The Helix YUV Codecs are two almost identical Video for Windows compatible codecs for decompressing or viewing I420 and YV12 AVI files or the output of AviSynth scripts, as well as compressing/converting to these formats. A VFW codec is necessary for full viewing/editing support for a format in VirtualDub and other VFW applications.

Most of you will already have a VFW decompressor for YV12 via the XviD DLL, and for I420 via 'MS H.263' (msh263.drv). The problem with 'MS H.263' is that it does not handle anything not a multiple of 16, or larger than 352x288. The only restriction with the Helix YUV codecs is width must be a multiple of 4.

Neither XviD nor msh263 can convert to or "compress" to I420 or YV12 though, and it is convenient to be able to convert both to and from YV12 and I420, as well as have a native codec for both formats, always knowing which codec is responsible for handling the format, and knowing exactly how it is handled. And I also like to see 'YV12' or 'I420' as the format, when right clicking on AVI file, instead of 'XviD' or 'MS H.263', since it is the codec and not the 4CC code that is displayed.

What is I420?

It is simply YV12 with the chroma planes swapped.

Helix YUV Codecs contains :

- I420 VFW Compressor/Decompressor
- YV12 VFW Compressor/Decompressor

Features of Helix YUV Codecs 1.2 :

- Both decode I420 and YV12.
- Fast color conversions to all common RGB formats, YUY2, and of course I420 and YV12 when requested.
- i420vfw.dll encodes to I420, yv12vfw.dll encodes to YV12.
- Otherwise identical, both encoders accept common input formats, and losslessly converts to and from both color spaces, i.e. with "Fast recompress" in VirtualDub, there is no conversion via RGB.

Known issues :

- Width has to be a multiple of 4, and the height a multiple of 2.

Changes in Helix YUV Codecs 1.2 :

- Fixed problem with swapped U and V planes when saving to I420/YV12 from other formats than I420/YV12.