How would I change the exposure of a series of images with ffmpeg while compiling into an MP4, please give a command line example.
To change the exposure of a series of images using ffmpeg, you can use the curves filter. This filter allows you to adjust the brightness and contrast of an image.

Here is an example command that changes the exposure of a series of images and compiles them into an MP4:
``` 
ffmpeg -i image-%d.png -vf curves=levels=0:0.5:1 -c:v libx264 -pix_fmt yuv420p output.mp4
``` 
In this command:

- image-%d.png specifies the input images, where %d is a placeholder for the frame number.
- curves=levels=0:0.5:1 specifies the curves filter and sets the exposure to 0.5. The levels parameter takes three values: the minimum input level, the middle level, and the maximum input level. In this example, 0:0.5:1 means that the minimum input level is 0, the middle level is 0.5, and the maximum input level is 1.
- libx264 specifies the H.264 video codec to be used for encoding the output video.
- yuv420p specifies the pixel format for the output video.
- output.mp4 is the name of the output file.

Note that this is just one example, and you can adjust the exposure further by changing the values in the curves filter.
Can you rewrite this, but with AV1 encoding and outputting to a .MKV file instead?
Certainly! Here is an example command that changes the exposure of a series of images using ffmpeg, encodes the output using the AV1 video codec, and saves the output as an MKV file:
```
ffmpeg -i image-%d.png -vf curves=levels=0:0.5:1 -c:v libaom-av1 -pix_fmt yuv420p output.mkv
```
In this command, the -c:v option specifies the video codec to be used for encoding the output video. Instead of libx264, we're using libaom-av1, which is the AV1 codec.

The -pix_fmt option specifies the pixel format for the output video, which is set to yuv420p in this example.

Finally, the output file is named output.mkv, which saves the output as an MKV file instead of an MP4 file.