Removed video information in thumbnails after cutting a fragment

Hi everybody,

As a Shotcut user, I am here to describe a weird situation that I have found several times when I use this software. Because it is something pretty uncommon, I will try to do my best to describe it using an example. Sorry if my English is a bit rusty. It is not my mother tongue.

Let’s imagine that we have a videoclip. That videoclip has two scenes, one after the other. The first scene is a red scene (the color is to simplify the explanation). The second scene is a green one.

Now, we want to remove the red fragment so, using the tool named “cutter”, we cut the videoclip in two parts. The cut is done exactly at the point where the red scene finishes and the green scene starts. Then, I remove the red fragment. Great! Now we only have the green videoclip. So, we export it.

When we play the exported file, we can see only the green fragment. But, and here it is when the problem sometimes appears, the videoclip thumbnail contains the last fotogram of the red fragment. But that fotogram never appears when we play the movie file. It is like a kind of remains of information that is not played but it is inside the file, and it is used by the software responsible for creating the video thumbnail. More expecifically, I have seen this problem in Whatsapp, when I am checking the video library or when the video is sent to someone and the thumbnail appears in the conversation.

It is important to remark that I am not capable of replicating the problem when I want. The problem appears when it wants. Indeed, I have found it three or four times during the last two years.

System: I am using the Shotcut version 21.12.24, but I have seen this problem in previous versions. My OS is Windows 10 Pro 21H2. My system is i7-10510, 16GB and a 512 GB NVMe.


Is it possible that when you Split (cut) the clip, you leave one red frame in the green clip?

In the timeline,the clip would show a red thumbnail at the start and a green one at the end. And that single red frame might not be visible when playing the clip in the preview or when you play the exported clip. Especially if you use a high frame rate, like 60 fps for example.

Hi MusicalBox, thank you for answering.

It is the only explanation that I can figure. Maybe I am making a mistake when I cut the scene and that “volatile” frame (I wrote “fotogram”… sorry, frame is “fotograma” in Spanish) is there, in the final videoclip.


2 demonstrations:

1- Moving the playhead from left to right and cutting as soon as the preview displays a green frame


Result = 2 green thumbnails

2- Moving the playhead from right to left and cutting as soon as the preview displays a red frame

Result One red thumbnail, one green thumbnail.

That unexpected frame might appear only as one frame at the beginning of the file that you do not notice when the player automatically starts playback. Open the video in Shotcut and seek to the beginning of the file to see if there is an unexpected frame. If you are seeing it, then you need to verify if was a mistake in the Shotcut project. If not an editing mistake, then Shotcut is struggling to have frame accurate seeking on your video file and it needs to be converted in Properties to something frame accurate.

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