ProRes is a family of high-definition video compression formats developed by Apple.
It is an intermediate codec, intended for use during video editing. Recently, new cameras recording directly in ProRes (Arri Alexa series) have allowed a simplified workflow.
Family members are ProRes 422, ProRes HQ, ProRes 4444 (10bit).
It uses lossy spatial compression, but no temporal compression: The data to render a given frame is not spread over the data corresponding to other frames.
Two media profiles are usually be found: 1920x1080 and 1280x720. ProRes clips are usually found in QuickTime .mov containers.
Apple proposes a free Pro Res decoder for Mac and Windows.
Download: Mac Windows
ProRes encoder is not available for free. It comes bundled with Apple professional video applications like Final Cut Pro. Treasured just needs the decoder to preview a damaged ProRes file.
Failure modes:
The causes of failure reported by ProRes users needing to repair files are:- Loss of power during transfer of files or recording. System shutdown.
- Recorder (AJA Ki Pro, ...) not ready when drive is ejected (files closing was not complete)
- Device was turned off during recording (clip not finalized)
- Software (Wirecast, Blackmagic Media Express, ...) unexpectedly quits (crash) during capture
- Software freezes in the middle of broadcast to disk
- Loss of HD-SDI or HDMI signal
- Accidental deletion of files
- After recording, the file is damaged and will not playback on QuickTime or on Key Pro unit
- Clips retrieved from archive storage are unplayable
- Card ejected from device too early, is incorrectly unmounted
- Recorder unit is overheating, causing malfunction
- Drive (or RAID) filled up and stopped recording. It didn't finish wrapping and writing the QT files.
- AJA Ki Pro indicates dropped frames error and stops recording
- After Log and Capture from tape (Sony HDV deck, ...) the clip is unplayable
Repairability
ProRes is relatively easy to repair and gives excellent results. Video and audio are recovered at original quality.
Huge ProRes file (tens to hundreds of GB) are not a problem for Treasured and our remote repair system, since only around 100 MB of data need to be sent via Internet. With a small sample, we can figure out the repair technique and send the repair program to the customer.
A good file in the request is recommended.
Even if the good file contains only a few frames, the fact that it was encoded with the exact settings of the damaged file will provide useful information:
- Sample description (can be apcn, apch, apcs or ap4h in the stsd atom)
- Audio format and channels layout
This information can be guessed from a damaged file, but through a very lengthy trial-and-error iterative process.
How to repair a corrupted ProRes movie
Each ProRes 422 frame begins with a pattern of 8 bytes:
aabbccdd 69637066 ....icpf
where aabbccdd encodes the length of the frame (length includes those 8 header bytes).
Techniques used to fix clips are:
- Reindexing to repair the video track
- Audio Scraping to extract the audio tracks
