TrialPad can import and play almost all audio and videos that are compatible with the iPad. If you are having issues with the compatibility of a video file you can use the free Handbrake desktop program which is available for macOS and Windows (https://handbrake.fr) to convert the video into a compatible format. It has various presets to make the conversion process easy, with the Apple 1080p30 Surround option being a good choice for most situations (see attached screenshot).
If you’re viewing the video in the Dropbox app on your iPad, and it plays back without an issue, it still may not be in a compatible file format to work on the iPad. The reason for this is that Dropbox transcodes the video as it’s being streamed to make it viewable on any device. If you access Dropbox from within TrialPad you will only see the compatible file types.
For those that want specifics, the video formats supported by the iPad are:
H.264 video up to 4K, 30 frames per second, High Profile level 4.2 with AAC‑LC audio up to 160 Kbps, 48kHz, stereo audio or Dolby Audio up to 1008 Kbps, 48kHz, stereo or multichannel audio, in .m4v, .mp4, and .mov file formats; MPEG‑4 video up to 2.5 Mbps, 640 by 480 pixels, 30 frames per second, Simple Profile with AAC‑LC audio up to 160 Kbps per channel, 48kHz, stereo audio or Dolby Audio up to 1008 Kbps, 48kHz, stereo or multichannel audio, in .m4v, .mp4, and .mov file formats; Motion JPEG (M‑JPEG) up to 35 Mbps, 1280 by 720 pixels, 30 frames per second, audio in ulaw, PCM stereo audio in .avi file format