Changes between Version 1 and Version 2 of Option '-sameq' does NOT mean 'same quality'


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Timestamp:
Oct 20, 2012, 10:02:47 PM (4 years ago)
Author:
cbsrobot
Comment:

specify the usage only for the same format

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  • Option '-sameq' does NOT mean 'same quality'

    v1 v2  
    44The purpose of this article is to draw attention to the fact that many users believe that FFmpeg's option named "-sameq" actually means "same quality" (in order to keep the quality of the output video the same as the quality of the input video), which is not true. 
    55 
    6 This option actually means "same quantizers". The option name was poorly/quickly chosen, which created all the mess afterwards. Even the documentation, in one moment, was stating that: "Note that this is NOT SAME QUALITY. Do not use this option unless you know you need it". 
     6This option actually means "same quantizers" and should only be used to copy the quants from the input to the output of the same format (f.ex. mpeg2 -> mpeg2). The option name was poorly/quickly chosen, which created a mess afterwards. Even the documentation, in one moment, was stating that: "Note that this is NOT SAME QUALITY. Do not use this option unless you know you need it". 
    77 
    88Shortly, don't use the "-sameq" option if you want to "just keep the quality of the input video". What you really want is to understand that not all the video encoders have one universal way to copy the original video's quality. It's similar if you would like to unzip a text file, change the text ("just a little bit") inside a file and zip it again, expecting the file size to remain the same. That's just not how things work.