I recently went to an beautiful forest area with my parents and found an AMAZING area for some cinematic videos. I felt like i took a super cool clip and decided to quick transfer it immediatelly to my phone. All good so far; the video took a long time to copy, but it was like 6 min long and in 4K@30.  
I didn't immediatelly check the full video on my phone, but i did check the low quality video that's atumatically saved... it played fine and i was happy. A few hours later i wanted to show the video to my father and OMG it didn't play on my phone. I even tryied to open it with 3 different players (samsung base player, vlc and one for slow motion i can't remember its name) and nothing. Ok, maybe the file was corrupted during the transfer and i decided to connect the drone again and play it directly from it. Nothing. I literally felt like crying.

All hope wasn't lost; i hadn't tryed playing it on my PC. After a full day in the field, feeling like cr*p because i thought the video was actually lost, i finally got back to my home and checked the video and IT DID PLAY. The day was saved and eveything is fine now. But... i keep wondering why wouldn't the video play o my phone? has anyone had a similar issue before?

Did you download the full video from the MINI II to the cell phone? The original versions is no the full res video so you need to download it. Leave the drone connected as if you were going to fly and go to Fly Me app and look for icon for library on first page....don't go to connect to aircraft. Click on the download arrow icon.  Alternatively you can put your SD card in a computer and play the movie from there. The instructions that come with the MINI II are hit and miss....more good information at DJI web site and how to videos. Also lots of good stuff at Youtube. MAKE sure you upload all the latest firmware updates for the drone and the remote controller there have been a couple just in the last couple of weeks. Also get the latest version of the Fly Me app from DJI. The Android versions at the PLAY STORE lag the updates at DJI itself. Lots of NEW features and bug fixes so very worthwhile updating all when you can. For drone and remote controller you do that from within the Fly Me app.

My first guess is maybe the phone isn't up to it?
Processor and RAM are key especially when trying to play/work with 4k vids....

It sounds to me like Quick Transfer sometimes can have packet loss which is typical for data transfer.  Most of the time there is a verification that each pack of data was sent and is not corrupted.  The case of missing packet or corrupted packet the receiving device requests the packet be sent again.  This is a standard process used across the data transfer spectrum.  Possible DJI did not implement that process in the DJI Fly for Quick Transfer.

Mobile devices in particular can have issues processing high resolution video and downscaling it to the appropriate mobile format.  There is a misconception that mobile devices can play true 4K.  The reality the 4k format pixel density and size format are not compatible with mobile screen sizes.

Often you see this issue commented on by people who downloaded a video on Youtube and wonder why when transferred to a computer the 4K video downloaded no the mobile device has poor quality.  Most phones store a high resolution video shot from the internal camera and then scale it to the mobile devices size when viewed.  This is an integral process that is typically limited to video shot on the built in camera.

Astro Bob Posted at 1-27 13:09
Did you download the full video from the MINI II to the cell phone? The original versions is no the full res video so you need to download it. Leave the drone connected as if you were going to fly and go to Fly Me app and look for icon for library on first page....don't go to connect to aircraft. Click on the download arrow icon.  Alternatively you can put your SD card in a computer and play the movie from there. The instructions that come with the MINI II are hit and miss....more good information at DJI web site and how to videos. Also lots of good stuff at Youtube. MAKE sure you upload all the latest firmware updates for the drone and the remote controller there have been a couple just in the last couple of weeks. Also get the latest version of the Fly Me app from DJI. The Android versions at the PLAY STORE lag the updates at DJI itself. Lots of NEW features and bug fixes so very worthwhile updating all when you can. For drone and remote controller you do that from within the Fly Me app.

Hi. Yes, i did all you said. At first I used Quick Trasnfer as I didn't had my microSD card reader on me. When the video didn't play, i actually tryed reading the microSD on the phone first and as it didn't work i then tryed turning the drone on and play it from the aircraft without transfering or anything. And i do have the latest verion of the DJI app (downloaded the apk directly from DJI website instead of waiting for it to be available in the playstore)

JohnLietzke Posted at 1-27 14:37
It sounds to me like Quick Transfer sometimes can have packet loss which is typical for data transfer.  Most of the time there is a verification that each pack of data was sent and is not corrupted.  The case of missing packet or corrupted packet the receiving device requests the packet be sent again.  This is a standard process used across the data transfer spectrum.  Possible DJI did not implement that process in the DJI Fly for Quick Transfer.

Mobile devices in particular can have issues processing high resolution video and downscaling it to the appropriate mobile format.  There is a misconception that mobile devices can play true 4K.  The reality the 4k format pixel density and size format are not compatible with mobile screen sizes.

Well, maybe that's the reason. I normally run a Galaxy S9 on a daily basis, but that day i had left that phone somewhere and was using a galaxy A30, which is ok to fly but i do notice it's less potent (in terms of processing speed and everythin) than the S9.

BORRERO.MD Posted at 1-28 04:35
Well, maybe that's the reason. I normally run a Galaxy S9 on a daily basis, but that day i had left that phone somewhere and was using a galaxy A30, which is ok to fly but i do notice it's less potent (in terms of processing speed and everythin) than the S9.

I believe the phone just was hanging, thats all.

BORRERO.MD Posted at 1-28 04:35
Well, maybe that's the reason. I normally run a Galaxy S9 on a daily basis, but that day i had left that phone somewhere and was using a galaxy A30, which is ok to fly but i do notice it's less potent (in terms of processing speed and everythin) than the S9.

The lack of power on the phone could be the issue.  

Did you stop recording before switching-off the drone?

How much free space do you have on the phone? Since I know that some phones hate getting low on free space, since some phones use for more than just storage.

BORRERO.MD Posted at 1-28 04:35
Well, maybe that's the reason. I normally run a Galaxy S9 on a daily basis, but that day i had left that phone somewhere and was using a galaxy A30, which is ok to fly but i do notice it's less potent (in terms of processing speed and everythin) than the S9.

From just looking at the specs of those 2 phones the A30 will only handle 1080P but the S9 will do 4k