Anyone who has tried to edit 4K files from a smartphone or a mirrorless camera on a laptop knows the feeling: the timeline stutters, scrubbing is slow, every cut means waiting. Often this is not down to the computer's raw power but to the type of codec the files were recorded with. Codecs designed for distribution and codecs designed for editing have opposite goals, and understanding the difference lets you work far more smoothly.
Acquisition, editing and delivery codecs
Acquisition codecs
Consumer cameras almost always record H.264 or HEVC with long GOPs. It is a sensible choice for them: small files, memory cards that last longer. But to decode any given frame the computer must rebuild every frame it depends on, starting from the previous keyframe. When you scrub the timeline back and forth, this work is repeated constantly.
Editing codecs
Intermediate codecs such as Apple ProRes and Avid DNxHD/DNxHR are designed the other way round:
- every frame is independent (intra-frame compression only), so access to any point is immediate;
- decoding is light on the processor;
- quality stays high even after several generations of re-encoding;
- they support 10 bit and 4:2:2 or 4:4:4 subsampling.
The price is space: a ProRes file takes many times the space of an H.264 file of the same length.
Delivery codecs
At the end of the edit you export to an efficient codec, such as H.264, HEVC or AV1, suited to the audience and the platform.
The ProRes variants
ProRes is developed by Apple and comes in several variants, from lightest to heaviest:
| Variant | Typical use |
|---|---|
| ProRes 422 Proxy | light working files for offline editing |
| ProRes 422 LT | editing with limited storage |
| ProRes 422 | general post-production use |
| ProRes 422 HQ | high quality for masters and grading |
| ProRes 4444 / 4444 XQ | graphics, effects, alpha channel for transparency |
On macOS ProRes is supported natively; on Windows and Linux the main editing programs read it and many write it, and FFmpeg has a ProRes encoder.
DNxHD and DNxHR
DNxHD was created for high definition up to 1080p; DNxHR extends it to any resolution, including 4K. Here too there are different profiles, such as LB (low bandwidth, suited to proxies), SQ, HQ, 10-bit HQX and 444. DNxHR is typically used in MXF or MOV containers and is very common on Windows and in television production.
Three ways of working
1. Editing the original files directly
This is the simplest solution and works well if the computer has efficient hardware decoding for the camera's codec. Many recent processors and graphics cards decode H.264 and HEVC in hardware, but not every variant: 10-bit 4:2:2 HEVC files, for example, are not supported by all hardware.
2. Transcoding everything to an intermediate codec
Before editing, all files are converted to ProRes or DNxHR and you work only on those. Editing becomes smooth and the files keep a quality suitable for the final export as well. It does, however, require a lot of disk space.
With FFmpeg a conversion to ProRes 422 HQ looks like this:
ffmpeg -i clip.mp4 -c:v prores_ks -profile:v 3 -pix_fmt yuv422p10le -c:a pcm_s16le clip.mov
3. Working with proxies
This is the most common compromise. You generate light, low-resolution copies of the original files, for example in ProRes Proxy or DNxHR LB at 960×540 or 1280×720, and edit with those. At export time the program automatically relinks the original files.
Advantages: - smooth editing even on modest computers; - limited storage use; - the final export still uses the original quality.
Things to watch: - proxies must have the same frame rate and duration as the originals; - file names and folder structure must stay consistent, or relinking fails; - grading and sharpness checks must be done on the originals, not on the proxies.
Organising storage
A clear organisation avoids many problems:
- one folder for the originals, which must never be modified or renamed;
- a separate folder for proxies or intermediate files, ideally on a fast drive;
- one folder for exports;
- a backup of the originals on another medium before you start.
Exporting the master
When the edit is finished, it is best to export a master first in a high-quality intermediate codec, such as ProRes 422 HQ, and derive the web or platform versions from it. If a different format is needed in future, you start again from the master without reopening the project and without piling up losses.
In short
- Camera codecs are efficient but heavy to decode during editing.
- ProRes and DNxHR use independent frames and are designed for editing.
- Proxies allow smooth editing while keeping the original quality on export.
- Proxies and originals must share frame rate, duration and consistent names.
- Export a high-quality master and derive delivery versions from it.
