I have the following command working in ffmpeg, which adds 1 second of a black frame to the beginning of the video. However, I lose the audio from the original video in the output video. How can I adjust the command to make sure the original audio stays with the final output, or better yet, there is 1 second of "blank" audio at the beginning so it matches the new output video.
ffmpeg -i originalvideo -f lavfi -i color=c=black:s=1920x1080:r=25:sar=1/1 -filter_complex "[0:v] setpts=PTS-STARTPTS [main]; [1:v] trim=end=1,setpts=PTS-STARTPTS [pre]; [pre][main] concat=n=2:v=1:a=0 [out]" -map "[out]" finaloutputvideo.mp4
You need to generate or add audio to be associated with the black video because each concatenated section needs the same number of video and audio streams.
ffmpeg \
-i originalvideo \
-f lavfi -i color=c=black:s=1920x1080:r=25:sar=1/1:d=1 \
-t 1 -f lavfi -i anullsrc=channel_layout=stereo:sample_rate=44100 \
-filter_complex \
"[0:v]setpts=PTS-STARTPTS[mainv]; \
[0:a]asetpts=PTS-STARTPTS[maina]; \
[1:v][2:a][mainv][maina]concat=n=2:v=1:a=1[v][a]" \
-map "[v]" -map "[a]" -movflags +faststart output.mp4
You can eliminate the (a)setpts filters for the color and anullsrc source filters since their timestamps start at 0.
You can avoid the trim filter because you can set the duration for each filter.
The -t value for the anullsrc duration only needs to be less than or equal to the duration of the black video: the concat filter will automatically pad the rest with silence.
With anullsrc ensure that you match the proper channel layout and audio sample rate of your main video; otherwise concat may automatically choose a "common" layout and rate that may not be what you want.