Video compositing with Natron

Surfers

Currently, Merge1 blends the video with uniform speed. If you want to make the overlay quick in the first 25 frames and then you want it to go slower, click on the wavy line symbol and select Show in curve editor . Natron should now switch to the Curve Editor in the lower left pane.

The diagram here visualizes how the regulator changes the Mix over time. Time is plotted from left to right. The scale with the frame numbers can be found on the bottom edge. The vertical red line marks the beginning of the video. The orange line marks the position that is currently displayed in the preview.

To the right, next to frame 100, is a blue point as well as the second keyframe. The sloping line graphically displays how the Mix regulator changes: On the first keyframe, Mix is set to 1 , on the right-hand one, it's set to 0 , and the line falls uniformly henceforth. Natron selects the color of the line randomly, and it happens to be blue in Figure 7.

Figure 7: You can determine the relative effect in the Curve Editor.

Now, you can not only move the keyframes by dragging and dropping them within the Curve Editor , you can also change the shape of the line. To do this, click on any of the two keyframes. Two white squares should appear the left and right of the selected key. If you drag either of them with your mouse, you can change the slope of the curve (Figure 8).

Figure 8: You can change the slope of the line and thus the control of the effect by using the white dots.

Currently, this process is a bit fiddly because the Mix regulator only allows for values between 0 and 1 despite the fact that Natron would definitely like to display values up to 50. Nonetheless, you may zoom in the pane with the mouse wheel. Natron then travels to the point you aim at with the mouse pointer. Unfortunately, there is no scroll bar in Natron 1.0.0 yet, so you will have to zoom in and out to change positions.

The blue line is straight by default. If you only drag one of the white points, you will only change your control. On the other hand, if you select and change multiple white points, the line will depict a curve. You can configure the transition to start fast and then slow down (or vice versa).

You can also display and change the curve for all other effects that use keyframes. Note that using the right mouse button, you can select different interpolation techniques in the Curve Editor under Interpolation .

Packaging

You must be able to render the final scene out of Natron. You can use nodes for this process, too. Switch over to the NodeGraph tab, click on the drawing surface with the right mouse button, and select Image | Writers | WriteFFmpeg . In the window that appears, select the file format at the lower left; for example, select mp4 for a film in MPEG4 file format. Note that this only pertains to the file format and not the compression format.

Assign a file name to the right next to Sequence and click on Save . This creates the new node WriteFFmpeg1 , which you can connect to the output of the Merge1 node. Outputs can be attached to multiple nodes. These will then preserve the same data.

If you click on Render in the settings on the right-hand side of the control, the WriteFFmpeg1 node will write the obtained video first only in a file. Beforehand, you should correctly set the Format . Natron does not currently offer pre-settings, so users must be well versed in the desired compression procedure.

For MPEG4 video, select MP4 , expand the Advanced tab, and select Codec for MPEG-4 part 2 (Figure 9). Once all of the settings are correct, click on Render . If you want to save only a single image on your hard disk, you can use the Image | Write node, load the reversed image, and send it to its output. New nodes can be generated by means other than just using the right mouse button. All nodes can also be found behind the honeycomb-shaped icons on the left side of the window. To delete a new node, select it and then simply press the delete key. See the "What's in a Name?" box for information on naming nodes.

Figure 9: With these settings, the WriteFFmpeg1 node produces a video in MP4 format.