feat(ffmpeg): add changing volume example

Author: ShellTux

content/posts/ffmpeg.md

@@ -48,6 +48,7 @@ Any of the following global options can be seen in the [ffmpeg manpage](https://
 | Rotating a video (transpose=0,1,2,3 1=90º)                   | `ffmpeg -i input.mp4 -vf "transpose=1" rotated.mp4`                                                                                                               |
 | Creating a video thumbnail (@ 3 seconds)                     | `ffmpeg -i input.mp4 -ss 00:03:00 -vframes 1 thumbnail.jpg`                                                                                                       |
 | Extracting Audio Channels                                    | `ffmpeg -i input.mp4 -map_channel 0.1.0 audio_channel.wav`                                                                                                        |
+| Changing Volume (80% Volume)                                 | `ffmpeg -i input.mp4 -filter:a "volume=0.80" output-80-volume.mp4`                                                                                                |
 | Creating a Video Loop (10min=600s loop)                      | `ffmpeg -stream_loop -1 -i input.mp4 -c copy -fflags +genpts -t 600 loop.mp4`                                                                                     |
 | Adding a Video Overlay (Between 0-20s @-10,10)               | `ffmpeg -i main.mp4 -i overlay.mp4 -filter_complex "[0:v][1:v] overlay=main_w-overlay_w-10:10:enable='between(t,0,20)'" -pix_fmt yuv420p -c:a copy overlayed.mp4` |
 | Creating a Picture-in-Picture Effects (Between 0-20s @25,25) | `ffmpeg -i main.mp4 -i pip.mp4 -filter_complex "[0:v][1:v] overlay=25:25:enable='between(t,0,20)'" -pix_fmt yuv420p -c:a copy output-pip.mp4`                     |