Tap Decoder in the More menu in the upper right corner of the screen.
You may choose a decoder (QuickTime, Hardware, Software) you would like to configure.
It is played first with the hardware decoder if the video has a codec which can be decoded with hardware decoder like below.
– supported on iOS11 or later on devices with Apple A9 or later
* H.264 Hi10P(High 10 Profile)
– supported on iOS10 or later on devices with Apple A9 or later
Software decoding uses CPU, so playback performance may vary depending on CPU performance. And CPU usage is higher than hardware decoding, which may increase battery drain.