ffmpeg-resampler

ffmpeg -i input_file [resampling_options] output_file

Example Audio Resampling:
ffmpeg -i input.wav -ar 48000 -ac 2 output.flac

Example Video Scaling:
ffmpeg -i input.mp4 -vf "scale=1280:-1" output.mkv

-i
    Specifies the input multimedia file to be processed.

-ar
    Sets the target audio sample rate (e.g., 44100, 48000 Hz) for resampling.

-ac
    Defines the number of audio channels (e.g., 1 for mono, 2 for stereo) for resampling.

-filter:a
    Applies an audio filtergraph. For resampling, the aresample filter is commonly used (e.g., -filter:a "aresample=resampler=soxr:precision=28").

-filter:v
    Applies a video filtergraph. The scale filter is used for changing video resolution (e.g., -filter:v "scale=1920:1080").

-c:a
    Specifies the audio encoder to use for the output (e.g., aac, libmp3lame).

-c:v
    Specifies the video encoder to use for the output (e.g., libx264, libvpx).

-map
    Selects specific streams from the input to include in the output. Useful for discarding unwanted streams or mapping specific audio/video tracks.

ffmpeg-resampler refers to the robust audio and video resampling capabilities built into the FFmpeg multimedia framework, rather than a standalone command. FFmpeg is a versatile, open-source project that handles various multimedia tasks, including conversion, streaming, and editing.

Resampling involves altering the characteristics of audio or video streams. For audio, this primarily means changing the sample rate (e.g., from 44.1 kHz to 48 kHz), adjusting the number of audio channels (e.g., stereo to mono, or upmixing), or converting sample formats. For video, it typically refers to scaling (changing resolution), deinterlacing, or converting pixel formats. FFmpeg leverages specialized libraries like libswresample for high-quality audio resampling and libswscale for efficient video scaling and pixel format conversions.

The resampling process within FFmpeg is highly configurable, offering various quality settings, algorithms, and filter options to achieve precise control over the output. It is widely used in multimedia production, broadcasting, and streaming workflows to ensure compatibility and optimize media for different target platforms or bandwidths.

While powerful, resampling with FFmpeg requires careful consideration. Incorrect settings or low-quality algorithms can introduce audio artifacts (aliasing, ringing) or video quality degradation (blurriness, jagged edges). High-quality resampling algorithms (like soxr for audio or Lanczos for video) can be CPU-intensive and increase processing time. Always test output quality and check for potential issues before deploying resampled media in production environments.

For high-quality audio resampling, FFmpeg's aresample audio filter can be configured with various options like resampler (e.g., 'soxr' for extreme quality), precision, and filter_size to control the resampling algorithm's characteristics and output fidelity. Default settings are often sufficient, but for critical applications, experimenting with these options can yield superior results.

When using the scale video filter, FFmpeg allows specifying the scaling algorithm via the -sws_flags global option or directly within the scale filter using the flags option. Common algorithms include bilinear (fast, good for downscaling), bicubic (good balance of speed and quality), and lanczos (high quality, good for upscaling, slower). The choice depends on the desired balance between processing speed and visual quality.

The resampling capabilities within FFmpeg have evolved significantly since its inception in 2000. Key to this development is the libswresample library, specifically designed for high-quality audio resampling, channel mixing, and sample format conversion, providing a unified and optimized solution for audio manipulation. Similarly, libswscale handles video scaling, pixel format conversion, and interlacing/deinterlacing, offering various scaling algorithms. These libraries continuously receive updates, incorporating new algorithms and optimizations to maintain FFmpeg's position as a leading multimedia tool for demanding tasks like resampling.

ffmpeg(1), ffprobe(1), ffplay(1), ffmpeg-filters(1), sox(1)