: Alpha Plus Movie is a movie file that can simultaneously process alpha composition and additive composition in one drawing.
The conventional alpha composition has the disadvantage that the silhouette edges become black due to the optical effect.
In the Alpha Plus Movie, both the drawing of characters by alpha composition and the optical effect by additive composition are compatible.
The size of this movie file is the same as a normal alpha movie. As the alpha composition and additive composition are processed at the same time in one drawing, the drawing load is the same as that of a normal movie.

Alpha Plus Movies can be encoded with the "Sofdec2 Encoder command line version".
(* Sofdec2 Encoding Wizard (GUI version) will be supported in the future.)
The following describes how to create Materials.

(1) Preparing Materials

In order to create the Alpha Plus Movie, you need to prepare the following two video materials:

Video material for color information including additive composition
Video material for alpha composition

Below will use After Effects as an example to explain how to prepare two types of materials:

(a) Video material for color information including additive composition

: Render "including" the effect you want added to the composition.
Set the "Channel" field to "RGB" in the output module settings of the "Render Cue" to render.

(b) Video material for alpha composition

: Render "excluding" the effect you want added to the composition.
Set the "Channel" filed to "RGB + alpha" in the output module settings of the Render Cue to render.
Set the "Color" field to "Composite channel (with mattes)".

(2) Encode

: "Sofdec2 Encoding Wizard" (GUI version) does not support Alpha Plus Movie encoding yet. Please use Sofdec2 Encoder command line version instead.
Then create the following batch file.
A batch file can be generated by selecting "Export" -> "Batch file (New)" in the "Sofdec2 Encoding Wizard" (GUI version) menu. Set the alpha movie with the normal encode settings and export the batch file. This will output a file that is almost identical to the batch file shown below. You can use this as the template.

sofdec2enc.exe -video00=".\AlphaPlus_RGB.avi" -alpha00=".\AlphaPlus_Alpha.avi" -scale=256,256 -framerate=29.97 -bitrate=2000000 -output=".\SAYA_AlphaPlus.usm" -work_dir="." -preview=OFF -gop_closed=on -gop_i=1 -gop_p=4 -gop_b=2

: Specify "(a) Video material for color information including additive composition" for the option -video00= .
Specify "(b) Video material for alpha composition" for the option -alpha00= .
Note that -output and -work_dir are the output-related settings and need to be set.
-scale refers the resolution after encoding. To resize, please specify here.
Change -bitrate according to the target image quality.
Do not change the options under -preview.

[Remarks]

When creating Alpha Plus Movie, the average bit rate is about twice that of no alpha.
1. Basically, it will try to encode by assigning 60% of the display bit rate value of user specification or automatic setting to the RGB part and 40% to the alpha part.
2. In the automatic setting of H.264/VP9, try to encode by allocating the bit rate assuming H.264/VP9 codec for RGB part and Sofdec.Prime codec for alpha part.
  
  （The allocation is different from the case specified by the user)
3. For the final compression ratio of the alpha part, adjust the image quality using "alpha_quality" option of the command line tool.
The created Alpha Plus Movie can be previewed using Sofdec2 Viewer .

From the Sofdec2 Viewer menu, check View -> Blend Mode -> Additive .
Also, change the View -> Background according to the contents and check the transparency.
Currently, the checkbox for alpha movie with video codec: H.264, VP9 is not enabled in the wizard version. Please create with the command line version.

(3) Playback

: For the drawing method when playing the Alpha Plus Movie, refer to the sample program "Alpha Plus Movie". (Some platforms are not included)