atrim

atrim is an audio filter in FFmpeg’s libavfilter that trims an input audio stream by discarding samples outside a specified interval. It is commonly used to remove silence at the beginning or end of a track, or to cut a section from a recording. The filter preserves audio properties such as sample rate and channel layout.

The filter accepts time-based and sample-based specifications. Time-based trimming uses start and end in seconds (or fractions), while sample-based trimming uses start_sample and end_sample. The general syntax is atrim=start=...:end=...[:start_sample=...[:end_sample=...]] and can be applied to an audio stream with -filter:a in FFmpeg command lines. If end is omitted, trimming continues to the end of the stream; if start is omitted, trimming begins at the start. Combining with asetpts=PTS-STARTPTS is common to reset timestamps after trimming.

Examples illustrate typical usage. To trim a 5 to 25 second segment from an input file and reset timestamps, you would use: ffmpeg -i input.mp3 -filter:a "atrim=start=5:end=25,asetpts=PTS-STARTPTS" output.mp3. For sample-based trimming, to keep samples 1000 through 5000, you could use: ffmpeg -i input.wav -filter:a "atrim=start_sample=1000:end_sample=5000,asetpts=PTS-STARTPTS" output.wav. Either approach can be combined with other filters as part of a complex audio processing workflow.

Notes: atrim is a standard FFmpeg filter available in typical builds. It does not perform resampling or format conversion by itself; use additional filters if needed for format changes.