FFmpeg Essentials: Containers vs Codecs (MP4, MKV, MOV)

Tue Jul 02 2024

Understand containers vs codecs, when to remux or transcode, and enable fast start for MP4.

Containers like MP4 and MKV store streams encoded by codecs like H.264 and AAC. Knowing the difference helps you choose the right workflow and avoid needless quality loss.

Containers vs Codecs

  • Containers: MP4, MKV, MOV, WebM — wrap streams, subtitles, and metadata.
  • Codecs: H.264/H.265/VP9/AV1 (video), AAC/Opus/FLAC/MP3 (audio).

Practical Tasks

# Remux to MKV (no quality loss)
ffmpeg -i input.mp4 -c copy output.mkv

# Move MP4 moov atom for fast start
ffmpeg -i input.mp4 -c copy -movflags +faststart output_faststart.mp4

# WebM (VP9/Opus) encode
ffmpeg -i input.mp4 -c:v libvpx-vp9 -b:v 0 -crf 32 -c:a libopus -b:a 96k out.webm

Pitfalls

  • MP4 text subs need mov_text.
  • Some platforms have limited MKV support.

Start by remuxing when possible; transcode only when you must change codecs or apply filters.