video - FFmpeg concatenation, no Audio in Final Output

Question

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

Answer 1

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.