Extract X Frames From Specific Times to JPG Files

The following will take a given input video (e.g. bunny.mp4) and by using the select filter, will only let frames at a specific time (or any valid Expression) pass through.

Since ffmpeg is designed to process an input media file(s) in a frame-by-frame basis. By default, the output of a filter chain will be the same frame rate as the input. This is defined as ‘presentation timestamp’ or PTS in short.

To override this, we need to modify the PTS of the output using the setpts filter.

Without it, when the select condition is met, the frame will pass through. However, when the condition is false and in the lack of any frame data to fill into the needed output frame rate, ffmpeg will repeat the last known frame.

To fix that, we want to limit the PTS to the number of unique frames generated by the select filter. The expression N / FRAME_RATE / TB will do exactly that.

To generate jpg output files, I follow the same principles of the ‘Conver Video File to jpeg Images’ example.