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videoffmpegconcatenationcross-fade

Merging multiple video files with ffmpeg and xfade filter

I need to merge multiple video files (with included audio) into a single video. I've noticed xfade has been recently released and used it but I am running into an audio sync issue.

All videos are in the same format / resolution / fame and bitrate / etc both for video and audio.

Here is what I am using to merge 5 videos of various durations with 0.5 crossfade transitions:

ffmpeg \
-i v0.mp4 \
-i v1.mp4 \
-i v2.mp4 \
-i v3.mp4 \
-i v4.mp4 \
-filter_complex \
"[0][1]xfade=transition=fade:duration=0.5:offset=3.5[V01]; \
 [V01][2]xfade=transition=fade:duration=0.5:offset=32.75[V02]; \
 [V02][3]xfade=transition=fade:duration=0.5:offset=67.75[V03]; \
 [V03][4]xfade=transition=fade:duration=0.5:offset=98.75[video]; \
 [0:a][1:a]acrossfade=d=0.5:c1=tri:c2=tri[A01]; \
 [A01][2:a]acrossfade=d=0.5:c1=tri:c2=tri[A02]; \
 [A02][3:a]acrossfade=d=0.5:c1=tri:c2=tri[A03]; \
 [A03][4:a]acrossfade=d=0.5:c1=tri:c2=tri[audio]" \
-vsync 0 -map "[video]" -map "[audio]" out.mp4

The code above generates a video with audio. The first and second segment is aligned with audio but starting with the second transition the sound is misaligned.

Solution

  • Your offsets are incorrect. Try:

    ffmpeg -i v0.mp4 -i v1.mp4 -i v2.mp4 -i v3.mp4 -i v4.mp4 -filter_complex \
"[0][1:v]xfade=transition=fade:duration=1:offset=3[vfade1]; \
 [vfade1][2:v]xfade=transition=fade:duration=1:offset=10[vfade2]; \
 [vfade2][3:v]xfade=transition=fade:duration=1:offset=21[vfade3]; \
 [vfade3][4:v]xfade=transition=fade:duration=1:offset=25,format=yuv420p; \
 [0:a][1:a]acrossfade=d=1[afade1]; \
 [afade1][2:a]acrossfade=d=1[afade2]; \
 [afade2][3:a]acrossfade=d=1[afade3]; \
 [afade3][4:a]acrossfade=d=1" \
-movflags +faststart out.mp4

    How to get xfade offset values:

    input input duration + previous xfade offset - xfade duration offset =
    v0.mp4 4 + 0 - 1 3
    v1.mp4 8 + 3 - 1 10
    v2.mp4 12 + 10 - 1 21
    v3.mp4 5 + 21 - 1 25

    These are simplified example durations that are different than the durations shown in the original question.