Playing the .mp4sub file format
I have just downloaded a bunch of .mp4 files, which are accompanied by .mp4sub files. If you also wonder, what is this, and what kind of software can be used to play these wideo files, then read on.
Details
There are exactly three .mp4sub (named b, c and d) files for each .mp4 (named a). An example pattern:
a_Astra.mp4,b_Astra.mp4sub,c_Astra.mp4sub,d_Astra.mp4sub.
When I rename any of .mp4sub files into .mp4 extension, I can play this file with any standard video player, and it seems to be a normal FullHD (1920×1080 resolution) video in MP4 codec.
After a bit of research, I managed to find out, that these seems to be Samsung’s 4K / UltraHD demo video files — one 4K / UHD movie split into four files.
Others
Most UHD / 4K video producers uses “standard” approach. They’re encode video in 4096×2304 (FullUHD / Full4K?) or 3840×2160 (UHDReady / 4KReady?) resolution in a standard multimedia container like .mp4 or .mkv. You only need a one file and a standard video player (of course any, that is able to play video in such big resolution) to play such content.
Since entire 4K / UHD movie is stored in one file, you may expect a very large video files (for example, 309 GB file for 48,5 minutes long “TimeScapes” movie) and around 100 MB/s or more bitrate. Of course, these are bitrates, that assumes best viewing experience, because most demo files for 4K / UHD technology shows nature or beautiful views and are maximally focused on details. We may expect, that commercial, theatrical movies will offer much lower bitrate and eventually a much smaller file sizes.
Samsung
Samsung took a different approach. Instead of encoding entire 4K resolution in one video, it split it into four files in FullHD format (4K / UHD is often marketed as four times FullHD)1. These are simply four parts (upper-left, upper-right, lower-left and lower-right) of one movie. To get the entire expression of 4K / UHD movie, yo need a special video player, that will play all for files in the same time, sync together and placed in correct parts of 4K / UHD screen.
Since entire 4K / UHD movie is split into four “standard” FullHD files, neither file size nor bitrate aren’t too overwhelming. An example demo video (one fourth) have 1 GB size for 7,5 minutes long movie and it is encoded with approx. 20-30 MB/s bitrate. Of course, you have to get these numbers times four to get values for entire 4K / UHD movie. Again, I assume, that these are very good quality-oriented bitrates and file sizes (for the reasons explained above). Standard, commercial FullHD movies usually uses lower bitrates and smaller file sizes.
Playing .mp4sub files
My demo movie comes with information, that suggests, that VLC (for both Windows and MacOS), starting from version 2.0.1 is able to play these files correctly. However, I can’t confirm this. My VLC 2.1.5 plays only first (.mp4) file. Maybe it need certain configuration or special codec for this purpose (see below)?
When digging through extra files, that came with my demo movies, I found (again, unconfirmed) information for both Windows and MacOS, about CineForm codec, that may be used to encode 4K / UHD movies.
Windows:
Install the GoPro Cineform Studio. This should install the codecs which will allow you to play back the cinceform AVI with your player of choice – VLC or Windows Media Player.
Mac OSX:
The cineform avi can be played back with quicktime. Copy the quicktime codecs to Macintosh HD > Library > Quicktime
If you are having issues, the H264 will play back in both Quicktime and VLC. We have had better performance using VLC to play back the H264.
That’s all, I managed to discover about .mp4sub files so far.
1 For past few years Samsung is quite well known for “strategy” of “how to make simple things really complex”. This is an example of it.