Seeking in video failed Operation not permitted, will use first frame

```
$ ffmpegthumbnailer -v
ffmpegthumbnailer version: 2.2.0

$ ffmpegthumbnailer -i 1.mp4 -o 1.mp4.png -c png -s 300 -t 00:00:02
Seeking in video failed Operation not permitted, will use first frame.

$ ffmpeg -ss 00:00:02 -i _/1.mp4 -vframes 1 _/1.mp4.png
<succeeds>
```

[1.mp4.gz](https://github.com/dirkvdb/ffmpegthumbnailer/files/1975519/1.mp4.gz)