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ffmpeg -i "a.mov" -i "b.mp4" -filter_complex "[0:v]setsar=sar=${SAR}[a]; [1:v]setsar=sar=${SAR}[b]; [a][0:a] [b][1:a] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" -preset veryfast -crf 18 "merged.mp4"

using the above code I am able to successfully merge a.mov(1920x816) with b.mov(1920x816). However, Youtube end screens require video to be 16:9 aspect ratio. Thus I tried scale filter and setting SAR to 16:9. however this leads to the output video stretching to fit the 16:9 ratio.

How can I output a video with 16:9 ratio with the actual video with resolution 1920x816. Essentially The remaining vertical space should just be black without stretching the 816 height video to fit the 1080 height.

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Have you tried uploading it to Youtube? Their player window will be a fixed 16:9 ratio (on YT.com), but they should accept source videos of any ratio, and simply center it in their window during playback.

Anyway, here's the method:
ffmpeg -i "a.mov" -i "b.mp4" -filter_complex "[0:v]scale=iw*sar:ih,pad=if(gt(dar,16/9),iw,2*trunc(ih*16/9/2)):if(gt(dar,16/9),2*trunc(iw*9/16/2),ih):(ow-iw)/2:(oh-ih)/2,setsar=1[a]; [1:v]scale=iw*sar:ih,pad=if(gt(dar,16/9),iw,2*trunc(ih*16/9/2)):if(gt(dar,16/9),2*trunc(iw*9/16/2),ih):(ow-iw)/2:(oh-ih)/2,setsar=1[b]; [a][0:a] [b][1:a] concat=n=2:v=1:a=1 [v] [a]" -map "[v]" -map "[a]" -preset veryfast -crf 18 "merged.mp4

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  • Same question as the other comment, what if the aspect ratio is, for example 13 : 6. Will it work if I change the command to - "-filter_complex", "[0:v]pad=iw:if(lte(ih\\,iw)\\,ih\\,2*trunc(iw*13/6/2)):(ow-iw)/2:(oh-ih)/2[v0];[1:v][v0]scale2ref[v1][v0];[v0][v1]overlay=x=(W-w)/2:y=(H-h)/2[v]" ?
    – HB.
    Jul 9, 2019 at 10:04
  • Assuming 13/6 is the required output DAR, replace 16/9 in my command with 13/6 and 9/16 with 6/13.
    – Gyan
    Jul 9, 2019 at 11:45
  • This is the filter I used for a video that has 16/9 aspect ratio [0:v]pad=iw:if(lte(ih\\,iw)\\,ih\\,2trunc(iw*16/9/2)):(ow-iw)/2:(oh-ih)/2[v0];[1:v][v0]scale2ref[v1][v0];[v0][v1]overlay=x=(W-w)/2:y=(H-h)/2[v] Am I correct in changing the filter to the following if the aspect ratio is 13/6 [0:v]pad=iw:if(lte(ih\\,iw)\\,ih\\,2*trunc(iw*13/6/2)):(ow-iw)/2:(oh-ih)/2[v0];[1:v][v0]scale2ref[v1][v0];[v0][v1]overlay=x=(W-w)/2:y=(H-h)/2[v].
    – HB.
    Jul 9, 2019 at 12:18
  • The first filter mentioned above works perfectly for video's that has an aspect ratio of 16/9 (without using DAR), that is why I was wondering if I could just change the trunc value to iw*13/6/2 instead of iw*16/9/2?
    – HB.
    Jul 9, 2019 at 12:18
  • I asked a new question, can you please have a look? video.stackexchange.com/questions/28036/…
    – HB.
    Jul 10, 2019 at 10:41

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