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Add more explanation to GIF creation command

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kfrn 2017-03-31 17:15:24 +13:00
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<dt>ffmpeg</dt><dd>starts the command</dd>
<dt>-ss <i>HH:MM:SS</i></dt><dd>starting point of the gif. If a plain numerical value is used it will be interpreted as seconds</dd>
<dt>-i <i>input_file</i></dt><dd>path, name and extension of the input file</dd>
<dt>-filter_complex "fps=<i>frame rate</i>,scale=<i>width</i>:<i>height</i>,palettegen"</dt><dd>a complex filtergraph using the fps filter to set frame rate, the scale filter to resize, and the palettegen filter to generate the palette. The scale value of <i>-1</i> preserves the aspect ratio</dd>
<dt>-filter_complex "fps=<i>frame rate</i>,scale=<i>width</i>:<i>height</i>,palettegen"</dt><dd>a complex filtergraph.<br>
Firstly, the fps filter sets the frame rate.<br>
Then the scale filter resizes the image. You can specify both the width and the height, or specify a value for one and use a scale value of <i>-1</i> for the other to preserve the aspect ratio. (For example, <code>500:-1</code> would create a GIF 500 pixels wide and with a height proportional to the original video). In the first script above, <code>:flags:lanczos</code> specifies that the Lanczos rescaling algorithm will be used to resize the image.<br>
Lastly, the palettegen filter generates the palette.</dd>
<dt>-t <i>3</i></dt><dd>duration in seconds (here 3; can be specified also with a full timestamp, i.e. here 00:00:03)</dd>
<dt>-loop <i>6</i></dt><dd>number of times to loop the gif. A value of <i>-1</i> will disable looping. Omitting <i>-loop</i> will use the default which will loop infinitely</dd>
<dt><i>output_file</i></dt><dd>path, name and extension of the output file</dd>
</dl>
<p>The second command has a slightly different filtergraph, which breaks down as follows:</p>
<dl>
<dt>-filter_complex "[0:v]fps=10,scale=500:-1:flags=lanczos[v],[v][1:v]paletteuse"</dt><dd>
<code>[0:v]fps=10,scale=500:-1:flags=lanczos[v]</code>: applies the fps and scale filters described above to the first input file (the video).<br>
<code>[v][1:v]paletteuse"</code>: applies the <code>paletteuse</code> filter, setting the second input file (the palette) as the reference file.</dd>
</dl>
<p>Simpler GIF creation</p>
<p><code>ffmpeg -ss HH:MM:SS -i <i>input_file</i> -vf "fps=10,scale=500:-1" -t 3 -loop 6 <i>output_file</i></code></p>
<p>This is a quick and easy method. Dithering is more apparent than the above method using the palette filters, but the file size will be smaller. Perfect for that “legacy” GIF look.</p>