> -----Original Message----- > From: ffmpeg-user [mailto:[email protected]] On Behalf Of > Moritz Barsnick > Sent: 06 October 2016 18:34 > To: FFmpeg user discussions > Subject: Re: [FFmpeg-user] Selecting/dropping frames without re-encoding > > On Thu, Oct 06, 2016 at 16:07:02 +0200, Moritz Barsnick wrote: > > I found the suggestion to use the concat demuxer with streamcopy very > > interesting. Assuming it can seek and cut precisely, that could work - > > again in theory. Let's experiment with that. :) > > So, where are your results, everyone? ;-) Here are mine. > > I created a 50 fps DNxHR MXF file. The testsrc2 filter/source kindly puts the > frame numbers onto each frame: > > $ ffmpeg -f lavfi -i testsrc2=s=hd720:r=50 -c:v dnxhd -profile:v dnxhr_hq -t 3 > input.mxf > > I created a concat script for these three seconds, to select every second > frame, which means stepping forward by 0.040 (two frames at 50 fps), for a > duration of 0.020 (one frame): > > $ perl -e 'print "ffconcat version 1.0\n\n"; my $t = 0; while ($t <= 3) { > printf("file input.mxf\ninpoint %1.3f\nduration 0.020\noutpoint %1.3f\n\n", > $t, $t + 0.020); $t += 0.040; }' > concatscript.txt > > Then I used this concat demuxer script to do the actual extraction: > > $ ffmpeg -r 25 -f concat -i concatscript.txt -c:v copy output.mxf > > Visual inspection of the result shows me that every second frame was > extracted, at a resulting frame rate of 25 fps. > > Verifying with the frashhash demuxer showed me that every second frame > is indeed identical: > > $ ffmpeg -i input.mxf -c copy -f framehash input.mxf.hash $ ffmpeg -i > output.mxf -c copy -f framehash output.mxf.hash > > Bingo! :-)
Well done :-) > > Still, a bitstream filter would be nifty. ;-) > > Moritz > _______________________________________________ > ffmpeg-user mailing list > [email protected] > http://ffmpeg.org/mailman/listinfo/ffmpeg-user > > To unsubscribe, visit link above, or email [email protected] > with subject "unsubscribe". _______________________________________________ ffmpeg-user mailing list [email protected] http://ffmpeg.org/mailman/listinfo/ffmpeg-user To unsubscribe, visit link above, or email [email protected] with subject "unsubscribe".
