Apple ProRes: Difference between revisions

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* custom hybrid [[Golomb|Golomb-Rice]] / [ Exponential Golomb] coding for DCT coefficients
* custom hybrid [[Golomb|Golomb-Rice]] / [ Exponential Golomb] coding for DCT coefficients
* [[Run_Length_Encoding|run-lenght coding]]
* [[Run_Length_Encoding|run-length coding]]
* [[Differential_Coding|differential coding]]
* [[Differential_Coding|differential coding]]
* [[Scalar_Quantization|scalar quantization]]
* [[Scalar_Quantization|scalar quantization]]

Revision as of 12:12, 20 June 2011

ProRes Introduction

Apple ProRes is a family of proprietary video codecs used for storing and editing high definition video data in Apple's Final Cut Pro. Apple's official whitepaper lists the codec's key features as being:

  • intra-only codecs
  • visually lossless compression (i.e. compressed images cannot be distinguished from the original by a human observer)
  • 4:2:2 / 4:4:4:4 source material
  • 10-bit (12-bit for ProRes 4444) sample depth
  • variable bitrate

ProRes 422 Standard Definition / High Quality codec

ProRes 422 SD/HQ is the same codec operating on two different bitrates (flavours). Two different FOURCCs are used in order to indicate each flavour:

Flavour name FOURCC Bitrate
Standard Definition (SD) 'apcn' 145 Mbps
High Quality (HQ) 'apch' 220 Mbps

ProRes algorithm is based on the Discrete cosine transform (further DCT) and utilizes the following compression techniques:

The bitstream of the ProRes 422 has been designed to provide the following additional features:

  • frame-level multi-threaded encoding/decoding depending on available CPU cores
  • spatial scalability providing the possibility to decode a video at different partial resolutions (1/2, 1/4, 1/8 of the full size and so on). ProRes is capable of saving CPU cycles while decoding at smaller resolutions due to a special bitstream layout enabling partial bitstream access and parsing.

Binary packages and compatibility

ProRes codec is currently available as the following binary libraries:

Lib Name Version Supported OS Supported Architecture Encoding Decoding
AppleProRes422.component 1.0.2 (Build 46) Mac OS X PowerPC Yes Yes
AppleProResDecoder.qtx Windows x86 No Yes
AppleProResCodec.component 2.0 (Build 224) Mac OS X PowerPC/x86 Yes Yes
AppleProResDecoder.component 2.0.1 (Build 227) Mac OS X PowerPC/x86 No Yes

Frame layout

A typical ProRes 422 frame has the following layout:

       Frame container atom
           Frame header
            Picture 1
 Picture 2 (interlaced frames only)

Frame container atom

At the beginning of each frame the frame container atom is located. It has the classical QuickTime atom structure with the ID set to the undocumented ProRes frame type ID:

Field size Field name Description
4 bytes size frame size in bytes
4 bytes type 'icpf' ("image codec prores frame"?)

All data is stored in the big-endian format. The value of the field "size" must match frame size from the movie container.

Frame header

A frame header stores description information, such as frame dimension, frame structure (progressive/interlaced), color information and the like. All data is stored in the big-endian format.

Field size Field name Value Description
2 bytes hdrSize size of this header in bytes. Must be at least 28 bytes long.
2 bytes version
  • "0" - supported in all known decoders
  • "1" - supported in the version 2.0 only
header version.
4 bytes vendorID? 'apl0' Ignored in all known decoders.
2 bytes frameWidth Width of encoded frame.
2 bytes frameHeight Height of encoded frame.
1 byte frameFlags

layout: AAxxBBxx where

  • bits AA = sample depth?
  • bits BB = frame type:
    • "0" - progressive
    • "1" - interlaced (top-field first)
    • "2" - interlaced (bottom-field first)
Frame structure flags.
3 bytes reserved1 0 Ignored in the decoder v1. It has some meaning in the version 2.0 that need to be clarified.
1 byte colorMatrix
  • "1" = ITU-R BT.709-2 / SMPTE 274M-1995 / SMPTE 296M-1997
  • "6" = ITU-R BT.601-4 / SMPTE 170M-1994 / SMPTE 293M-1996
Color matrix ID for color conversion between YUV and RGB (see below).
2 bytes reserved2 0 Ignored.
1 byte QMatFlags

layout: xxxxxxCD where

Custom quantization matrices presence indicators.
64 bytes QMatLuma Custom quantization matrix for luminance. Only present if indicated by the bit "C" of the QMatFlags.
64 bytes QMatChroma Custom quantization matrix for chrominance. Only present if indicated by the bit "D" of the QMatFlags.