build.sh

#!/usr/bin/env bash

# This script builds FFmpeg libraries without any functional features.
#
# IMPORTANT:
# The resulting library files have to be LGPL version of FFmpeg libraries.
# - Do not enable `--enable-nonfree` and `--enable-gpl`.
# - Do not enable third party library integrations like x264.
#
# This script is not meant to build useful FFmpeg libraries, but to build
# a skeleton of FFmpeg libraries that are use only during the build process of
# torchaudio.
#
# The resulting FFmpeg libraries should not be shipped either.

set -eux

prefix="${FFMPEG_ROOT}"
args=""
if [[ "$OSTYPE" == "msys" ]]; then
   args="--toolchain=msvc"
fi

build_dir=$(mktemp -d -t ffmpeg-build.XXXXXXXXXX)
cleanup() {
    rm -rf "${build_dir}"
}
trap 'cleanup $?' EXIT

(
cd "${build_dir}"
# NOTE:
# When changing the version of FFmpeg, update the README so that the link to the source points
# the same version.
curl -LsS -o ffmpeg.tar.gz https://github.com/FFmpeg/FFmpeg/archive/refs/tags/n4.1.8.tar.gz
tar -xf ffmpeg.tar.gz --strip-components 1
./configure \
    --prefix="${prefix}" \
    --disable-all \
    --disable-everything \
    --disable-programs \
    --disable-doc \
    --disable-debug \
    --disable-autodetect \
    --disable-x86asm \
    --disable-iconv \
    --disable-encoders \
    --disable-decoders \
    --disable-hwaccels \
    --disable-muxers \
    --disable-demuxers \
    --disable-parsers \
    --disable-bsfs \
    --disable-protocols \
    --disable-devices \
    --disable-filters \
    --disable-asm \
    --disable-static \
    --enable-shared \
    --enable-rpath \
    --enable-pic \
    --enable-avcodec \
    --enable-avdevice \
    --enable-avfilter \
    --enable-avformat \
    --enable-avutil ${args}

make -j install
ls ${prefix}/*
)

# macOS: Fix rpath so that the libraries are searched dynamically in user environment.
# In Linux, this is handled by `--enable-rpath` flag.
if [[ "$(uname)" == Darwin ]]; then
    avcodec=libavcodec.58
    avdevice=libavdevice.58
    avfilter=libavfilter.7
    avformat=libavformat.58
    avutil=libavutil.56

    # list up the paths to fix
    for lib in ${avcodec} ${avdevice} ${avfilter} ${avformat} ${avutil}; do
        otool -l ${prefix}/lib/${lib}.dylib | grep -B2 ${prefix}
    done

    # Replace the hardcoded paths to @rpath
    install_name_tool \
        -change ${prefix}/lib/${avutil}.dylib @rpath/${avutil}.dylib \
        -delete_rpath ${prefix}/lib \
        -id @rpath/${avcodec}.dylib \
        ${prefix}/lib/${avcodec}.dylib
    otool -l ${prefix}/lib/${avcodec}.dylib | grep -B2 ${prefix}

    install_name_tool \
        -change ${prefix}/lib/${avformat}.dylib @rpath/${avformat}.dylib \
        -change ${prefix}/lib/${avcodec}.dylib @rpath/${avcodec}.dylib \
        -change ${prefix}/lib/${avutil}.dylib @rpath/${avutil}.dylib \
        -delete_rpath ${prefix}/lib \
        -id @rpath/${avdevice}.dylib \
        ${prefix}/lib/${avdevice}.dylib
    otool -l ${prefix}/lib/${avdevice}.dylib | grep -B2 ${prefix}

    install_name_tool \
        -change ${prefix}/lib/${avutil}.dylib @rpath/${avutil}.dylib \
        -delete_rpath ${prefix}/lib \
        -id @rpath/${avfilter}.dylib \
        ${prefix}/lib/${avfilter}.dylib
    otool -l ${prefix}/lib/${avfilter}.dylib | grep -B2 ${prefix}

    install_name_tool \
        -change ${prefix}/lib/${avcodec}.dylib @rpath/${avcodec}.dylib \
        -change ${prefix}/lib/${avutil}.dylib @rpath/${avutil}.dylib \
        -delete_rpath ${prefix}/lib \
        -id @rpath/${avformat}.dylib \
        ${prefix}/lib/${avformat}.dylib
    otool -l ${prefix}/lib/${avformat}.dylib | grep -B2 ${prefix}

    install_name_tool \
        -delete_rpath ${prefix}/lib \
        -id @rpath/${avutil}.dylib \
        ${prefix}/lib/${avutil}.dylib
    otool -l ${prefix}/lib/${avutil}.dylib | grep -B2 ${prefix}
fi