FFV1

FFV1, which stands for "FF video codec 1", is a lossless intra-frame video codec. It can use either variable length coding or arithmetic coding for entropy coding. The encoder and decoder are part of the free, open-source library libavcodec in the project FFmpeg since June 2003.^[1] FFV1 is also included in ffdshow or LAV Filters, which makes the video codec available to Microsoft Windows application that support system-wide codecs over Video for Windows (VfW) or DirectShow.

Video archiving

For long-term preservation of digital video sustainable container formats as well as audio/video codecs are necessary. There is no consensus to date among the archival community as to which file format or codecs should be used for preservation purposes for digital video,^[2] yet the currently proclaimed codecs are Motion JPEG 2000 (lossless)^[3] and uncompressed video.^[4]

FFV1 has turned out to be a viable addition to that choice. With compression ratios comparable to JPEG 2000 lossless and its lower computing requirements, it is already being used by professional archives as their long-term storage codec.

FFV1 is listed as a format option for long-term preservation on digital preservation sites of Library of Congress',^[5] State Records NSW^[2] and others.

The "Österreichische Mediathek", Austria's national audio/video archive has developed DVA-Profession, a Free Software solution for archive-suitable mass video digitization, using FFV1 for storing their videos. The City of Vancouver Archives is also using FFV1 (in a Matroska container) for long-term storage,^[6][7] as is Museum Victoria in Australia.

Within the video archiving domain, the interest in FFV1 is increasing, as can be seen in a thread on the AMIA-L mailing list,^[8] the PrestoCentre Forum^[9] or the Archivematica mailing list.^[10][11] In an interview for The New York Times magazine about "Tips on Archiving Family History",^[12] Bertram Lyons from the U.S. Library of Congress says:

"[...] for video, there are many choices when it comes to codecs (the way the bits are encoded/decoded to represent the visual data, e.g., ffv1, H.264, Apple ProRes) [...]"

In January 2013, the possible use and adoption of FFV1 as archiving codec is addressed in the issue of PrestoCentre's "AV Insider" magazine:^[13]

"FFV1 has many beneficial technical features [...], but adoption rates are relatively low compared with alternatives, for example JPEG2000. [...] But holding back too long only serves to self-perpetuate the status of FFV1. The adoption by Archivematica and the Austrian Mediathek with their active promotion of FFV1 along with others may start to break this vicious circle. This could lead to a virtuous circle of wider take-up, to shared development, to incorporation into commercial products and a host of other benefits for the community."

The company " NOA Audio Solutions", well known for large scale archiving solutions, announced supporting the FFV1 in their product line in July 2013.^[14]

Applications supporting FFV1

Here is a list of applications known to be able to read and/or write FFV1 video files, either natively or by installing codec packages.

Entries marked with "-" means that they generally only support either encoding or decoding.

The term "built-in" means that the application can handle FFV1 without the necessity to install additional codec packages. Applications that come with FFV1 support out of the box, usually use FFmpeg's or Libav's libraries in order to do so.

The list is far from being complete, and will be augmented over time:

Compression details

Prediction process

FFV1 is not strictly an intra-frame format; despite not using inter-frame prediction, it allows the context model to adapt over multiple frames. This can be useful for compression due to the very large size of the context table, but can be disabled to force the encoder to generate a strictly intra-frame bitstream. As the gained compression seems to decrease^[16] with later versions of FFV1 (version 2,3), the use of GOP size greater than "1" might disappear in the future.

During progressive scanning of a frame, the difference between a current pixel and its predicted value, judging by neighboring pixels, is sent to the entropy-coding process. The prediction is done as follows:

Prediction = Median( Top, Left, Top + Left - TopLeft )

The third value, "Top + Left - TopLeft", is effectively equivalent to applying the top predictor to the current and the left sample, followed by applying the left predictor to the prediction residual of the top predictor.^{[note 1]} This method, also known as the gradient, exploits both horizontal and vertical redundancy. So in simple terms the prediction is the median of the top, left, and gradient prediction methods. For improved performance and simplicity, the edges of the frame are assumed to be zero to avoid special cases. The prediction in encoding and decoding is managed using a ring buffer.

Entropy coding process

The residuals are coded using either variable-length coding or arithmetic coding. Both options use a very large context model. The "small" context model uses (11*11*11+1)/2=666 contexts based on the neighboring values of (Left-TopLeft), (TopLeft-Top), and (Top-TopRight). The "large" context model uses (11*11*5*5*5+1)/2=7563 contexts based on the same values as before, but also (TopTop - Top) and (LeftLeft-Left), where "TopTop" is the pixel two above the current one vertically, and "LeftLeft" is the pixel two to the left of the current one. In arithmetic coding, each "context" actually has 32 sub-contexts used for various portions of coding each residual, resulting in a grand total of 242,016 contexts for the "large" model. The arithmetic coder of FFV1 is very similar to (and based on) that of H.264.

Status

On April 16, 2006, a commit-message by Michael Niedermayer confirmed that the bitstream of FFV1 (version 1) is frozen:^[17]

"ffv1 and ffvhuff havnt changed since a long time and noone proposed any changes within 1 month after my warning so they are officially no longer experimental and we will gurantee decodeability of files encoded with the currenzt ffv1/ffvhuff in the future"

Codec

Version 1 (FFV1.1)

The bitstream of version 1 is frozen since April 2006,^[17] and the codec is no longer marked as experimental since March 2010.^[18]

Version 2 (FFV1.2)

Version 2 was an intermediate version, that was never officially released and should not be used for production purpose.

Version 3 (FFV1.3)

The bitstream of version 3 is frozen since August 3, 2013.^[19] The final commit marking this version as officially released for production usage was on August 26, 2013.^[20]

Documentation

Although its documentation remains incomplete, starting April 2012, efforts are being undertaken in order to improve its documentation. The current version of FFV1's technical specification document can be found on GitHub.

See also

• FFmpeg
• List of lossless compression video codecs
• Snow (codec)

Notes

References

External links

• Source code of FFV1 codec for libavcodec — Git access
• Technical Description of the FFV1 Video Codec
• Comparison of different lossless video codecs (2007)