通过 ffmpeg 无损剪切/拼接视频

傷城~ 2021-06-26 16:06 650阅读 0赞

剪切/拼接视频文件是一种常见需求。在线视频网站现在往往将一个视频文件分割成 `n` 段，以减少流量消耗。使用 `DownloadHelper/DownThemAll` 这类工具下载下来的往往就是分割后的文件。能实现剪切/拼接视频文件的工具多种多样，但往往都需要进行视频重编码（`transcoding`），这就不可避免的带来了视频质量上的损耗，更不用提那长的令人发指的转换时间了…

其实借助 `ffmpeg` 我们就可以在不进行视频重编码的情况下完成此类任务：

剪切：

ffmpeg -i input.mp4 -ss **START_TIME** -t **STOP_TIME** -acodec copy -vcodec copy output.mp4

其中 `START_TIME/STOP_TIME` 的格式可以写成两种格式：

1.  以秒为单位计数： 80
2.  时:分:秒： 00:01:20

拼接 :

拼接的情况稍微复杂些，我们需要将需要拼接的视频文件按以下格式保存在一个列表 `list.txt` 中：

file '/path/to/file1'
    file '/path/to/file2'
    file '/path/to/file3'

相应的命令为：

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

由于不需要重编码，这两条命令几乎是即时完成的。

方便起见，我写了一个脚本来简化操作。放在 `github` 上，请自取：  
https://gist.github.com/imcaspar/8771268

#!/bin/bash
    #cut/join videos using ffmpeg without quality loss
    
    if [ "$(uname)" == "Darwin" ]; then
        if ! [ -x "$(command -v brew)" ]; then
           echo 'homebrew is not installed.'
           /usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)"
        fi
        if ! [ -x "$(command -v ffmpeg)" ]; then
           echo 'ffmpeg is not installed.'
           brew install ffmpeg
        fi
    
    elif [ "$(expr substr $(uname -s) 1 5)" == "Linux" ]; then
        if ![ -x "$(command -v ffmpeg)" ]; then
           echo 'ffmpeg is not installed.'
        fi
    fi
    
    if [ -z $1 ] || [ -z $2 ]; then
       echo "Usage:$0 c[ut] seconds <File>"
       echo " eg. $0 c 10 80 example.mp4"
       echo " eg. $0 c 00:00:10.100 00:01:20.200 example.mp4"
       echo "Usage:$0 j[oin] <FileType>"
       echo " eg. $0 j avi"
       exit
    fi
     
    case "$1" in
       c)
          echo "cuttig video..."
          echo $4
          fileName=$(echo $4 | rev | cut -f 2- -d '.' | rev)
          fileType=$(echo $4 | rev | cut -f 1 -d '.' | rev)
          echo $fileName
          echo $fileType
          startTime=$( echo "$2" | tr ':' '_')
          endTime=$( echo "$3" | tr ':' '_' )
          echo $escapedFileName
          ffmpeg -i "$4" -ss $2 -to $3 -acodec copy -vcodec copy "$fileName-$startTime-$endTime.mp4"
          ;;
       j)
          echo "joinning videos..."
          rm temp_list.txt      
          for f in `ls *.$2 | sort -k 1n -t '.'`; do echo "file '$f'" >> temp_list.txt; done
          #printf "file '%s'\n" ./*.$2 > temp_list.txt
          ffmpeg -f concat -i temp_list.txt -c copy output.$2
          rm temp_list.txt
          ;;
       *)
          echo "wrong arguments"
          ;;
    esac
    exit

以上拼接操作生效的前提是，所有视频文件的格式编码相同，如果需要拼接不同格式的视频文件可以借助以下脚本：

#!/bin/bash
    
    ################################################################################
    #
    # Script name: MultiMedia Concat Script (mmcat)
    # Author: burek (burek021@gmail.com)
    # License: GNU/GPL, see http://www.gnu.org/copyleft/gpl.html
    # Date: 2012-07-14
    #
    # This script concatenates (joins, merges) several audio/video inputs into one
    # final output (just like as if all the inputs were played in a playlist, one
    # after another).
    #
    # All input files must have at least one audio and at least one video stream.
    # If not, you can easily add audio silence, using FFmpeg. Just search the
    # internet for "ffmpeg add silence".
    #
    # The script makes use of FFmpeg tool (www.ffmpeg.org) and is free for use under
    # the GPL license. The inspiration for this script came from this FAQ item:
    # http://ffmpeg.org/faq.html#How-can-I-join-video-files_003f
    #
    # If you find any bugs, please send me an e-mail so I can fix it.
    #
    ################################################################################
    #
    # General syntax: mmcat <input1> <input2> <input3> ... <output>
    #
    # For example: mmcat file1.flv file2.flv output.flv
    # would create "output.flv" out of "file1.flv" and "file2.flv".
    #
    ################################################################################
    
    # change this to what you need !!!
    EXTRA_OPTIONS='-vcodec libx264 -crf 23 -preset medium -acodec aac -strict experimental -ac 2 -ar 44100 -ab 128k'
    
    ################################################################################
    #
    # NO NEED TO TOUCH ANYTHING AFTER THIS LINE!
    #
    ################################################################################
    
    # the version of the script
    VERSION=1.3
    
    # location of temp folder
    TMP=/tmp
    
    ################################################################################
    
    echo "MultiMedia Concat Script v$VERSION (mmcat) - A script to concatenate multiple multimedia files."
    echo "Based on FFmpeg - www.ffmpeg.org"
    echo "Don't forget to edit this script and change EXTRA_OPTIONS"
    echo ""
    
    ################################################################################
    # syntax check (has to have at least 3 params: infile1, infile2, outfile
    ################################################################################
    if [ -z $3 ]; then
    	echo "Syntax: $0 <input1> <input2> <input3> ... <output>"
    	exit 1
    fi
    
    ################################################################################
    # get all the command line parameters, except for the last one, which is output
    ################################################################################
    # $first - first parameter
    # $last - last parameter (output file)
    # $inputs - all the inputs, except the first input, because 1st input is
    # handled separately
    ################################################################################
    first=${@:1:1}
    last=${ @:$#:1}
    len=$(($#-2))
    inputs=${@:2:$len}
    
    # remove all previous tmp fifos (if exist)
    rm -f $TMP/mcs_*
    
    ################################################################################
    # decode first input differently, because the video header does not have to be
    # kept for each video input, only the header from the first video is needed
    ################################################################################
    mkfifo $TMP/mcs_a1 $TMP/mcs_v1
    
    ffmpeg -y -i $first -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 $TMP/mcs_a1 2>/dev/null </dev/null &
    ffmpeg -y -i $first -an -f yuv4mpegpipe -vcodec rawvideo $TMP/mcs_v1 2>/dev/null </dev/null &
    
    # if you need to log the output of decoding processes (usually not necessary)
    # then replace the "2>/dev/null" in 2 lines above with your log file names, like this:
    #ffmpeg -y -i $first -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 $TMP/mcs_a1 2>$TMP/log.a.1 </dev/null &
    #ffmpeg -y -i $first -an -f yuv4mpegpipe -vcodec rawvideo $TMP/mcs_v1 2>$TMP/log.v.1 </dev/null &
    
    ################################################################################
    # decode all the other inputs, remove first line of video (header) with tail
    # $all_a and $all_v are lists of all a/v fifos, to be used by "cat" later on
    ################################################################################
    all_a=$TMP/mcs_a1
    all_v=$TMP/mcs_v1
    i=2
    for f in $inputs
    do
    	mkfifo $TMP/mcs_a$i $TMP/mcs_v$i
    
    	ffmpeg -y -i $f -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 $TMP/mcs_a$i 2>/dev/null </dev/null &
    	{  ffmpeg -y -i $f -an -f yuv4mpegpipe -vcodec rawvideo - 2>/dev/null </dev/null | tail -n +2 > $TMP/mcs_v$i ; } &
    
    	# if you need to log the output of decoding processes (usually not necessary)
    	# then replace the "2>/dev/null" in 2 lines above with your log file names, like this:
    	#ffmpeg -y -i $f -vn -f u16le -acodec pcm_s16le -ac 2 -ar 44100 $TMP/mcs_a$i 2>$TMP/log.a.$i </dev/null &
    	#{ ffmpeg -y -i $f -an -f yuv4mpegpipe -vcodec rawvideo - 2>$TMP/log.v.$i </dev/null | tail -n +2 > $TMP/mcs_v$i ; } &
    
    	all_a="$all_a $TMP/mcs_a$i"
    	all_v="$all_v $TMP/mcs_v$i"
    	let i++
    done
    
    ################################################################################
    # concatenate all raw audio/video inputs into one audio/video
    ################################################################################
    mkfifo $TMP/mcs_a_all
    mkfifo $TMP/mcs_v_all
    cat $all_a > $TMP/mcs_a_all &
    cat $all_v > $TMP/mcs_v_all &
    
    ################################################################################
    # finally, encode the raw concatenated audio/video into something useful
    ################################################################################
    ffmpeg -f u16le -acodec pcm_s16le -ac 2 -ar 44100 -i $TMP/mcs_a_all \
           -f yuv4mpegpipe -vcodec rawvideo -i $TMP/mcs_v_all \
    	$EXTRA_OPTIONS \
    	$last
    
    ################################################################################
    # remove all fifos
    ################################################################################
    rm -f $TMP/mcs_*