ffmpeg video-editing batch-processing concat python

Batch merging videos with ffmpeg without rendering

Editing notes

By Pixel Li · April 14, 2022

中文原文 →

Merging 2 videos (requires rendering)

Reference: FFmpeg split video and merge back

Suppose 1.mp4 needs all its segments, 2.mp4 needs the segment after 3 seconds, and both audio tracks are kept. Then the following code works. But this method requires re-rendering.

  • [0:v] refers to the video of the 1st input
  • [0:a] refers to the audio of the 1st input
  • [v0] refers to saving this line as [v0]
  • [v0][a0][v1][a1] indicates the export order
  • concat=n=2 means the merged video has 2 segments
  • :v=1:a=1 means both audio and video are exported
  • -map "[outv]" means redefining the timestamps of [outv]
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$ ffmpeg -i 1.mp4 -i 2.mp4 -filter_complex "\
[0:v]trim=start=0,setpts=PTS-STARTPTS[v0]; \
[0:a]atrim=start=0,asetpts=PTS-STARTPTS[a0]; \
[1:v]trim=start=3,setpts=PTS-STARTPTS[v1]; \
[1:a]atrim=start=3,asetpts=PTS-STARTPTS[a1]; \
[v0][a0][v1][a1]concat=n=2:v=1:a=1[outv][outa]" \
-map "[outv]" -map "[outa]" output.mp4

Removing the first 3 seconds

Reference: Cut part from video file from start position to end position with FFmpeg

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$ ffmpeg -ss [start] -i in.mp4 -t [duration] -c copy out.mp4

If you only need to remove the first 3 seconds of 1.mp4 and save the rest to output.mp4, you can omit -t [duration]:

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$ ffmpeg -ss 3 -i 1.mp4 -c copy output.mp4

Merging 2 videos (no rendering needed)

Reference: How to Merge two videos without re-encoding

You must make sure the two videos have the same basic settings — codec, dimensions, fps and so on — or they won’t merge correctly!

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ffmpeg -f concat -fase 0 -i list.txt -c copy output.mp4

list.txt needs to be in the current folder, with the following content format:

file '1.mp4'
file '2.mp4'

Batch-processing the files that need merging in the current folder with Python

Suppose every 2 files need to be merged, with files named 1.mp4 and 1-intro.mp4. Then you first need to create 1 txt file for each batch:

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# -*- coding: utf-8 -*-
import os

files = [f for f in os.listdir('.') if os.path.isfile(f)]
for f in files:
    if (f.endswith(".mp4"):
        with open("%s.txt" % f, "w") as file:
            intro = f.rsplit('.', 1)[0]
            file.write("file '%s-intro.mp4'\nfile '%s'" % (intro,f))

The result is a 1.mp4.txt file with the content:

file '1-intro.mp4'
file '1.mp4'

Now we can merge 1-intro.mp4 and 1.mp4 into 1 file via 1.mp4.txt:

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# -*- coding: utf-8 -*-
import os
import subprocess

files = [f for f in os.listdir('.') if os.path.isfile(f)]

for f in files:
    if (f.endswith(".mp4") and "intro" not in f):
        filename = f.rsplit('.', 1)[0]
        cmd = "ffmpeg -f concat -safe 0 -i '%s.txt' -c copy '%s-final.mp4'" % (f, filename)
        print(cmd)
        p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE, stderr=subprocess.PIPE)
        p.wait()
    else:
        continue

The generated file is 1-final.mp4, along with other file groups named in the same format.

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