Would someone please check my findings
Latest git version
I had assumed that the “higher quality” index frames from a BlackVue mp4 (1fps) were always present in the mapillary_tools image output. This does not appear to be the case. Using the fps filter (standard tools processing) and comparing against the first and last index frames in the stream (at 2fps) I found no commom images.
I then ran it in standard rate mode, eg;
ffmpeg -i video.mp4 -r 2 -vsync vfr -qscale:v 1 RFile_%3d.jpg
and every 2nd frame matched an index.
To generate index only frames for testing;
ffmpeg -i video.mp4 -vf “select=eq(pict_type,I)” -vsync vfr -qscale:v 1 IFile_%3d.jpg
The standard tools command
ffmpeg -i video.mp4 -vf fps=1/0.5 -qscale:v 1 MFile_%3d.jpg
I realize this is deprecated, but it may be worth looking into the server side processing of uploaded videos. The small increase in quality may be worth it.
Also note that -qscale:v 1 will in fact default to -qscale:v 2 unless the -qmin 1 switch is added. I think this roughly equates to a jpg quality of 84% vs 95% or higher