Open with the document App, only the file name and file type will be displayed, and the general video can be played directly. So, I switched to AVplayer to play this video with only sound but no picture. mp4info: File: major brand: mp42 minor version: 0 compatible brand: mp42 compatible brand: mp41 fast start: yes Movie: duration: 18842880 (media timescale units) duration: 209365 (ms) time scale: 90000 fragments: no Found 2 Tracks Track 1: flags: 1 ENABLED id: 1 type: Video duration: 209320 ms language: eng media: sample count: 5233 timescale: 25000 duration: 5233000 (media timescale units) duration: 209320 (ms) bitrate (computed): 9592.363 Kbps display width: 1920.000000 display height: 1080.000000 frame rate (computed): 25.000 Sample Description 0 Coding: avc1 (H.264) Codec String: avc1.640029 AVC Profile: 100 (High) AVC Profile Compat: 0 AVC Level: 41 AVC NALU Length Size: 4 AVC SPS: [67640029ac2ca501e0111f7350101014000003000400000300ca10] AVC PPS: [68e881135250] Width: 1920 Height: 1080 Depth: 24 Track 2: flags: 1 ENABLED id: 2 type: Audio duration: 209320 ms language: eng media: sample count: 9814 timescale: 48000 duration: 10049536 (media timescale units) duration: 209365 (ms) bitrate (computed): 317.376 Kbps Sample Description 0 Coding: mp4a (MPEG-4 Audio) Codec String: mp4a.40.2 Stream Type: Audio Object Type: MPEG-4 Audio Max Bitrate: 407250 Avg Bitrate: 317375 Buffer Size: 1536 MPEG-4 Audio Object Type: 2 (AAC Low Complexity) MPEG-4 Audio Decoder Config: Sampling Frequency: 48000 Channels: 2 Sample Rate: 48000 Sample Size: 16 Channels: 2 I used the video conversion tool to convert it to fit the iPhone： File: major brand: isom minor version: 200 compatible brand: isom compatible brand: iso2 compatible brand: avc1 compatible brand: mp41 fast start: yes Movie: duration: 209320 (media timescale units) duration: 209320 (ms) time scale: 1000 fragments: no Found 2 Tracks Track 1: flags: 3 ENABLED IN-MOVIE id: 1 type: Video duration: 209320 ms language: eng media: sample count: 5233 timescale: 12800 duration: 2679296 (media timescale units) duration: 209320 (ms) bitrate (computed): 11996.339 Kbps display width: 1920.000000 display height: 1080.000000 frame rate (computed): 25.000 Sample Description 0 Coding: avc1 (H.264) Codec String: avc1.640033 AVC Profile: 100 (High) AVC Profile Compat: 0 AVC Level: 51 AVC NALU Length Size: 4 AVC SPS: [27640033ac1316c0780227e5c05a8080809818002ee0000bb82f7be0f8442370] AVC PPS: [28ee1f2c] Width: 1920 Height: 1080 Depth: 24 Track 2: flags: 3 ENABLED IN-MOVIE id: 2 type: Audio duration: 209320 ms language: eng media: sample count: 9812 timescale: 48000 duration: 10047360 (media timescale units) duration: 209320 (ms) bitrate (computed): 317.379 Kbps Sample Description 0 Coding: mp4a (MPEG-4 Audio) Codec String: mp4a.40.2 Stream Type: Audio Object Type: MPEG-4 Audio Max Bitrate: 317379 Avg Bitrate: 317379 Buffer Size: 0 MPEG-4 Audio Object Type: 2 (AAC Low Complexity) MPEG-4 Audio Decoder Config: Sampling Frequency: 48000 Channels: 2 Sample Rate: 48000 Sample Size: 16 Channels: 2 The AVC Level and bitrate both higher than the first video, but it plays normally。 So why can't the first video play? I want to know which MP4 videos the iPhone can't play. Apple doesn't have specific specs, but says it supports MP4 and H.264

At present,i set "User Interface Style" Light in Info.plist