What is YV12?
These are several different ways to represent colors. For example: YUV and RGB colorspace. In YUV colorspace there is one component that represent lightness (luma) and two other components that represent color (chroma). As long as the luma is conveyed with full detail, detail in the chroma components can be reduced by subsampling (filtering, or averaging) which can be done in several ways (thus there are multiple formats for storing a picture in YUV colorspace). YV12 is such a format (where chroma is shared in every 2x2 pixel block) that is supported by AviSynth. Many important codecs stored the video in YV12: MPEG-4 (x264, XviD, DivX and many others), MPEG-2 on DVDs, MPEG-1 and MJPEG.
The subsampling used by YV12 is also called "4:2:0" compared to "4:2:2" which is used by YUY2 and UYVY.
Where can I download the latest stable AviSynth version which supports YV12?
"AviSynth v2.57" (and more recent versions) can be downloaded here.
Where can I download the DGIndex/DGDecode plugin, which supports YV12, to import MPEG-1/MPEG-2/TS/PVA in AviSynth?
The latest DGIndex/DGDecode combo can be downloaded here.
Which encoding programs support YV12?
The regular builds of Virtualdub (by Avery Lee) have YV12 support in fast recompress mode since v1.5.6. There are also two another options for encoding to DivX/XviD:
There is a modified version (called VirtualdubMod) which has YV12 support: This modification (by pulco-citron, Suiryc and Belgabor) has OGM and AVS-preview support. It can be downloaded here. In order to use the YV12 support (without doing any color conversions) you have to load your AVI in VirtualdubMod and select "fast recompress". For easy (and fast) YV12 support, you can also try out the command line utility AVS2AVI - compresses video from an AviSynth script using any VFW codec, see also here.
How do I use v2.5x if the encoding programs can't handle YV12 (like TMPGEnc or CCE SP)?
Using TMPGEnc you have to add the line "ConvertToRGB24" (with proper "interlaced" option) to your script, and for CCE SP you need to add the line "ConvertToYUY2" to your script, since Windows has no internal YV12 compressor.
You can also install some YV12 decompressor (codec) which will decompress the YV12-AVI for you when loading the avi in TMPGEnc or CCE SP.
What will be the main advantages of processing in YV12?
- speed increase:
- That depends entirely on the external plugins whether they will have YV12 support or not. Speed increases like 25-35 percent are expected. Of course there will only be a large speed increase if both your source and target are in YV12, for example in DVD to DivX/Xvid conversions.
- no color conversions:
- The colour information doesn't get interpolated (so often) and thus stays more realistic.
MPEG-2 encoders such as CCE, Procoder and TMPGEnc can't handle YV12 input directly. CCE and Procoder needs YUY2, and TMPGEnc RGB24. This only means that the last line of AviSynth must be a ConvertToYUY2 (for CCE/Procoder, or ConvertToRGB24 for TMPGEnc) call, and that you will not be able to take full advantage of YV12 colorspace. Still there are two advantages:
- All internal filtering in AviSynth will be faster though (less data to filter, better structure to filter, and a very fast conversion from YV12 to YUY2), and you will definitely be able to tell the difference between v2.06 and v2.5.
- If you are making a progressive clip there is another advantage. Putting off the YV12->YUY2 conversion until the end of the script allows you to first IVTC or Deinterlace to create progressive frames. But the YV12 to YUY2 conversion for progressive frames maintains more chroma detail than it does for interlaced or field-based frames.
The color conversions: CCE: YV12 -> YUY2 -> YV12 TMPGEnc: YV12 -> RGB24 -> YV12
How do I use VirtualDub/VirtualDubMod such that there are no unnecessary color conversions?
Just load your avs file in VirtualDub/VirtualdubMod and set the video on "Fast recompress". In this mode the process will stay in YV12 (all the necessary filtering has to be done in AviSynth itself). Under compression select a codec which support YV12, like Xvid, DivX5, RealVideo (provided you download the lastest binaries) or 3ivx D4 (provided you download the lastest binaries). Note that DivX3/4 also supports YV12, except that PIV users could experience crashes when encoding to DivX4 in YV12. If you want to preview the video you also need a YV12 decompressor.
Which internal filters support YV12?
In principal all internal filters support YV12 natively. Which color formats the filters support is specified in the documentation.
Which external plugins support YV12?
Are there any disadvantages of processing in YV12?
- There is a degradation of color information in YV12, which is often acceptable, but not for high quality processing and interlaced material, where it is better to use YUY2 which is less subsampled.
- If source format is not YV12 (analog capture, DV) or final encoding format is not YV12, then color format conversion will results in chroma interpolation with some quality decreasing.
- Filtering of subsampled chroma can result in some chroma broadening relatively luminocity pixels, especially for interlaced video.
- Because the chroma in interlaced YV12 video occurs on alternating lines, it is necessary to use a different upsampling/downsampling method when converting between YV12 and YUV 4:2:2 or RGB. This can lead to chroma upsampling/downsampling errors if the wrong color space conversion method is used on the video.
- If YV12 video is stored in an AVI container, there is no metadata to indicate whether the video is interlaced or progressive. This means that an application or component doing color space conversion has no easy way of choosing the correct conversion method (interlaced or progressive). Most color space converters assume progressive which can lead to chroma upsampling/downsampling errors when interlaced video is processed in such an environment.
How do I know which colorspace I'm using at a given place in my script?
To see which colorspace you are using at a given place in your script, add:
... and AviSynth will give you much information about colorspace amongst other things!
Colors are swapped when I load a DivX file in AviSynth v2.5?
This happens due to a bug in old versions of DivX5. Download the latest binaries or use "SwapUV(clip)".
I installed AviSynth v2.5 and get the following error message: "Couldn't locate decompressor for format 'YV12' (unknown)."?
Install a codec which supports YV12. DivX5 or one of the recent XviD or Helix YUV codec or some other (ffvfw, ffdshow). If that still doesn't work, modify your registry as explained in the next question.
I installed AviSynth v2.5 and DivX5 (or one of the latest Xvid builds of Koepi), all I got is a black screen when opening my avs in VirtualDub/VirtualDubMod/MPEG-2 encoder?
Ok, apparently your video is not decompressed by DivX 5.02 (or XviD). Try to use VCSwap utility for hot swapping video codecs.
Advanced user can also do it by hand. Go to your windows-dir and rename a file called MSYUV.DLL, or add the following to your registry file:
REGEDIT4 [HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Drivers32] "VIDC.YV12"="divx.dll"
Replace "divx.dll" by "xvid.dll" for xvid v0.9 or "xvidvfw.dll" for xvid v1.0.
Are there any lossless YV12 codecs, which I can use for capturing for example?
Capturing in YV12 is not recommended due to issues of interlacing and chroma; YUY2 will generally pose fewer problems. A lossless YV12 codec is more useful for saving intermediate files before a multi-pass encode, to avoid having to run a CPU-intensive script several times. There are several lossless YV12 codecs:
- VBLE Codec (by MarcFD): A huffyuv based encoder discussion.
- LocoCodec (by TheRealMoh): see also here.
- ffvfw codec - has various modes, in particular HuffYUV yv12.
- YV12 resources: Technical explanation of YV12 (and similar formats)
- 'Video Rendering with 8-Bit YUV Formats' - Good Microsoft page on YUV
- 'About YUV Video' - Some other Microsoft stuff
- 4:2:0 Video Pixel Formats - Microsoft