CODEWITHSUNDEEP
videoffmpeg
protter
protter

Reputation: 131

Create drawbox with ffmpeg between specific seconds (without reencoding whole video - faster)

My plan was to put a transparent red box behind a video. This box should only be present from second 1-45. But if the videos are 3 hours long, the process takes a long time although it only has to process 45 seconds.

My first attempt takes too long:

ffmpeg -i %1 -vf drawbox=0:9*ih/10:iw:ih/10:t=fill:[email protected]:enable='between(t,1,45)' "%~dp0transpred\%~n1%~x1

Then i tried splitting the video into two parts. put the box on the first video, and then put the two back together again.

ffmpeg -ss 00:00:00.0000 -i %1 -to 00:00:45.0000 -vf drawbox=0:9*ih/10:iw:ih/10:t=fill:[email protected]:enable='between(t,1,45)' "%~dp0transpred\%~n1A%~x1"

FFMpeg -ss 00:00:45.0000 -i %1 -c:v copy -c:a copy -avoid_negative_ts make_zero "%~dp0transpred\%~n1B%~x1"

But i don't even have to try to put these two together, because they are not separated exactly at the second. I have read that this is due to "timestamps" and the different video and audio streams.

Now I'm trying an approach to create a stream with the bar, and then overlay it with the finished video. I haven't quite managed that yet, and I don't know if it's faster. Shortening the video is very fast.

EDIT (Added as a replacement for the comment later)

Thanks for your help I have almost done it with a slightly different approach. Unfortunately, the second part now always has no sound. No matter if I put A and B (B no sound) or B and A (A no sound) together.

  1. First split with mkvmerge so i have no worrys about the keyframes and get the exact time mkvmerge --split timestamps:00:00:45.100 A.MKV -o splitmkm.mkv
  2. Then add the Bar (Black because of easier testing): ffmpeg -i splitmkm-001.mkv -vf drawbox=0:9*ih/10:iw:ih/10:t=fill BAR1.MKV
  3. Merge (mkvmerge ends with error): ffmpeg -safe 0 -f concat -i list.txt -c copy output1.mkv

EDIT (Answer to kesh)

This was the error Again, audio codec config's must match across all your concat files. The drawbox changed the audio Codec from AC-3 to Vorbis.

the procedure is now:

  1. mkvtoolnix\mkvmerge --split timestamps:00:00:05.100 %1 -o A_splitmkm.mkv with mkvmerge i have an exact split at the time, and i don't have to learn about keyframes.
  2. ffmpeg -i A_splitmkm-001.mkv -vf drawbox=0:9*ih/10:iw:ih/10:t=fill:color=red A_BARmkm.MKV create the Bar
  3. ffmpeg -i A_BARmkm.MKV -i A_splitmkm-001.mkv -map 0:v -map 1 -map -1:v -c copy A_BARwithAudio.mkv redo the step with the changed audio from drawbox
  4. ffmpeg -safe 0 -f concat -i list.txt -map 0 -c copy A_output1.mkv merge

Now everything works. Thanks alot!

Upvotes: 1

Views: 1330

Answers (1)

kesh
kesh

Reputation: 5513

See if this works for you:

ffmpeg  -ss 00:00:00.0000 -to 00:00:45.0000 -i %1 \
        -vf "color=c=red:r=1:d=1[red];color=c=0x808080:r=1:d=1,format=y8,[red]alphamerge[fore]; \
            [fore][0:v]scale2ref=w=iw:h=ih/10[f][b]; \
            [b][f]overlay=0:H-h:enable='between(t,1,45)'" \
        "%~dp0transpred\%~n1A%~x1"
  • color=c=red line: form an unsized red semi-transparent box which lasts for 1 frame over 1 second
  • [fore][back]scale2ref line: size the red box to the frame
  • [b][f]overlay line: apply the red box when needed

Because the stream foreground stream (which ends with [f]) only lasts for 1 frame, ffmpeg will only compute the box once, and overlay filter will reuse that frame until all the input video frames are processed.

On drawbox. Because you need a filled box, the above is simpler implementation IMO. If you need a boundary, the issue I faced is that it is incompatible with a transparent frame. This restriction makes it unusable with the preforming approach. [edit: to make drawbox to work with transparent frames, you need to set the option replace=1]

On your alternate splicing approach, if you cut your video at a keyframe, you should be able to make it to work. To find the keyframes, you need to use ffprobe. If you want to pursue this one, see my recent answer to another question.

Upvotes: 1

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