Workflows 6 min read
Merging Multiple Videos: Normalizing Resolution, Frame Rate and Audio First
A merge is only clean when every input shares resolution, frame rate, sample aspect ratio and audio format. When they differ, players improvise — black flashes, broken seeking, audio drift. Normalize first, merge second.
The normalization checklist
- Resolution: scale everything to the smallest-common or the dominant source; upscale sparingly.
- Frame rate: one rate for all (30 is the usual compromise); mixed rates cause A/V drift.
- SAR/DAR: phone footage often carries non-square pixel flags — normalize to SAR 1:1.
- Audio: same codec (AAC), same sample rate (48 kHz), mono→stereo unified.
Concat approaches
Stream-copy concatenation works only when ALL parameters already match — instant but brittle. Re-encode merge tolerates small mismatches and fixes timestamps. When adding crossfade transitions, each clip must exceed the transition duration and audio needs matching treatment.