我想将视频尺寸缩小到 720:480 并保持原始宽高比，当输入视频宽度 > 720 时，否则保持原始尺寸和宽高比。
我尝试在 Windows 批处理文件中重现此脚本但失败了：
使用 ffmpeg/avconv 调整视频大小以适合静态大小的播放器
set $width=720
set $height=480
ffmpeg -i file8.3gp -vcodec libx264 -preset slow -crf 20 -filter:v "scale=iw*min($width/iw,$height/ih):ih*min($width/iw,$height/ih), pad=$width:$height:($width-iw*min($width/iw,$height/ih))/2:($height-ih*min($width/iw,$height/ih))/2" -threads 0 -acodec libvo_aacenc -b:a 128k out.mp4
我收到的错误：
ffmpeg -i file8.3gp -vcodec libx264 -preset slow
-crf 20 -filter:v "scale=iw*min($width/iw,$height/ih):ih*min($width/iw,$height/i
h), pad=$width:$height:($width-iw*min($width/iw,$height/ih))/2:($height-ih*min($
width/iw,$height/ih))/2" -threads 0 -acodec libvo_aacenc -b:a 128k out.mp4
ffmpeg version N-54691-g7f4a1fd Copyright (c) 2000-2013 the FFmpeg developers
built on Jul 12 2013 16:31:48 with gcc 4.7.3 (GCC)
configuration: --enable-gpl --enable-version3 --disable-w32threads --enable-av
isynth --enable-bzlib --enable-fontconfig --enable-frei0r --enable-gnutls --enab
le-iconv --enable-libass --enable-libbluray --enable-libcaca --enable-libfreetyp
e --enable-libgsm --enable-libilbc --enable-libmodplug --enable-libmp3lame --ena
ble-libopencore-amrnb --enable-libopencore-amrwb --enable-libopenjpeg --enable-l
ibopus --enable-librtmp --enable-libschroedinger --enable-libsoxr --enable-libsp
eex --enable-libtheora --enable-libtwolame --enable-libvo-aacenc --enable-libvo-
amrwbenc --enable-libvorbis --enable-libvpx --enable-libx264 --enable-libxavs --
enable-libxvid --enable-zlib
libavutil 52. 39.100 / 52. 39.100
libavcodec 55. 18.102 / 55. 18.102
libavformat 55. 12.102 / 55. 12.102
libavdevice 55. 3.100 / 55. 3.100
libavfilter 3. 80.101 / 3. 80.101
libswscale 2. 3.100 / 2. 3.100
libswresample 0. 17.102 / 0. 17.102
libpostproc 52. 3.100 / 52. 3.100
Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'file8.3gp':
Metadata:
major_brand : 3gp5
minor_version : 256
compatible_brands: 3gp53gp4
creation_time : 2005-10-28 17:36:40
Duration: 00:00:04.93, start: 0.000000, bitrate: 46 kb/s
Stream #0:0(eng): Audio: amr_nb (samr / 0x726D6173), 8000 Hz, mono, flt, 8 k
b/s
Metadata:
creation_time : 2005-10-28 17:36:40
handler_name : Apple Sound Media Handler
Stream #0:1(eng): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p
, 176x144 [SAR 1:1 DAR 11:9], 35 kb/s, 15 fps, 15 tbr, 600 tbn, 1k tbc
Metadata:
creation_time : 2005-10-28 17:36:40
handler_name : Apple Video Media Handler
File 'out.mp4' already exists. Overwrite ? [y/N] y
[Parsed_scale_0 @ 0000000000318640] Invalid size 'iw*min($width/iw'
[AVFilterGraph @ 00000000024c0540] Error initializing filter 'scale' with args '
iw*min($width/iw:flags=0x4'
Error opening filters!
答案1
我的机器上没有这个ffmpeg，所以我无法测试这个，但是从命令提示符不使用美元符号的观察开始，我应用了以下转换：
- 改成。
set $var=$valueset var=$value - 改成。
$var%var%
我恢复了slhck♦ 的回答，我想到了：
@echo off set width=720 set height=480
ffmpeg -i file8.3gp -vcodec libx264 -preset slow -crf 20 -filter:v "scale=iw*min(%width%/iw\,%height%/ih):ih*min(%width%/iw\,%height%/ih), pad=%width%:%height%:(%width%-iw*min(%width%/iw\,%height%/ih))/2:(%height%-ih*min(%width%/iw\,%height%/ih))/2" -threads 0 -acodec libvo_aacenc -b:a 128k out.mp4
（为清楚起见添加了空行。）为了进一步清楚，你可以将该长行拆分成如下形式：
ffmpeg -i file8.3gp -vcodec libx264 -preset slow -crf 20 -filter:v ^ "scale=iw*min(%width%/iw\,%height%/ih):ih*min(%width%/iw\,%height%/ih), pad=%width%:%height%:(%width%-iw*min(%width%/iw\,%height%/ih))/2:(%height%-ih*min(%width%/iw\,%height%/ih))/2" ^ -threads 0 -acodec libvo_aacenc -b:a 128k out.mp4
我不确定你是否可以在引号字符串中做到这一点。祝你好运！