I normally just do the math. Bear in mind that 30 fps is really 30000/1001. You lose one frame of that 30 every 30-ish seconds. And it's not the only framerate in town. I normally do the math against the audio sample rate though.
* 48000 (samples per second audio)
= 2016000 total audio samples
= 1601.6 audio samples per frame
2016000 / 1601.6
so 42 seconds of video is 1258 frames plus .7413 * 48000 samples of audio. Although I tend to make my videos even seconds (with that extra audio chunk) so it looks pretty (and predictable) on youtube. Video editors like KDENlive, lives, cinelerra, ... probably show the frame count (sort of) in the seconds.frame format. Where the .### is the frame count on that second, not the fraction of seconds. Not that I would know as I do most of my editing on the CLI. But I tend to fiddle with the individual frames as images before making a video of them.
Where 42*30 would be 1260, and 2 additional frames that might not otherwise exist, or get truncated if you use -shortest when muxing the audio and video together.
Last edited by Shadow_7; 03-16-2015 at 07:46 AM.