prompter: How would I change the exposure of a series of images with ffmpeg while compiling into an MP4, please give a command line example.

assistant: 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.

prompter: Can you rewrite this, but with AV1 encoding and outputting to a .MKV file instead?

assistant: 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.

assistant: Here's the modified command using AV1 encoding and outputting to a .MKV file:

```bash
ffmpeg -i image-%d.png -vf "curves=levels=0:0.5:1" -c:v libaom-av1 -strict experimental -crf 30 -b:v 0 -pix_fmt yuv420p output.mkv
```

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.
* libaom-av1 specifies the AV1 video codec to be used for encoding the output video.
* strict experimental is required for using the AV1 codec.
* crf 30 sets the Constant Rate Factor (CRF) to 30, which determines the quality of the output video. Lower values result in better quality but larger file sizes. You can adjust this value to your preference.
* b:v 0 sets the target bitrate to 0, meaning the encoder will use the CRF value instead to determine video quality.
* yuv420p specifies the pixel format for the output video.
* output.mkv is the name of the output file in the MKV format.

Keep in mind that encoding with AV1 can be slower compared to other codecs like H.264 (libx264). You can adjust the CRF value and other parameters to achieve the desired balance between quality and encoding time.

assistant: To do this, you can use the eq filter to adjust the brightness. Here's a command-line example:

    ffmpeg -r 24 -pattern_type glob -i 'input_files_*.jpg' -vf "eq=brightness=0.1:saturation=1" -c:v libx264 -pix_fmt yuv420p -crf 23 output.mp4

Replace input_files_*.jpg with the appropriate pattern for your image files. This command assumes that your images are in the JPEG format. Change the file extension to match the image format you're using.

prompter: Can you provide an explanation for each of the command line arguments in your answer ?

assistant: Sure! Here's an explanation for each argument:
- `-r 24` sets the video's framerate to 24 FPS
- `pattern_type glob` sets ffmpeg to look for files with the glob pattern type
- `-i 'input_files_*.jpg'` tells ffmpeg to use files named 'input_files_' with the frame number appended to it.
- `-vf "eq=brightness=0.1:saturation=1"` tells ffmpeg to set the brightness 10% higher and set the saturation higher.
- `-c:v libx264` tells ffmpeg to encode in the H.264 (MP4) file format.
- `-pix_fmt yuv420p` sets the color format to yuv420p
- `-crf 23` sets the video's lossiness during encoding, which should be a number from 0 to 51. 
- finally, `output.mp4` sets the filename of the resulting video.

Many of these values can be customized to fit your needs better.

assistant: Certainly! The ffmpeg command provided includes several arguments, each of which has a specific function. Here's an explanation for each of the arguments:

-r 24: This argument specifies the frame rate (frames per second) for the output video. In this case, it is set to 24 frames per second.
-pattern_type glob: This argument specifies the pattern type to be used for the input file sequence. The glob pattern type allows for the use of shell-style wildcards in the file sequence specification.
-i 'input_files_*.jpg': This argument specifies the input files to be processed by ffmpeg. In this case, it's a file sequence of JPEG images whose filenames match the pattern input_files_*.jpg. The * is a wildcard that matches any string of characters.
-vf "eq=brightness=0.1:saturation=1": This argument specifies a video filter (-vf) to be applied to the input video stream. In this case, the eq filter is used to adjust the brightness and saturation of the video. The brightness=0.1 parameter increases the brightness by 0.1, and the saturation=1 parameter sets the saturation to its default value (no change).
-c:v libx264: This argument specifies the video codec (-c:v) to be used for encoding the output video. In this case, the libx264 codec is used, which produces H.264 video.
-pix_fmt yuv420p: This argument specifies the pixel format (-pix_fmt) to be used for the output video. In this case, the yuv420p pixel format is used, which is a common format for H.264 video encoding.
-crf 23: This argument specifies the constant rate factor (-crf) to be used for video encoding. The CRF value controls the trade-off between video quality and file size, with lower values resulting in higher quality and larger file sizes. In this case, a CRF value of 23 is used, which is a common default value for the libx264 encoder.
output.mp4: This specifies the name of the output video file, which will be saved in MP4 format.
Overall, this ffmpeg command converts a sequence of JPEG images into an H.264-encoded MP4 video with a frame rate of 24 fps, increased brightness, and default saturation. The output video is saved as output.mp4.