Add fade to black transition to MP4 video #

3 methods, from least to most efficient. Original MP4 video clip ≈ 2.4MB.

iMovie 10.1.2:
1. File > New Movie...
2. Drag MP4 video into project
3. Window > Content Library > Transitions
4. Click and drag Fade to Black transition to end of video
5. File > Share > File...
6. At the lowest resolution and quality settings, the resulting MP4 was ≈ 12.5MB
ScreenFlow 5.0.6:
1. File > New > New Document
2. Set custom width and height to match existing MP4 file
3. Insert > Choose... > select MP4 file
4. Highlight imported video clip
5. Edit > Add Ending Transition
6. File > Export...
7. With no scaling and using the "Web - Low" preset, the resulting MP4 was ≈ 2.7MB
ffmpeg 2.6.2:
1. Open original MP4 in QuickTime
2. Navigate to end of video and change time display to Frame Number, noting the number displayed (e.g., 927)
3. $ ffmpeg -i in.mp4 -vf "fade=out:900:27" -acodec copy out.mp4
4. Resulting MP4 was ≈ 2.1MB (yes, smaller than the original!)

Thanks to LordNeckbeard's tip and link to FFmpeg's fade filter documentation.

UPDATE:

Add fade in and fade out:

$ ffmpeg -i in.mp4 -vf "fade=in:0:10,fade=out:900:27" -acodec copy out.mp4

$ cat mp4s.txt 
file '/path/to/1.mp4'
file '/path/to/2.mp4'
file '/path/to/3.mp4'

$ ffmpeg -f concat -safe 0 -i mp4s.txt -c copy out.mp4

/mac | Nov 24, 2016