DNxHD/VC-3 Compliance Issue

It has been discovered that a standards compliance issue exists. This affects DNxHD media created by both Avid’s hardware and software products. The media is not compliant with the SMPTE VC-3 specification. The compressed data is NOT corrupted, but there are three bit-fields that are affected. All Avid’s current and past products decode DNxHD media, but as Avid’s customers incorporate 3rd party VC-3 products, they will encounter this issue due to the non-compliant bit-fields.

The problem involves three separate fields in the picture header of a DNxHD 1080i encoded frame. Avid’s software and hardware DNxHD codecs currently create media that have different combinations of non-compliance. The hardware codec compliance issue is limited to Avid Nitris DX models.

  1. The Active Line Height (ALPF and NAL) is set to 1080 but should be set to 540 for interlaced frames. (S/W codec only.) (See Section 7.1.3 of SMPTE 2019-1-2008)
  2. The Source_Scan_Type (SST) is set to 0 but should be set to 1 for interlaced frames. (H/W codec only). (See Section 7.1.3 of SMPTE 2019-1-2008)
  3. The Field or Frame Encoding (FFE) in the Coding Control B area is set to 1 but should be set to0 for interlaced frames. (H/W codec only.) (See Section 7.1.5 of SMPTE 2019-1-2008)

In all cases progressive media (720p and 1080p encoded frames) is compliant.

To correct this compliance issue, Avid is releasing a new version of the DNxHD optimized binaries as well as a new version of the QuickTime DNxHD codec. This release of Avid Media Composer v4.0, Avid Symphony v4.0 and Avid Newscutter v8.0 contains updated codecs to create compliant media.

The updated codec is backwards compatible, decoding both compliant and non-compliant media. A codec will be made available for previous versions (prior to v4.0 and v7.0) of Avid Media Composer, Avid Symphony and Avid Newscutter.

When you play compliant DNxHD media in a previous editor application, it may result in frames being decompressed incorrectly. This is characterized by only the top half of a frame being decompressed with the bottom half of the image displaying in with either black or green. If you install the updated codec in these earlier editor applications, it will correct the decoding.