potterhsu/ffmpeg-transcoding-example

FFmpeg Transcoding Example

Develop a C command line application that utilizes the FFmpeg library, including Opus Codec for audio encoding support. This application should be capable of:

1. Read a media file containing audio, specifically supporting G711 and AAC codecs.
2. Transcode the media file to Opus codec.
3. Write into an MP4 file.

Knowledge

• There are two Opus encoders for FFmpeg:

  1. opus: This is the native Opus encoder that comes bundled with FFmpeg.
  2. libopus: This is the Opus encoder that uses the official Opus library.

  According to official documents opus and libopus,

  This is a native FFmpeg encoder for the Opus format. Its quality is usually worse and at best is equal to the libopus encoder.

  we choose libopus in this project.

• Opus supports only 8000, 12000, 16000, 24000, and 48000 Hz sample rates. It will be resampled if the sample rate of the input audio is not in this list.

Setup

1. Install required toolchains

   sudo apt install cmake yasm

2. Compile Opus Codec library

   1. Download source code from here (see Official Site)

   2. Compile and install

      tar -zxvf opus-1.3.1.tar.gz
      cd opus-1.3.1
      ./configure --prefix=/path/to/ffmpeg-transcoding-example/3rdparty/opus
      make -j4
      make install

3. Compile FFmpeg library

   1. Download source code from here (see Official Site)

   2. Compile and install

      tar -jxvf ffmpeg-snapshot.tar.bz2
      cd ffmpeg
      PKG_CONFIG_PATH=/path/to/ffmpeg-transcoding-example/3rdparty/opus/lib/pkgconfig \
          ./configure --prefix=/path/to/ffmpeg-transcoding-example/3rdparty/ffmpeg --enable-libopus
      make -j4
      make install

4. Check the codec of media files

   ffprobe ./inputs/sample1.alaw
   # Stream #0:0: Audio: pcm_alaw
   
   ffprobe ./inputs/sample2.aac
   # Stream #0:0: Audio: aac (LC), 48000 Hz
   
   ffprobe ./inputs/sample3.aac
   # Stream #0:0: Audio: aac (LC), 44100 Hz

5. Now your folder structure should be like

   - ffmpeg-transcoding-example
       - 3rdparty
           - ffmpeg
               - bin
               - include
               - lib
               - share
           - opus
               - include
               - lib
               - share
       - inputs
           - sample1.alaw
           - sample2.aac
           - sample3.aac
       - outputs
   

Usage

1. Compile

   mkdir build
   cd build
   cmake ..
   make -j4

2. Run

   ./ffmpeg-transcoding-example ../inputs/sample1.alaw ../outputs/sample1.mp4
   ./ffmpeg-transcoding-example ../inputs/sample2.aac ../outputs/sample2.mp4
   ./ffmpeg-transcoding-example ../inputs/sample3.aac ../outputs/sample3.mp4

3. Validate

   ffprobe ../outputs/sample1.mp4
   # Stream #0:0(und): Audio: opus
   
   ffprobe ../outputs/sample2.mp4
   # Stream #0:0(und): Audio: opus
   
   ffprobe ../outputs/sample3.mp4
   # Stream #0:0(und): Audio: opus