x264 encodes - add 1 second of black to start?

[TenementLady]

Does anybody know if it is possible to script the addition of 1 second of black to the start of a video file whilst encoding via x264/ffmpeg?

It would also be useful if there was a way of scripting chapter markers to the correct the right I-frame.

[davexnet]

Yes, create a simple AVIsynth script and encode in ffmpeg/Virtualdub2, etc. For example

vid=lwlibavVideosource("S:\misc film\shorts\test.mp4")
aud=lwlibavAudiosource("S:\misc film\shorts\test.mp4")
audiodub(vid,aud)
bc=blankclip(last,length=24)
bc+last

[jagabo]

If the first frame of your video is black you can use ffmpeg's loop filter to repeat that first frame N (one second) times, and the adelay filter to delay the audio by the same amount of time (inserts silent audio). Assuming a 24 fps video:

ffmpeg -i input.mp4 -vf loop=loop=24:size=1:start=0 -af adelay=1000:all=1 -c:v libx264 -c:a aac output.mp4

The first frame is repeated 24 times (1 second); 1000 milliseconds of silent audio is inserted.

https://ffmpeg.org/ffmpeg-filters.html#loop
https://ffmpeg.org/ffmpeg-filters.html#adelay

[jagabo]

By the way, here's a mod of davexnet's AviSynth script which automatically generates the correct number of blank frames based on the video's frame rate (rather than manually specifying the number of frames):

vid=lwlibavVideosource("S:\misc film\shorts\test.mp4")
aud=lwlibavAudiosource("S:\misc film\shorts\test.mp4")
audiodub(vid,aud)
BlankClip(last, length=round(framerate))+last

If you wanted a different length of time, say 1.5 seconds, just multiply the framerate by that amount:

BlankClip(last, length=round(framerate*1.5))+last

[TenementLady]

Thanks for the suggestions, will give them a try out.