ffmpeg調整大小保持方面 - 未找到過濾器

Question

我試圖創建圖像縮略圖，以保持原始的方面，但如果尺寸太大，則裁剪它。 發現了一個可能的代碼片斷here

ffmpeg -i Einstein_500_459.jpg -vf scale="'if(gt(a,320/240),320,-1)':'if(gt(a,320/240),-1,240)'" Einstein_320x240_fit.png 

，但不能得到的ffmpeg來執行它。逃逸單引號

ffmpeg -i Einstein_500_459.jpg -vf scale="\'if(gt(a,320/240),320,-1)\':\'if(gt(a,320/240),-1,240)\'" Einstein_320x240_fit.png 

後

ffmpeg -i Einstein_500_459.jpg -vf scale="'if(gt(a,320/240),320,-1)':'if(gt(a,320/240),-1,240)'" Einstein_320x240_fit.png 
ffmpeg version 0.10.12-7:0.10.12-1~precise1 Copyright (c) 2000-2014 the FFmpeg developers 
    built on Apr 26 2014 09:49:36 with gcc 4.6.3 
    configuration: --arch=amd64 --disable-stripping --enable-pthreads --enable-runtime-cpudetect --extra-version='7:0.10.12-1~precise1' --libdir=/usr/lib/x86_64-linux-gnu --prefix=/usr --enable-bzlib --enable-libdc1394 --enable-libfreetype --enable-frei0r --enable-gnutls --enable-libgsm --enable-libmp3lame --enable-librtmp --enable-libopencv --enable-libopenjpeg --enable-libpulse --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-vaapi --enable-vdpau --enable-libvorbis --enable-libvpx --enable-zlib --enable-gpl --enable-postproc --enable-libcdio --enable-x11grab --enable-libx264 --shlibdir=/usr/lib/x86_64-linux-gnu --enable-shared --disable-static 
    libavutil  51. 35.100/51. 35.100 
    libavcodec  53. 61.100/53. 61.100 
    libavformat 53. 32.100/53. 32.100 
    libavdevice 53. 4.100/53. 4.100 
    libavfilter  2. 61.100/2. 61.100 
    libswscale  2. 1.100/2. 1.100 
    libswresample 0. 6.100/0. 6.100 
    libpostproc 52. 0.100/52. 0.100 
Input #0, image2, from 'Einstein_500_459.jpg': 
    Duration: 00:00:00.04, start: 0.000000, bitrate: N/A 
    Stream #0:0: Video: mjpeg, yuvj444p, 500x459 [SAR 300:300 DAR 500:459], 25 tbr, 25 tbn, 25 tbc 
Incompatible pixel format 'yuvj444p' for codec 'png', auto-selecting format 'rgb24' 
[buffer @ 0x236d720] w:500 h:459 pixfmt:yuvj444p tb:1/1000000 sar:300/300 sws_param: 
[scale @ 0x235d5e0] [Eval @ 0x7fffcb68f270] Missing ')' or too many args in 'if(gt(a,320/240),320,-1)' 
[scale @ 0x235d5e0] [Eval @ 0x7fffcb68f270] Missing ')' or too many args in 'if(gt(a,320/240),-1,240)' 
Error when evaluating the expression 'if(gt(a,320/240),-1,240)'. 
Maybe the expression for out_w:'if(gt(a,320/240),320,-1)' or for out_h:'if(gt(a,320/240),-1,240)' is self-referencing. 
Error opening filters! 

它生成錯誤

ffmpeg -i Einstein_500_459.jpg -vf scale="\'if(gt(a,320/240),320,-1)\':\'if(gt(a,320/240),-1,240)\'" Einstein_320x240_fit.png 
ffmpeg version 0.10.12-7:0.10.12-1~precise1 Copyright (c) 2000-2014 the FFmpeg developers 
    built on Apr 26 2014 09:49:36 with gcc 4.6.3 
    configuration: --arch=amd64 --disable-stripping --enable-pthreads --enable-runtime-cpudetect --extra-version='7:0.10.12-1~precise1' --libdir=/usr/lib/x86_64-linux-gnu --prefix=/usr --enable-bzlib --enable-libdc1394 --enable-libfreetype --enable-frei0r --enable-gnutls --enable-libgsm --enable-libmp3lame --enable-librtmp --enable-libopencv --enable-libopenjpeg --enable-libpulse --enable-libschroedinger --enable-libspeex --enable-libtheora --enable-vaapi --enable-vdpau --enable-libvorbis --enable-libvpx --enable-zlib --enable-gpl --enable-postproc --enable-libcdio --enable-x11grab --enable-libx264 --shlibdir=/usr/lib/x86_64-linux-gnu --enable-shared --disable-static 
    libavutil  51. 35.100/51. 35.100 
    libavcodec  53. 61.100/53. 61.100 
    libavformat 53. 32.100/53. 32.100 
    libavdevice 53. 4.100/53. 4.100 
    libavfilter  2. 61.100/2. 61.100 
    libswscale  2. 1.100/2. 1.100 
    libswresample 0. 6.100/0. 6.100 
    libpostproc 52. 0.100/52. 0.100 
Input #0, image2, from 'Einstein_500_459.jpg': 
    Duration: 00:00:00.04, start: 0.000000, bitrate: N/A 
    Stream #0:0: Video: mjpeg, yuvj444p, 500x459 [SAR 300:300 DAR 500:459], 25 tbr, 25 tbn, 25 tbc 
Incompatible pixel format 'yuvj444p' for codec 'png', auto-selecting format 'rgb24' 
[buffer @ 0x1897720] w:500 h:459 pixfmt:yuvj444p tb:1/1000000 sar:300/300 sws_param: 
No such filter: '320/240)' 
Error opening filters! 

這只是一個語法問題：因爲它是在終端產生錯誤？或者是我的ffmpeg錯過了什麼？或者是什麼？ 這是Ubuntu 12.04與我相信是完全安裝ffmpeg，而不是libav默認的東西。任何幫助表示讚賞。

Answer 1

解決的辦法是安裝最新的ffmpeg，對於任何有此問題的人。

ffmpeg -i Einstein_500_459.jpg -vf scale="'if(gt(a,320/240),320,-1)':'if(gt(a,320/240),-1,240)'" Einstein_320x240_fit.png 

這段代碼的工作沒有問題，在Ubuntu 12.04 - ffmpeg的版本：2.8.3

有一個腳本編譯在Ubuntu 12.04或14.04 HERE