The best video converter for Mac

A file that refuses to open is one of the more annoying problems in video, and it is often solved in seconds — without touching a single pixel. Crisp converts video and photos on your Mac, offline. Knowing the difference between a container and a codec tells you which conversions are free and which ones cost you quality.

The container is the box. The codec is the contents.

MP4, MOV and MKV are containers. They hold streams — video, audio, subtitles — and describe how they fit together. H.264, HEVC and AV1 are codecs: the actual compressed picture inside. The file extension tells you about the box, not what is in it, which is why two MP4 files can behave completely differently.

This explains the most common frustration on a Mac. QuickTime will not open MKV, even when the video inside is ordinary H.264 that it plays happily from an MP4. Nothing is wrong with the video; the wrapper is unsupported. Our explainer on codecs goes deeper if you want the underlying detail.

The conversion that costs nothing

If the codec inside is already one the destination supports, the streams can be copied into a new container untouched. This is called remuxing, and it has two properties worth remembering: it finishes in seconds regardless of how long the video is, and it is mathematically lossless, because the picture data is copied rather than recompressed.

That covers a surprising share of everyday conversions — most MKV to MP4 and MOV to MP4 jobs are exactly this. If a converter takes twenty minutes and warms up your Mac for one of these, it is re-encoding when it did not need to, and you are paying quality for nothing. A conversion that finishes almost instantly is a good sign, not a suspicious one.

When re-encoding is unavoidable

Sometimes the codec itself is the problem, and then the picture genuinely has to be decoded and compressed again, with the usual loss.

• The destination cannot play the codec. An older device that handles H.264 but not HEVC, for example.
• You are changing the picture. Resolution, frame rate, colour, cropping — any of these means new frames have to be written.
• Photos. Converting HEIC to JPG is always a re-encode, because the two formats compress in different ways.
• You need a smaller file. Size comes from bitrate, and changing bitrate means encoding again.

In all four cases the rule is the same: start from the original file. Each lossy generation stacks on the last, and converting an export of an export is how footage picks up that soft, blocky look.

Be careful with free online converters

Browser-based converters are convenient and they have one property people rarely think through: your file is uploaded to somebody else's computer. For a meme clip that hardly matters. For client work, medical or legal footage, family video, or anything under an agreement, it means handing a copy to a third party whose retention policy you have not read. There are also practical limits — file size caps, queues, and a re-encode applied whether or not your job needed one. Local conversion avoids all of it, and for remuxable jobs it is faster anyway.

The free option worth trying first

ffmpeg with stream copying does lossless remuxing in one short command and costs nothing. For a single MKV that will not open, it is genuinely the fastest route if you are comfortable in a terminal. It becomes tiresome with a folder of mixed files, or when you have to inspect each one to work out whether a copy is even possible.

Where Crisp fits

Conversion in Crisp is free and on-device, and it sits next to the repair tools, which matters when the file you are converting is also the one you want to clean up — doing both in one pass avoids an extra lossy generation. Free exports carry a small “Made with Crisp” mark; a one-time $99 removes it and adds batch processing for converting a folder at a time. No subscription, and no upload.