Error Concatenating Two Parts of Different Speeds in FFmpeg
When working with video files in FFmpeg, it is common to encounter the need to concatenate different parts of a video. However, when the parts have different speeds, the concatenation process can become challenging. In this article, we will discuss the issue of concatenating two parts of a video with different speeds in FFmpeg, providing a detailed context of the topic and covering the key concepts involved.
Concatenating Parts of a Video
Concatenating parts of a video in FFmpeg is typically done using the concat filter. This filter takes a list of inputs and combines them into a single output. However, when the parts of the video have different speeds, simply concatenating them will result in an output that has a varying speed, which is often not desirable.
Speed Differences in Video Files
Speed differences in video files can occur for a variety of reasons. For example, one part of the video may have been recorded at a slower frame rate than another part. Alternatively, one part of the video may have been sped up or slowed down during editing. In either case, the result is a video that has different speeds in different parts.
Concatenating Parts with Different Speeds
When concatenating parts of a video with different speeds in FFmpeg, it is important to ensure that the output has a consistent speed throughout. This can be done using the setpts filter, which allows you to adjust the presentation timestamp of the input video. By setting the presentation timestamp of each input to the same value, you can ensure that the output has a consistent speed.
Example: Concatenating Two Parts of a Video with Different Speeds
Consider the following example, where we want to concatenate two parts of a video, one with a speed of 20x and the other with a normal speed:
ffmpeg -i 7.mp4 -filter_complex "[0:v]select=between(t,0,9),setpts=PTS-START" output.mp4
In this example, we are using the select filter to select the first 9 seconds of the input video (the part with the speed of 20x), and the setpts filter to adjust the presentation timestamp of the input video. By setting the presentation timestamp to PTS-START, we ensure that the output has a consistent speed throughout.
- Concatenating parts of a video in FFmpeg can be challenging when the parts have different speeds.
- Speed differences in video files can occur for a variety of reasons, including different frame rates and editing.
- To concatenate parts of a video with different speeds in FFmpeg, you can use the
setptsfilter to adjust the presentation timestamp of the input video. - By setting the presentation timestamp of each input to the same value, you can ensure that the output has a consistent speed throughout.