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Audio concatenation (merging) appends the samples of each file in sequence. The simplest case — two WAV files at the same sample rate — involves no encoding at all: the PCM data from file 2 is appended to file 1. When input files differ in sample rate, channel count, or codec, the merger must first normalise all inputs to a common specification before concatenation. FFmpeg's concat demuxer handles this transparently, but it means one encode pass occurs when mixing formats.

Unwanted gaps at join points usually come from silent padding at the beginning or end of source files, or from mismatched sample rates requiring resampling. To avoid gaps: (1) trim each source file with the Audio Cutter to remove leading and trailing silence before merging; (2) ensure all files use the same sample rate and channel count if possible; (3) for music that needs smooth transitions, consider using audio editing software for crossfades — simple concatenation does not blend the endings and beginnings of tracks.

For final delivery merges (podcast episodes, audiobooks, mixes), MP3 at 128 kbps stereo is the universal choice — compatible with every platform and device. For professional output that will be processed further, choose WAV for maximum quality and editing flexibility. If you are building a lossless archive from lossless sources, FLAC preserves every sample without the storage overhead of WAV. Avoid re-merging from already-merged lossy files — the generational quality loss accumulates.

A typical podcast assembly workflow: (1) record intro, main content, and outro as separate WAV files; (2) use the Noise Remover on each segment; (3) use the Audio Cutter to trim silence from the start and end of each segment; (4) upload all segments to the Audio Merger in the correct order; (5) download the merged WAV; (6) use the Audio Compressor to encode the final episode to 128 kbps MP3 for hosting. Total time: under 10 minutes for a one-hour episode.

If your source files have different sample rates (e.g., one at 44.1 kHz and another at 48 kHz), the merger must resample all files to a common rate before concatenation. We default to the sample rate of the first uploaded file. To avoid resampling artefacts, standardise your recordings at a single sample rate before merging — 44.1 kHz for music projects, 48 kHz for video and broadcast projects. Resampling with a high-quality algorithm (as FFmpeg uses) is transparent at typical listening levels, but preserving a uniform sample rate is always best practice.