Compiling Kaldi to WebAssembly 

Overview

• There is an older guide for this that compiled Kaldi with CLAPACK (not properly tested) and Netlib's Reference BLAS, which exists solely for implementers of the BLAS standard to verify the correctness of their own implementation, and thus, not optimized for performance.

• This newer guide compile Kaldi using OpenBLAS, a high-performance, optimized, actively maintained BLAS library officially supported by Kaldi. It also includes both BLAS and LAPACK. This was profiled to speed up Kaldi by around 20% compared to the build with Netlib's Reference BLAS and CLAPACK.

• This guide compiles Kaldi's "online decoding" target online2 More info: https://kaldi-asr.org/doc/online_decoding.html

• Guide version will be updated to follow Emscripten/OpenFST/OpenBLAS version change

Current versions

• Emscripten: 3.1.69
• OpenFST: 1.8.4
• OpenBLAS: 0.3.28
• Kaldi: ???

Step 1: Prepare

• Execute all commands in one terminal
• Make a directory and change into it before starting
• Compilation optimization level is -O3 by default througout this guide

# Our build root, exported so that we can refer to it in this terminal
export ROOT="$PWD"

# Clone this repository
git clone --depth 1 https://github.com/msqr1/kaldi-wasm2 "$ROOT"

# Enter that directory
cd "$ROOT"

• Optional: WASM-specific compilation flags that can boost performance, selected by me with careful condsideration on browser support:
  • Chrome ≥ 75 (2019)
  • Firefox ≥ 79 (2020)
  • Safari ≥ 15 (2021)
  • Edge ≥ 79 (2020)
• Wasm features support table
• Wasm flags list

export WAFLAGS="-mbulk-memory -mnontrapping-fptoint -mmutable-globals -msign-ext"

Step 2: Emscripten

• As of writing, Emscripten 3.1.6x is known to work
• Reference this guide to setup Emscripten, the WASM compiler

# Get EMSDK
git clone https://github.com/emscripten-core/emsdk.git

# Enter that directory
cd emsdk

# Install Emscripten
./emsdk install 3.1.69

# Activate Emcripten
./emsdk activate 3.1.69

# Add Emscripten tools to current terminal
source ./emsdk_env.sh

Step 3: OpenFST

# Go to build root
cd "$ROOT"

# Get OpenFST
wget https://www.openfst.org/twiki/pub/FST/FstDownload/openfst-1.8.4.tar.gz -O openfst.tgz

# Decompress
mkdir openfst
tar -xzf openfst.tgz -C openfst --strip-component 1

# Enter that directory
cd openfst

# OpenFST bug fixes
# Invalid assignment
patch -i "$ROOT"/patches/openfst/fst.h.patch ./src/include/fst/fst.h

# Undefined member variable
patch -i "$ROOT"/patches/openfst/bi-table.h.patch ./src/include/fst/bi-table.h

# Configuring static OpenFST with Ngram fsts
CXXFLAGS="$WAFLAGS -O3 -fno-rtti" emconfigure ./configure --prefix="$ROOT/openfst-build" --enable-static --disable-shared --enable-ngram-fsts --disable-bin

# Compile and install into prefix
emmake make -j$(nproc) install > /dev/null

Step 4: OpenBLAS

• The most crucial step of the build, some hacks are required for this to work

# Go to build root
cd "$ROOT"

# Get OpenBLAS
git clone -b v0.3.28 --depth=1 https://github.com/OpenMathLib/OpenBLAS openblas

# Enter that directory
cd openblas

# OpenBLAS hacks: remove march'es, fPIC, etc.
patch -i "$ROOT"/patches/openblas/Makefile.riscv64.patch Makefile.riscv64
patch -i "$ROOT"/patches/openblas/Makefile.prebuild.patch Makefile.prebuild
patch -i "$ROOT"/patches/openblas/Makefile.system.patch Makefile.system

# Make single-threaded static OpenBLAS with just single and double precision
# Change HOSTCC to the C compiler on your machine. Mine is gcc-12 from Debian 12
CC=emcc HOSTCC=gcc-12 TARGET=RISCV64_GENERIC USE_THREAD=0 NO_SHARED=1 BINARY=32 BUILD_SINGLE=1 BUILD_DOUBLE=1 BUILD_BFLOAT16=0 BUILD_COMPLEX16=0 BUILD_COMPLEX=0 CFLAGS="$WAFLAGS -fno-exceptions -fno-rtti" make -j$(nproc) > /dev/null

# Install into prefix
PREFIX="$ROOT/openblas-build" NO_SHARED=1 make install

Step 5: Kaldi

# Go to build root
cd "$ROOT"

# Get Kaldi
git clone --depth 1 https://github.com/msqr1/new-kaldi-wasm

# Enter Kaldi source
cd kaldi/src

# Configuring static Kaldi with static installed dependencies
CXXFLAGS="$WAFLAGS -UHAVE_EXECINFO_H -g0 -O3 -msimd128" emconfigure ./configure --use-cuda=no --with-cudadecoder=no --static --static-math --static-fst --fst-root="$ROOT/openfst-build" --fst-version='1.8.4' --openblas-root="$ROOT/openblas-build" --host=WASM

# Compile our target
make -j$(nproc) online2 > /dev/null

Step 6: Clean up

# Go to build root
cd "$ROOT"

# Clean up
rm -rf openfst.tgz openfst openblas

Full command

export ROOT="$PWD"
git clone --depth 1 https://github.com/msqr1/kaldi-wasm2 "$ROOT"
cd "$ROOT"
git clone --depth 1 https://github.com/emscripten-core/emsdk.git
cd emsdk
./emsdk install 3.1.69
./emsdk activate 3.1.69
source emsdk_env.sh
cd "$ROOT"
export WAFLAGS="-mbulk-memory -mnontrapping-fptoint -mmutable-globals -msign-ext"
wget https://www.openfst.org/twiki/pub/FST/FstDownload/openfst-1.8.4.tar.gz -O openfst.tgz
mkdir openfst
tar -xzf openfst.tgz -C openfst --strip-component 1
cd openfst
CXXFLAGS="$WAFLAGS -O3 -fno-rtti" emconfigure ./configure --prefix="$ROOT/openfst-build" --enable-static --disable-shared --enable-ngram-fsts --disable-bin
emmake make -j$(nproc) install > /dev/null
cd "$ROOT"
git clone -b v0.3.28 --depth=1 https://github.com/OpenMathLib/OpenBLAS openblas
cd openblas
patch -i "$ROOT"/patches/openblas/Makefile.riscv64.patch Makefile.riscv64
patch -i "$ROOT"/patches/openblas/Makefile.prebuild.patch Makefile.prebuild
patch -i "$ROOT"/patches/openblas/Makefile.system.patch Makefile.system
CC=emcc HOSTCC=gcc-12 TARGET=RISCV64_GENERIC USE_THREAD=0 NO_SHARED=1 BINARY=32 BUILD_SINGLE=1 BUILD_DOUBLE=1 BUILD_BFLOAT16=0 BUILD_COMPLEX16=0 BUILD_COMPLEX=0 CFLAGS="$WAFLAGS -fno-exceptions -fno-rtti" make -j$(nproc) > /dev/null
PREFIX="$ROOT/openblas-build" NO_SHARED=1 make install
cd "$ROOT"
git clone --depth 1 https://github.com/msqr1/new-kaldi-wasm kaldi
cd kaldi/src
CXXFLAGS="$WAFLAGS -UHAVE_EXECINFO_H -g0 -O3 -msimd128" emconfigure ./configure --use-cuda=no --with-cudadecoder=no --static --static-math --static-fst --fst-root="$ROOT/openfst-build" --fst-version='1.8.4' --openblas-root="$ROOT/openblas-build" --host=WASM
make -j$(nproc) online2 > /dev/null
cd "$ROOT"
rm -rf openfst.tgz openfst openblas

Linking and running example

• We're going to run nnet2/am-nnet-test.cc

# Compiler flags
export CXXFLAGS="
-DOPENFST_VER=10803
-I$ROOT/kaldi/src
-I$ROOT/openfst-build/include
-I$ROOT/openblas-build/include"

# Linker flags
export LDFLAGS="
-L$ROOT/kaldi/src
-l:online2/kaldi-online2.a        -l:decoder/kaldi-decoder.a
-l:ivector/kaldi-ivector.a        -l:gmm/kaldi-gmm.a
-l:tree/kaldi-tree.a              -l:feat/kaldi-feat.a
-l:cudamatrix/kaldi-cudamatrix.a  -l:lat/kaldi-lat.a
-l:hmm/kaldi-hmm.a                -l:nnet3/kaldi-nnet3.a
-l:transform/kaldi-transform.a    -l:matrix/kaldi-matrix.a
-l:fstext/kaldi-fstext.a          -l:util/kaldi-util.a
-l:base/kaldi-base.a              -l:nnet2/kaldi-nnet2.a
-L$ROOT/openfst-build/lib         -l:libfst.a
-L$ROOT/openblas-build/lib        -l:libopenblas.a"

# Go to build root
cd "$ROOT"

# Generate .html, .js, and .wasm
em++ $WAFLAGS -O3 $CXXFLAGS $LDFLAGS kaldi/src/nnet2/am-nnet-test.cc -o index.html

• Open the index.html in a browser, check the console for logs from the test. Note that file URL will not work, use 127.0.0.1 or something else.