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diff --git a/doc/filters.texi b/doc/filters.texi index 363a7f5..18f46f9 100644 --- a/doc/filters.texi +++ b/doc/filters.texi @@ -1163,6 +1163,122 @@ scale="trunc(3/2*iw/hsub)*hsub:trunc(3/2*ih/vsub)*vsub" scale='min(500\, iw*3/2):-1' @end example +@section select +Select frames to pass in output. + +It accepts in input an expression, which is evaluated for each input +frame. If the expression is evaluated to a non-zero value, the frame +is selected and passed to the output, otherwise it is discarded. + +The expression can contain the following constants: + +@table @option +@item PI +Greek PI + +@item PHI +golden ratio + +@item E +Euler number + +@item n +the sequential number of the filtered frame, starting from 0 + +@item selected_n +the sequential number of the selected frame, starting from 0 + +@item prev_selected_n +the sequential number of the last selected frame, NAN if undefined + +@item TB +timebase of the input timestamps + +@item pts +the PTS (Presentation TimeStamp) of the filtered video frame, +expressed in @var{TB} units, NAN if undefined + +@item t +the PTS (Presentation TimeStamp) of the filtered video frame, +expressed in seconds, NAN if undefined + +@item prev_pts +the PTS of the previously filtered video frame, NAN if undefined + +@item prev_selected_pts +the PTS of the last previously filtered video frame, NAN if undefined + +@item prev_selected_t +the PTS of the last previously selected video frame, NAN if undefined + +@item start_pts +the PTS of the first video frame in the video, NAN if undefined + +@item start_t +the time of the first video frame in the video, NAN if undefined + +@item pict_type +the picture type of the filtered frame, can assume one of the following +values: +@table @option +@item PICT_TYPE_I +@item PICT_TYPE_P +@item PICT_TYPE_B +@item PICT_TYPE_S +@item PICT_TYPE_SI +@item PICT_TYPE_SP +@item PICT_TYPE_BI +@end table + +@item interlace_type +the frame interlace type, can assume one of the following values: +@table @option +@item INTERLACE_TYPE_P +the frame is progressive (not interlaced) +@item INTERLACE_TYPE_T +the frame is top-field-first +@item INTERLACE_TYPE_B +the frame is bottom-field-first +@end table + +@item key +1 if the filtered frame is a key-frame, 0 otherwise + +@item pos +the position in the file of the filtered frame, -1 if the information +is not available (e.g. for synthetic video) +@end table + +The default value of the select expression is "1". + +Some examples follow: + +@example +# select all frames in input +select + +# the above is the same as: +select=1 + +# skip all frames: +select=0 + +# select only I-frames +select='eq(pict_type\,PICT_TYPE_I)' + +# select one frame every 100 +select='not(mod(n\,100))' + +# select only frames contained in the 10-20 time interval +select='gte(t\,10)*lte(t\,20)' + +# select only I frames contained in the 10-20 time interval +select='gte(t\,10)*lte(t\,20)*eq(pict_type\,PICT_TYPE_I)' + +# select frames with a minimum distance of 10 seconds +select='isnan(prev_selected_t)+gte(t-prev_selected_t\,10)' +@end example + @anchor{setdar} @section setdar |