Blender is a widely used open source application for 3D modeling and animation. A perhaps not so well known feature of blender is its ability to edit video and audio, thanks to its sequence editor. In fact, it is a full blown non-linear editing module, which allows to apply numerous effects, as well as doing simple tasks as blending clips together, adding transitions, etc.
I have been using it recently to do some basic video editing, and I think it keeps up quite well in comparison with other, more “professional”, video editing tools. Since blender has its own unique interface, which doesn’t follow the conventions adopted by other programs (it is heavily optimized for a keystroke-oriented workflow), it might be a little bit difficult at the beginning, but once you learn the basic elements of the interface, is in fact very intuitive. Here you have two pages at BlenderWiki with detailed information about the sequence editor in blender:
This blog post is also a very useful reference on this topic:
Simple clip mixing
I just want to add some brief comments about the task of creating simple videos by mixing short clips, adding titles and transition effects (all of this can be found in the VSE manual linked above).
First of all, there is a predefined layout for video editing, which can be selected by going to the top menu and choosing SR:4-Sequence in the layout list (the default being SR:2-Model). This layout has a timeline, an IPO curve editor and a preview window.
In order to render the videos, you have to select the “Do sequence” option right below the ANIM button in the Scene (F10) menu. The output file(s) will created in the directory set in the first box of the output group. By default, blender will render each frame into a separate jpg file, but the output could also be an avi file. To do this, you chose “AVI codec” in the drop-down list of the format group. In this case, the name of the output avi file will be taken from the text entered in the output box. For instance, if it says “C:\Users\Render\test” the output file will be named test0001-0250.avi and created in C:\Users\Render. 0001-0250 reflects the frame range, which of course can be also modified by just entering the desired values for the start and end frames of the animation.
A simple editing task consists in creating a fade-out/fade-in transition between two clips. This is achieved by using two effects in conjunction: color generator and gamma cross. If we want to do a fade-out to black, we add a color generator by going to “Add|Effect|Color Generator” (in the video sequence editor window). The default color of the color generator is gray, but is easily changed by opening its properties by selecting it and pressing “N”. Then we add a gamma cross between the video clip and the color generator. In order to do this, we have to select both the clip and the color generator (shift key + right mouse button on each), but in that order: first the clip and second the color generator. Once they are selected, we add the gamma cross (“Add|Effect|Gamma Cross”). This generates the fade-out. The fade-in is created in the same way, but selecting first the color generator and then the video clip.
Sound can also be edited in the VSE. In order to render a sound file from the sequence editor, go to Scene(F10) -> Sound block buttons -> MIXDOWN. This will create a wav file using the same convention as for avi files. If the video is rendered to avi after generating the wav, then the wav will be added as an audio track to the avi.
To control the volume of an audio strip, add an IPO curve in the IPO curve editor for the selected audio strip, by pressing ctrl key + left mouse button inside the IPO curve editor window. Tab key switches between curve and point editing, and the “i” key inserts a new control point at current frame location. By changing the height of the IPO curve between 0 and 1, the volume changes between silence and the maximum.
Audio and video can also be mixed with an external program such as avidemux. In such a case, the video has to be rendered without the audio track. This is achieved just by deleting the wav file in the case it has been created before and then rendering the sequence again by pressing the ANIM button.