Add "-probesize" and "-analyzeduration" flags to ffmpeg to fix some files not playing

[Giovanni Musto]

Some files that need transcoding won't play since ffmpeg can't find some parameters for the input, for example the pixel format, as also described here: https://superuser.com/questions/1181422/unable-to-parse-option-value-1-as-pixel-format-when-transcoding-mp4-to-mp4-us Adding -probesize and -analyzeduration flags, even just with a few MBs (maybe 50?) should solve the problem.