如何无需重新编码合并两个视频？现有耗时方案需优化

Hey there! Let’s sort out that slow, resource-hogging video merge problem you’re dealing with. The core issue with your current approach is that you’re unnecessarily re-encoding both videos to create intermediate files (the -qscale 0 flag triggers a lossless re-encode, which is why it’s eating up CPU time and system resources).

Here’s how to merge your videos without any re-encoding—this method is way faster, uses minimal resources, and skips those wasteful intermediate files:

Best Methods for Lossless (No Re-Encode) Merging #

1. For Videos with Identical Codecs & Containers (Most Common Scenario) #

Use FFmpeg’s Concat Demuxer (Recommended)

This is the most reliable way to merge videos without re-encoding. Here’s how to set it up:

1. First, create a text file (let’s call it video_list.txt) that lists your input videos:

   file '/full/path/to/your/first/video.mp4'
   file '/full/path/to/your/second/video.mp4'
   

2. Run this single FFmpeg command to merge them directly:

   cpulimit -l 90 ffmpeg -f concat -safe 0 -i video_list.txt -c copy /var/www/html/myserver/merg/$(uniqid)_merge.$ext
   

   • -c copy: Tells FFmpeg to directly copy the video/audio streams instead of re-encoding them (this is the key for speed).
   • -f concat: Specifies we’re using FFmpeg’s concat demuxer for merging.
   • -safe 0: Allows using absolute file paths in the text list (skip this if you use relative paths).

Alternative: Concat Protocol (For Simple Cases)

If you’re working with container formats that support direct concatenation (like MPEG-TS), you can skip the text file and use this one-liner:

cpulimit -l 90 ffmpeg -i "concat:$filename1|$filename2" -c copy /var/www/html/myserver/merg/$(uniqid)_merge.$ext

Note: This doesn’t work well with MP4 files (due to MP4’s internal structure), so stick to the demuxer method for MP4s.

2. For Videos with Matching Codecs but Different Containers #

If your videos use the same video/audio codecs but different containers (e.g., one MP4, one MKV), you can still merge without re-encoding using the concat demuxer. Just target your desired output container (e.g., MP4) and add a flag for better streaming compatibility:

cpulimit -l 90 ffmpeg -f concat -safe 0 -i video_list.txt -c copy -movflags +faststart /var/www/html/myserver/merg/$(uniqid)_merge.mp4

The -movflags +faststart option rearranges the MP4 file’s metadata to make it stream-friendly (great if you’re hosting the merged video online).

Why Your Original Approach Was Inefficient #

Your current code runs two separate FFmpeg commands with -qscale 0, which forces a lossless re-encode of each video. Even though it’s lossless, this process requires decoding the original video, re-compressing it, and writing new intermediate files—wasting CPU, time, and disk space. The methods above skip all that by copying the original streams directly.

内容的提问来源于stack exchange，提问作者Yogesh Agarwal