect (SILK) Minimal impact on encode time
Bitrate effect (CELT) Higher bitrates slightly slower (more data to process)

Summary by Codec

Codec Best Case Worst Case Notes
SILK (speech) 4.9x @ c=0 1.5x @ c=8+ Bitrate has little effect on speed
CELT (speech) 5.5x @ c=0 3.0x @ c=8+ ~2x faster than SILK at same complexity
CELT (music) 3.2x @ c=0 1.6x @ c=8+ Stereo 48kHz more demanding than mono 16kHz

Benchmark Results (Floating-Point)

Results with CONFIG_OPUS_FLOATING_POINT=y for comparison. Floating-point is significantly slower for SILK encoding.

Speech Encoding (16kHz mono) - Floating-Point

Mode Complexity 10 kbit/s 16 kbit/s Higher
VOIP 0 1.1x (0.87) 0.7x (1.53) skipped
AUDIO 0 1.1x (0.87) 0.7x (1.53) skipped

Bold = Slower than real-time (RTF > 1.0). Higher complexity levels were not tested because complexity 0 already fails at 16 kbit/s.

Music Encoding (48kHz stereo, AUDIO mode) - Floating-Point

Complexity 64 kbit/s 96 kbit/s 128 kbit/s 192 kbit/s
0 2.9x (0.34) 2.7x (0.37) 2.5x (0.40) 2.2x (0.46)
2 2.5x (0.41) 2.3x (0.44) 2.1x (0.47) 1.9x (0.52)
5 2.0x (0.49) 1.9x (0.52) 1.8x (0.55) 1.7x (0.61)
8 1.4x (0.73) 1.3x (0.79) 1.2x (0.84) 1.1x (0.91)
10 1.4x (0.73) 1.3x (0.79) 1.2x (0.84) 1.1x (0.91)

Fixed-Point vs Floating-Point Comparison

Codec Fixed-Point Floating-Point Speedup
SILK (c=0, 10k) 4.9x real-time 1.1x real-time 4x faster
SILK (c=0, 16k) 3.9x real-time 0.7x (fails) 6x faster
CELT music (c=0, 64k) 3.2x real-time 2.9x real-time 1.1x faster
CELT music (c=8, 192k) 1.6x real-time 1.1x real-time 1.5x faster

Recommendation: Use fixed-point (CONFIG_OPUS_FLOATING_POINT=n) for encoding on ESP32-S3. SILK encoding with floating-point is not viable for real-time applications.

Performance Characteristics

Encoder Complexity

Opus complexity ranges from 0 (fastest) to 10 (best quality):

Complexity Trade-off
0-2 Fastest encoding, lower quality
5 Balanced (default in most applications)
8-10 Best quality, slowest encoding

Higher complexity uses more CPU cycles for analysis and psychoacoustic modeling. Note that complexity 8 and 10 show identical performance on ESP32-S3.

Application Mode

  • VOIP: Optimized for speech, prefers SILK codec even at higher bitrates
  • AUDIO: Optimized for music, prefers CELT codec, uses SILK only at very low bitrates

Bitrate Impact

Higher bitrates generally:

  • Increase encoding time (more data to process)
  • Improve audio quality
  • Result in larger compressed output

Configuration

The default configuration uses 240MHz, fixed-point, THREADSAFE_PSEUDOSTACK, and pseudostack in PSRAM.

Key settings in sdkconfig.defaults:

# Fixed-point (currently configured, can change to floating-point)
CONFIG_OPUS_FLOATING_POINT=n

Memory Usage

Type Size Notes
Flash ~640KB 100KB code + 498KB music + 38KB speech
Pseudostack 120KB Shared between encoder and decoder

Troubleshooting

Problem Solution
Watchdog timeout Already disabled in default config
Stack overflow Increase CONFIG_ESP_MAIN_TASK_STACK_SIZE
Allocation failures Check PSRAM is enabled, reduce pseudostack size, or set state to prefer PSRAM
All tests skip RTF > 1.0 on first test; consider lowering complexity or switching to floating-point

Technical Details

Processing Flow: For each encoder configuration, the benchmark:

  1. Decodes the embedded Opus file packet by packet using OggOpusDecoder
  2. Accumulates PCM samples until a full 20ms frame is ready
  3. Encodes the frame using the raw Opus encoder API (opus_encode)
  4. Times only the encode step (decode time is excluded)
  5. Reports statistics after processing all audio

Music Audio (CELT): Beethoven Symphony No. 3 "Eroica", Op. 55, Movement I, 30s extract.

  • Performer: Czech National Symphony Orchestra
  • Source: Musopen Collection on Archive.org
  • License: Public Domain
  • Format: Ogg Opus 48kHz stereo ~128kbit/s VBR (CELT codec)

Speech Audio (SILK): The Art of War, Chapters 1-2, 30s extract.

  • Author: Sun Tzu
  • Reader: Moira Fogarty (October 2006)
  • Source: LibriVox on Archive.org
  • License: Public Domain
  • Format: Ogg Opus 16kHz mono ~10kbit/s (SILK codec)

Timing: Uses esp_timer_get_time() for microsecond precision. Only measures opus_encode() calls.