Which iPad model do you own, iPad has very strict limitation on the video codec, video resolution, video bit rate, video frame rate and audio codec, audio bit rate, audio sample rate and audio channels on the file formats played on it, if the MP4 files does not meet the following standard, you will not have a smooth video playback experience:
Video formats requirements:
- 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
Audio formats requirements:
AAC (8 to 320 Kbps), Protected AAC (from iTunes Store), HE-AAC, MP3 (8 to 320 Kbps), MP3 VBR, Dolby Digital (AC-3), Dolby Digital Plus (E-AC-3), Audible (formats 2, 3, 4, Audible Enhanced Audio, AAX, and AAX+), Apple Lossless, AIFF, and WAV