```bash
# convert with default settings
ffmpeg -i input.mkv output.mp4

# convert to mp4 using nvidia nvenc
# where -b:v is suitably set, e.g 2M for 720p
ffmpeg -i input.mkv -c:v h264_nvenc -b:v 4M output.mp4
# as above but don't re-encode audio
ffmpeg -i input.mkv -c:v h264_nvenc -b:v 4M -c:a copy out.mp4  

# extract audio as wav
ffmpeg -i input.mp4 output.wav

# extract aac audio from mp4
ffmpeg -i input.mp4 -vn -c:a copy output.m4a

# don't reencode anything (just change metadata or container format)
ffmpeg -i input.mp4 -c copy output.webm

# don't reencode audio, but scale video
ffmpeg -i input.mp4 -c:a copy -vf scale=w=1280:h=720 output.mp4
```

## Metadata
```bash
# extract metadata
ffmpeg -i input.mp4 -f ffmetadata metadata.txt      # writes metadata to metadata.txt

# applying metadata
ffmpeg -i input.mp4 -f ffmetadata -i metadata.txt -map_metadata 1 ...other_opts... output.mp4

# specifying metadata
ffmpeg -i input.mp4 -metadata artist="Mr Flibble" -metadata title="Hex Vision" -c copy output.mp4
```

## Loop Static Image
From [stackoverflow](https://stackoverflow.com/questions/25891342/creating-a-video-from-a-single-image-for-a-specific-duration-in-ffmpeg)
```bash
ffmpeg -loop 1 -i image.png -c:v libx264 -t 15 -pix_fmt yuv420p -vf scale=320:240 out.mp4
```
* The -t 15 makes it 15 seconds long.
* The -vf scale=320:240 sets the width/height.

## Audio Filters
A 200Hz highpass filter
```
ffmpeg -i in.wav -af highpass=f=200 out.wav
```