How is libaom integrated into FFmpeg?

The integration of libaom into the FFmpeg multimedia framework allows users to encode high-quality video using the open-source AV1 codec. As the reference encoder developed by the Alliance for Open Media (AOMedia), libaom is accessible within FFmpeg via the libaom-av1 encoder wrapper. This integration enables cross-platform, command-line video compression that leverages FFmpeg’s massive filtering and multiplexing ecosystem alongside AV1’s advanced compression efficiency.

Enabling libaom in FFmpeg Compilation

Because libaom is an external third-party library, it is not built into FFmpeg by default. To use it, FFmpeg must be compiled from source with explicit configuration flags.

• The external libaom library and its development headers must be installed on the host system.
• The FFmpeg build script must be invoked with the --enable-libaom configuration flag.
• Because AV1 encoding is computationally intensive, compiling with optimization flags enabled is highly recommended to maximize performance.

Command-Line Usage and Syntax

Once compiled, libaom is invoked in the FFmpeg command line using the -c:v libaom-av1 flag. A typical encoding command specifies the video codec, a rate control method, and a speed preset to balance encoding time against file size.

ffmpeg -i input.mp4 -c:v libaom-av1 -crf 28 -b:v 0 -cpu-used 4 output.mkv

Key Encoding Parameters and Controls

FFmpeg exposes several native libaom parameters through its standard command-line interface to fine-tune the encoding process:

• Rate Control (-crf or -b:v): Constant Rate Factor (CRF) is the recommended method for file-based encoding, typically ranging from 0 to 63 (where lower values mean higher quality). Alternatively, target bitrates can be set using -b:v.
• Speed vs. Quality (-cpu-used): This parameter dictates the encoding effort. It ranges from 0 to 8, where higher numbers drastically speed up the encoding process at the expense of slight compression efficiency.
• Row-Based Multi-threading (-row-mt): Enabling this parameter (-row-mt 1) allows libaom to utilize multi-core processors more effectively, significantly reducing encoding times on modern hardware.