DNxHD codec

Avid DNxHD, which stands for "Digital Nonlinear Extensible High Definition", is a lossy high-definition video post-production codec engineered for multi-generation compositing with reduced storage and bandwidth requirements. It is an implementation of SMPTE VC-3 standard.^[1] DNxHD codec was developed by Avid Technology, Inc.

Overview

DNxHD is a video codec intended to be usable as both an intermediate format suitable for use while editing and as a presentation format. DNxHD offers a choice of three user-selectable bit rates: 220 Mbit/s with a bit depth of 10 or 8 bits, and 145 or 36 Mbit/s with a bit depth of 8 bits.

DNxHD data is typically stored in an MXF container, although it can also be stored in a Quicktime container.

On February 13, 2008 Avid reported that DNxHD was approved as compliant with the SMPTE VC3 standard.^[2]

DNxHD is intended to be an open standard, but as of March 2008, has remained effectively a proprietary Avid format. The source code for the Avid DNxHD codec is freely available from Avid for internal evaluation and review, although commercial use requires Avid licensing approval. It has been commercially licensed to a number of companies including Ikegami, FilmLight, Harris Corporation, JVC, Seachange and EVS Broadcast Equipment.^[3]

Implementations

DNxHD was first supported in Avid DS Nitris (Sept 2004), then Avid Media Composer Adrenaline with the DNxcel option (Dec 2004) and finally by Avid Symphony Nitris (Dec 2005). Xpress Pro is limited to using DNxHD 8-bit compression, which is either imported from file or captured using a Media Composer with Adrenaline hardware. Media Composer 2.5 also allows editing of fully uncompressed HD material that was either imported or captured on a Symphony Nitris or DS Nitris system. Ikegami's Editcam camera system is unique in its support for DNxHD, and records directly to DNxHD encoded video. Such material is immediately accessible by editing platforms that directly support the DNxHD codec.

A standalone Quicktime codec for both Windows XP and Mac OS X is available to create and play Quicktime files containing DNxHD material.

Since September 2007 the open source FFmpeg project is providing 8-bit (but not 10-bit) VC-3/DNxHD encoding and decoding features thanks to BBC Research who sponsored the project and Baptiste Coudurier who implemented it. It is included in stable version 0.5 of FFmpeg, released on March 10, 2009.^[4][5] (ffmpeg -i <input_file> -vcodec dnxhd -b <bitrate> -an output.mov). This allows Linux non-linear video editors Cinelerra and Kdenlive to use DNxHD.

Technical details

DNxHD is very similar to JPEG. Every frame is independent and consists of VLC-coded DCT coefficients.

Header consists of many parts and may include quantization tables and 2048 bits of user data. Also each frame has two GUIDs and timestamp. The frame header is packed into big-endian dwords. Actual frame data consists of packed macroblocks using a technique almost identical to JPEG: DC prediction and variable-length codes with run length encoding for other 63 coefficients. DC coefficient is not quantized.

The codec supports alpha channel information.

VC-3

The DNxHD codec was submitted to the SMPTE organization as the framework for the VC-3 family of standards. It was approved as SMPTE VC-3 after a two year testing and validation process in 2008 and 2009:^[1][2][6][7]

• SMPTE 2019-1-2008 VC-3 Picture Compression and Data Stream Format
• SMPTE 2019-3-2008 VC-3 Type Data Stream Mapping Over SDTI
• SMPTE 2019-4-2009 Mapping VC-3 Coding Units into the MXF Generic Container
• RP (Recommended Practices) 2019-2-2009 VC-3 Decoder and Bitstream Conformance

References

1. ^ ^{a b} Avid Technology, Inc. (2008-02-13). "Avid DNxHD is First Codec Compliant with SMPTE VC-3". http://www.avid.com/US/press-room/DNxHD-SMPTE-VC3. Retrieved 2010-08-19. 
2. ^ ^{a b} "Avid DNxHD is First Codec Compliant with SMPTE VC-3". Archived from the original on 2008-02-15. http://web.archive.org/web/20080215145411/http://www.avid.com/company/releases/2008/080213_dnxhd_avid.html. Retrieved 2008-02-13. ^{[dead link]}
3. ^ "Avid DNxHD Licensees". http://www.avid.com/dnxhd/dnxhd-licensees.html. Retrieved 2008-08-25. ^{[dead link]}
4. ^ FFmpeg version 0.5, Retrieved on 2009-08-09
5. ^ FFmpeg General documentation - Video codecs, Retrieved on 2009-08-09
6. ^ SMPTE (PDF), Standards development and the SMPTE role, http://www.smpte.org/sections/section_washingtondc/washington_previous/wash_dec05/Symes061221.pdf, retrieved 2010-08-18 
7. ^ "Numerical SMPTE Standards List". http://store.smpte.org/category-s/22.htm. Retrieved 2010-08-18. 

External links

• Avid DNxHD Codec Features
• Avid Codec Downloads
• Ikegami Editcam press release
• MainConcept VC-3 SDK
• Nethra VC-3 codec chip