[FFmpeg-user] SMPTE when converting to JPEGs

[Wolfgang Hugemann]

I converted a video taken by a supervision (security) camera into a 
sequence of JPEGs with embedded SMPTE. (My aim is to calculate the 
vehicle speed for an accident recorded in the background.)

The original AVI-container (AVC coded) claims to have a frame rate of 30 
fps, which to my experience is not a reliable information. When I 
convert it into a sequence of JPEGs or another video, I realise that 
roughly every 5th frame is doubled, with the SMPTE repeated in both 
frames. (The frame counter in the SMPTE runs from 0 to 29, with every 
about fith number doubled.)

So I guess that the SMPTE is that of the original video (?). Is it 
embedded in the original video and read from there? I can't rather be 
kind of a frame count. BTW: If I display the frame number, the 
equivalent thing happens: n is repeated every about five frames.

How does thi swork internally?

Wolfgang Hugemann