On 10 October 2014 06:54, Luca Barbato wrote: > On 05/10/14 12:57, Leon Brooks wrote: > >> In overlaying graphics/text onto a video stream, there is *no option* with >> which to defer the start of the overlay clip. >> >> There is also (AFAICT) *no video-file format* which includes transparency, >> so the clip has to be provided as a humungous collection of PNG images >> (short example here: https://www.youtube.com/watch?v=7aXnmuoiO4Q), it >> cannot be turned into a video then the '-itsoffset' option used to bump it >> along. >> > > There are few formats supporting transparency, the problem starts with > creating them I guess. >
Examples would be good. :-) > So why not use the 'fade' filter? >> >> Every experiment thus far has had it ditching the alpha (transparency) >> information, thus overlaying the main video stream with a black >> background, >> then the actual overlay. >> > This would be good to deal with, regardless of the other details. The movie filter has a 'seek_point' option which skips a certain portion of >> the overlay when starting to write it atop the base video. One (I hope) of >> two possible options would make this more useful. Each option would take a >> single argument, being the start time within the base video at which the >> overlaying begins. >> >> This could be done either by simply not overlaying until that point, or by >> repeatedly overlaying just the first frame of the overlay video (so in my >> case, prepending a transparent PNG to the sequence would achieve that). >> >> In the first case, an option entitled 'overlay_from' would sound about >> right. >> >> The second case is not so easy to name. Using 'repeat_until' describes >> exactly what it does, however does not mention what it is repeating. >> Morphing that into 'repeat_1st_until' overcomes that shortfall, yet sounds >> less elegant. >> >> Adding another option 'repeat_to_end' would simplify watermarking-type >> operations, by watermarking up to the overlay start with the first frame, >> then watermarking a section with the intervening frames of the overlay >> movie, then watermarking from there to the end of the base video with the >> final frame. >> > > You have plenty of interesting ideas and insights. The ideas and insights are (for me, anyway) easy and natural. Making things happen with regard to those ideas is the more difficult part. Probably I won't be able to try something on this area for the next months, > but if you want to try yourself please join us on freenode #libav-devel =) > A good suggestion. At a less hectic time (maybe Sunday or Monday?), AusTux will join the channel. -- *Cheers — Leon*
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