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contributing.md

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Contributing

Thank you for your interest in contributing to Livepeer Media Server.

Working on Go code

If your goal is making changes solely to Go part of the codebase, just follow Requirements section and make sure you have all dependencies to build Go scripts successfully. Debugging with Delve, GDB, or, visually, with IDE (e.g. JetBrains GoLand, Microsoft VS Code) should work fine.

Working on CGO interface and FFMpeg code

When working on CGO interface, or FFmpeg fork, chances are you might want to create a separate debug build of all components. While production build links with static libraries of Ffmpeg, it's more convenient to use shared libraries for debugging, because this way there's no need to re-build GO executable after every change in Ffmpeg code.

Preparing debug build

  1. Copy ~/compiled dir created by install_ffmpeg.sh to compiled_debug
  2. If you want to keep system-wide Ffmpeg installation, remove/rename system pkg-config (.pc) files of Ffmpeg libs (located in /usr/local/lib/pkgconfig/ on most Linux distros). Otherwise, pkg-config will prioritize system libs without debug information.
  3. FFmpeg should be already cloned after running install_ffmpeg.sh. Navigate to FFmpeg dir and run configure as below, making sure all paths are correct. 
    export ROOT=/projects/livepeer/src
export PATH="$ROOT/compiled_debug/bin":$PATH
export PKG_CONFIG_PATH="${PKG_CONFIG_PATH:-}:$ROOT/compiled_debug/lib/pkgconfig"
./configure --fatal-warnings \
    --enable-gnutls --enable-libx264 --enable-gpl \
    --enable-protocol=https,http,rtmp,file,pipe \
    --enable-muxer=mpegts,hls,segment,mp4,null --enable-demuxer=flv,mpegts,mp4,mov \
    --enable-bsf=h264_mp4toannexb,aac_adtstoasc,h264_metadata,h264_redundant_pps,extract_extradata \
    --enable-parser=aac,aac_latm,h264 \
    --enable-filter=abuffer,buffer,abuffersink,buffersink,afifo,fifo,aformat,format \
    --enable-filter=aresample,asetnsamples,fps,scale,hwdownload,select,livepeer_dnn,signature \
    --enable-encoder=aac,libx264 \
    --enable-decoder=aac,h264 \
    --extra-cflags="-I${ROOT}/compiled_debug/include -g3 -ggdb -fno-inline" \
    --extra-ldflags="-L${ROOT}/compiled_debug/lib ${EXTRA_LDFLAGS}" \
    --enable-cuda --enable-cuda-llvm --enable-cuvid --enable-nvenc --enable-decoder=h264_cuvid --enable-filter=scale_cuda --enable-encoder=h264_nvenc \
    --enable-libtensorflow \
    --prefix="$ROOT/compiled_debug" \
    --enable-debug=3                \
    --disable-optimizations \
    --disable-stripping
    --disable-static
    --enable-shared
  4. Run make install
  5. Build Go apps with debug information. Use absolute path in PKG_CONFIG_PATH to point to compiled_debug dir: 
    PKG_CONFIG_PATH=/projects/livepeer/src/compiled_debug/lib/pkgconfig go build -a -gcflags all="-N -l" cmd/scenedetection/scenedetection.go
  6. Finally, run the binary with GDB. LD_LIBRARY_PATH should point to compiled_debug dir: 
    LD_LIBRARY_PATH="../compiled_debug/lib/" gdb --args scenedetection 0 ../bbb/source.m3u P144p30fps16x9 nv 0
  7. Optionally, you can install gdbgui with pip install gdbgui and use it in place of gdb for visual debugging.

Potential issues

1. No source file named X when setting breakpoint with GDB

Make sure that:

  • Your executable is linked against (can find) correct libraries 
    LD_LIBRARY_PATH="../compiled_debug/lib/" ldd ./scenedetection
  • Your executable / libraries has debug information 
    objdump --syms compiled_debug/lib/libavcodec.so

2. Cannot cross GO->CGO->LIB boundary when stepping with GDB

Unfortunately, this is a limitation of GDB when debugging GO code. A workaround is to set separate breakpoints and navigate between them with continue.