Compress Video From the Terminal on macOS (avconvert and ffmpeg)

avconvert ships with macOS, so there is nothing to install. It uses Apple’s own encoders and the same presets as the Finder “Encode Selected Video Files” action. Pick a preset, a source and an output:

avconvert --source in.mov --preset PresetHEVC1920x1080 --output out.mp4 --progress --replace

Run avconvert --help to list every preset. The useful ones for shrinking files are Preset1920x1080, Preset1280x720, PresetHEVC1920x1080 and PresetMediumQuality. There is no CRF or bitrate flag. You choose a preset and accept what it gives you.

Two flags help. --start and --duration trim the clip while encoding. --multiPass asks for a slower, higher quality pass where the codec supports it. By default avconvert filters privacy-sensitive metadata, and --disableMetadataFilter turns that off.

ffmpeg is not part of macOS. Install it with Homebrew (brew install ffmpeg). Then the quality knob is CRF: lower is bigger and sharper, higher is smaller. For H.264, 23 is the default and 26 to 28 is a common range for sharing.

# H.264, plays everywhere
ffmpeg -i in.mov -c:v h264 -crf 26 -preset medium -c:a aac -b:a 128k out.mp4

# H.265 (HEVC), smaller at the same look, slower to encode
ffmpeg -i in.mov -c:v hevc -crf 28 -tag:v hvc1 -c:a aac -b:a 128k out.mp4

# Shrink the resolution too (keeps aspect ratio, even width)
ffmpeg -i in.mov -vf scale=1280:-2 -c:v h264 -crf 26 -c:a aac -b:a 128k out.mp4

The -tag:v hvc1 flag matters for H.265. Without it, QuickTime and iPhones often refuse to play the file. The -preset flag trades time for size: slow makes smaller files than medium, and veryfast makes bigger ones.

Want the reasoning behind the two codecs? See H.265 vs H.264.

We encoded one 20 second, 1920 by 1080, 30 fps H.264 clip (33.0 MB, generated with ffmpeg’s testsrc2 pattern plus a sine tone) on an Apple Silicon Mac running macOS 27.0.1 with ffmpeg 8.1.1. A test pattern is not a camera clip, so treat the ratios as an illustration. Real footage compresses differently.

Two things to read from this. First, the CRF commands gave us control and the smallest files, but avconvert needed no install and no flag tuning. Second, H.265 was not smaller here. That is a quirk of a synthetic, very sharp test pattern at our chosen CRF values. On real footage H.265 usually wins at equal quality, but check your own clip rather than trusting a rule. Our compress video on Mac guide has results on real footage.

A shell loop does it. This one writes a copy next to each original and never overwrites the source:

for f in *.mov; do
  ffmpeg -n -i "$f" -c:v h264 -crf 26 -c:a aac -b:a 128k "${f%.mov}_small.mp4"
done

-n tells ffmpeg to skip files that already exist. For avconvert, swap the command inside the loop and keep --replace off. Loops run one file at a time, so a long folder takes a long time. For a point-and-click version, read how to batch compress videos on a Mac.

• Forgetting -c:a aac. ffmpeg then copies or re-picks audio you did not choose.
• Using an odd scale width. H.264 needs even dimensions, so use scale=1280:-2, not -1.
• Putting -ss after -i when you only want a quick trim. Before -i it seeks faster.
• Setting CRF too high on text or screen recordings. Sharp edges show blocks first. Screen recordings like a lower number than camera clips.
• Writing the output over the input. Always give a new file name.

If you are comfortable in a terminal and compressing one clip, avconvert and ffmpeg are free and enough. Use them. You also get exact control over every flag, which Smol does not try to match. Smol is not a scripting tool for servers either.

Smol earns its one-time $29 when you would rather not write a loop: drop a mixed folder of videos on it, pick H.265 or H.264 and a quality, and get a copy of each next to the original. It also adds a Finder right-click action, and nothing is uploaded. Details are on the buy page. If you are still comparing options, see the best video compressor for Mac.