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.
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.
ffprobe
.Automating the process will help deal with errors in calculating the offsets. I created a Python script that makes the calculation and builds a graph for any size list of input videos:
https://gist.github.com/royshil/369e175960718b5a03e40f279b131788
It will check the lengths of the video files (with ffprobe
) to figure out the right offsets.
The crux of the matter is to build the filter graph and calculating the offsets:
# Prepare the filter graph
video_fades = ""
audio_fades = ""
last_fade_output = "0:v"
last_audio_output = "0:a"
video_length = 0
for i in range(len(segments) - 1):
# Video graph: chain the xfade operator together
video_length += file_lengths[i]
next_fade_output = "v%d%d" % (i, i + 1)
video_fades += "[%s][%d:v]xfade=duration=0.5:offset=%.3f[%s]; " % \
(last_fade_output, i + 1, video_length - 1, next_fade_output)
last_fade_output = next_fade_output
# Audio graph:
next_audio_output = "a%d%d" % (i, i + 1)
audio_fades += "[%s][%d:a]acrossfade=d=1[%s]%s " % \
(last_audio_output, i + 1, next_audio_output, ";" if (i+1) < len(segments)-1 else "")
last_audio_output = next_audio_output
It may produce a filter graph such as
[0:v][1:v]xfade=duration=0.5:offset=42.511[v01];
[v01][2:v]xfade=duration=0.5:offset=908.517[v12];
[v12][3:v]xfade=duration=0.5:offset=1098.523[v23];
[v23][4:v]xfade=duration=0.5:offset=1234.523[v34];
[v34][5:v]xfade=duration=0.5:offset=2375.523[v45];
[v45][6:v]xfade=duration=0.5:offset=2472.526[v56];
[v56][7:v]xfade=duration=0.5:offset=2659.693[v67];
[0:a][1:a]acrossfade=d=1[a01];
[a01][2:a]acrossfade=d=1[a12];
[a12][3:a]acrossfade=d=1[a23];
[a23][4:a]acrossfade=d=1[a34];
[a34][5:a]acrossfade=d=1[a45];
[a45][6:a]acrossfade=d=1[a56];
[a56][7:a]acrossfade=d=1[a67]
The Python script above did help me a lot but it has a mistake in offset calculation. The video stream should be 'video_length - fade_duration*(i+1)'.
As the code below:
def gen_filter(segments):
video_fades = ""
audio_fades = ""
settb = ""
last_fade_output = "0:v"
last_audio_output = "0:a"
fade_duration = 0.3
video_length = 0
file_lengths = [0]*len(segments)
for i in range(len(segments)):
settb += "[%d]settb=AVTB[%d:v];" % (i,i)
for i in range(len(segments)-1):
file_lengths[i] = float(ffmpeg.probe(segments[i])['format']['duration'])
video_length += file_lengths[i]
next_fade_output = "v%d%d" % (i, i + 1)
video_fades += "[%s][%d:v]xfade=transition=fade:duration=%f:offset=%f%s%s" % \
(last_fade_output, i + 1, fade_duration, video_length - fade_duration*(i+1), '['+next_fade_output+'];' if (i) < len(segments)-2 else "","" if (i) < len(segments)-2 else ",format=yuv420p[video];")
last_fade_output = next_fade_output
next_audio_output = "a%d%d" % (i, i + 1)
audio_fades += "[%s][%d:a]acrossfade=d=%f%s" % \
(last_audio_output, i + 1, fade_duration*2, '['+next_audio_output+'];' if (i) < len(segments)-2 else "[audio]")
last_audio_output = next_audio_output
return settb + video_fades + audio_fades
The script in this answer has a mistake, which was pointed out by this answer but presented as a new def.
If anyone just wants the corrected original script for the previous answer, replace the chunk after # Prepare the filter graph
with:
# Prepare the filter graph
video_fades = ""
audio_fades = ""
last_fade_output = "0:v"
last_audio_output = "0:a"
video_length = 0
fade_duration = 0.5
for i in range(len(segments) - 1):
# Video graph: chain the xfade operator together
video_length += file_lengths[i]
next_fade_output = "v%d%d" % (i, i + 1)
video_fades += "[%s][%d:v]xfade=duration=0.5:offset=%.3f[%s]; " % \
(last_fade_output, i + 1, video_length - fade_duration*(i+1), next_fade_output)
last_fade_output = next_fade_output
# Audio graph:
next_audio_output = "a%d%d" % (i, i + 1)
audio_fades += "[%s][%d:a]acrossfade=d=1[%s]%s " % \
(last_audio_output, i + 1, next_audio_output, ";" if (i+1) < len(segments)-1 else "")
last_audio_output = next_audio_output
# Assemble the FFMPEG command arguments
ffmpeg_args = ['ffmpeg',
*itertools.chain(*files_input),
'-filter_complex', video_fades + audio_fades,
'-map', '[%s]' % last_fade_output,
'-map', '[%s]' % last_audio_output,
'-y',
args.output_filename]
# Run FFMPEG
subprocess.run(ffmpeg_args)
I wrote a similar but simpler script :
#!/bin/bash
# usage: ls -1 something*.mp4 | ffmpeg_xfade.sh output.mp4
fdur=0.5
ftrans=pixelize
f0n=0
f1n=1
alld=0
while read f; do
allvf="$allvf$vf"
allaf="$allaf$af"
inputs="$inputs -i $f "
d=$(ffprobe -v error -select_streams v:0 -show_entries stream=duration -of default=noprint_wrappers=1:nokey=1 "$f")
alld=$(bc -l <<< "$alld + $d")
offset=$(bc -l <<< "$alld - $fdur * $f1n")
vf="[vfade$f0n][$f1n:v]xfade=transition=$ftrans:duration=$fdur:offset=$offset[vfade$f1n];"
af="[afade$f0n][$f1n:a]acrossfade=d=$fdur[afade$f1n];"
(( f0n++ ))
(( f1n++ ))
done
f0n=$(( f0n - 1 ))
allvf="[0:v]copy[vfade0];$allvf[vfade$f0n]format=yuv420p"
allaf="[0:a]acopy[afade0];$allaf[afade$f0n]acopy"
#set -vx
ffmpeg -y -hide_banner $inputs \
-filter_complex "$allvf;$allaf" \
-c:v h264_nvenc -preset p7 -profile:v high -rc-lookahead 8 -spatial_aq 1 -pix_fmt yuv420p \
-c:a libopus \
"$1"
我写了类似但恕我直言更简单的脚本https://github.com/yekm/etc/blob/home/bin/ffmpeg_xfade.sh
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