[FFmpeg-user] Some Questions on Time Delta between Frame Display and Frame Capture. Thoughts?

Hassan hassaniqbal931 at gmail.com
Mon Mar 22 17:55:58 EET 2021


I have few questions about FPS while recording a video.

Suppose, I am capturing a video by recording my desktop. The video is
playing at 60 FPS. My frame rate for capturing is also set at 60 FPS.
Ideally, at 60 FPS, each of the subsequent frames is 16.6 msec apart. For
this scenario, I have the following questions:
1. Does FFmpeg record desktop at the refresh rate of the LCD, like whenever
a new frame is displayed, does it captures it right away or it records at
its own set fixed rate?
2. What is the likely delta between the time (t1) when a frame of the video
appears on LCD and the time (t2) when the FFmpeg captures? For example,
since the inter-frame interval is 16.6 msec, in the worse case, is it
possible that t2-t1 is approximately 16 msec?
3. If the answer to question (2) is yes, then how do we address this issue
to reduce this delta?

One top-of-the-head solution to question 3 is to record a video at a higher
frame-rate, say 120 FPS. However, if this works, it will reduce the error
by 50%.
What are better approaches to address this problem?


Hassan Iqbal

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