I found that ffplay.exe in the downloaded file of ffmpeg, which is famous for video editing, can be a powerful 3D video player, but because it is a console application, it is not very easy to use. Therefore, i created 3Dffplay, a GUI-based application that simplifies the 3D-related settings of ffplay.exe. Store 3Dffplay.exe and ffplay.exe in the same folder and start 3Dffplay.exe. In the menu settings, specify the input stereo format and output stereo format, then drag and drop the 3D video or still image you want to play and it will start playing. The player supports most stereo formats and has a fairly high playback performance. During playback, you can also use the keyboard or mouse to view the full screen, pause the video, adjust the volume, etc.

3dffplay010.zip 3DFFPlay Ver0.1 2023/2/6 21kbyte

Download of ffplay.exe
The official FFmpeg page only distributes the source code.
Press the Download button to download the file built as a Windows executable.
Download button -> Get packages & executable files(Windows) -> Windows builds by BtbN -> Latest Auto-Build -> ffmpeg-master-latest-win64-gpl.zip

1.Download "ffmpeg-master-latest-win64-gpl.zip" from the website mentioned above and unzip it.
2.In the extracted folder, there is a folder called "bin", in which you will find ffplay.exe, so store it in the same folder as 3dffplay.exe.

How to use
1. Launch 3dffplay.exe and the following screen will appear.

The current settings are displayed in the area framed in red.
Keyboard and mouse operation methods on the player screen are displayed in the area surrounded by a blue frame.

1. Menu -> File ->Setting

・Launch in full screen : If checked, the player starts in full screen mode.
・Play Original Video : If checked, ignores 3D input/output settings and simply plays the specified file.
・Set stereoscopic image format of input : Select the 3D format of the input file from the drop-down list
・Set stereoscopic image format of output : Select the 3D format to play from the drop-down list
・Error check mode : If checked, the command prompt displays the execution status of ffplay.exe. If you have a problem when it does not play, checking here will help you to understand the cause to some extent.

2.Drag-and-drop video playback
When a media file (movie or still image) is drag and drop onto the 3Dffplay.exe startup screen, the player starts and plays it back under the conditions you set. If another media file is drag and drop onto the 3Dffplay.exe screen (not the playback screen) during playback, the video will switch to a new video. To end playback, use the close button in the upper right corner of the playback screen, or press the ESC key or the Q key during full-screen playback.

3.Video playback from menu
File -> Open

Select the video you want to play, set the 3D format, etc., and press the Open button to start the player, which will play the video under the conditions you set.

Advantages of ffplay.exe
・Wide variety of video formats supported, including H265 MP4 video playback
・High playback performance -> may be usable on low-spec PCs

3D-related explanation links for ffplay (ffmpeg)

Known Problems
3Dffplay.exe only launches a video player called ffplay.exe, so it cannot handle ffplay.exe problems. The following problems with ffplay.exe are known at this time

1. If Set stereoscopic image format of output is set to interleaved rows, the display width will be half of the expected value.
The interleaved output must be displayed in the original video size to be displayed correctly.

2. Half SBS display in full screen for 3DTV is centered.

For 3DTV, We want it to be displayed as shown below.

3. The full screen display is always displayed on the primary monitor, even if it is started from a sub-monitor.  
When using in a multiple monitor environment, the screen you wish to display must be set as the primary.