使用ffmpeg和xfade过滤器合并多个视频文件

Question

我需要将多个视频文件(包括音频(合并到一个视频中。我注意到xfade最近发布并使用了它，但我遇到了音频同步问题。

所有视频都具有相同的视频和音频格式/分辨率/知名度和比特率等。

以下是我用来合并5个不同持续时间的视频，具有0.5个交叉渐变：

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

上面的代码生成一个带音频的视频。第一段和第二段与音频对准，但从第二过渡开始，声音未对准。

Answer 1

您的偏移量不正确。尝试：

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

如何获取xfadeoffset值：

<1>><1>>1010<1>>21<1>

输入		+		上一个xfadeoffset	-	>	xfadeduration	offset
v0.mp4			+	0	3
v1.mp4	8	+	3	1
v2.mp4	12	+	-	21
v3.mp4	5	+	25

自动化过程将有助于处理计算偏移时的错误。我创建了一个Python脚本，用于计算并为任何大小的输入视频列表构建图形：

https://gist.github.com/royshil/369e175960718b5a03e40f279b131788

它将检查视频文件的长度(使用ffprobe(，以计算出正确的偏移量。

问题的关键是建立滤波器图并计算偏移：

# 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

它可以生成一个过滤图，如

[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]

上面的Python脚本确实帮了我很多忙，但它在偏移量计算方面有一个错误。视频流应为"video_length-fade_duration*(i+1("。

如下代码：

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

我写了一个类似但更简单的脚本：

#!/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"

---

由此产生的ffmpeg命令类似于：

ffmpeg -y -hide_banner  -i f1.mp4  -i f2.mp4 -i f3.mp4  -i f4.mp4         
-filter_complex "[0:v]copy[vfade0];[vfade0][1:v]xfade=transition=pixelize:duration=0.5:offset=-.5[vfade1];
[vfade1][2:v]xfade=transition=pixelize:duration=0.5:offset=10.0[vfade2];
[vfade2][3:v]xfade=transition=pixelize:duration=0.5:offset=20.0[vfade3];
[vfade3]format=yuv420p;
[0:a]acopy[afade0];[afade0][1:a]acrossfade=d=0.5[afade1];
[afade1][2:a]acrossfade=d=0.5[afade2];
[afade2][3:a]acrossfade=d=0.5[afade3];
[afade3]acopy"       -c:v h264_nvenc -preset p7 -profile:v high -rc-lookahead 8 -spatial_aq 1 -pix_fmt yuv420p -c:a libopus "output.mp4"

这个答案中的脚本有一个错误，这个答案指出了这个错误，但显示为一个新的def.

如果有人只想要上一个答案的更正原始脚本，请将# Prepare the filter graph之后的块替换为：

# 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)