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Merge pull request #166 from kfrn/gh-pages

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Add more detail to H.264 and GIF commands
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Reto Kromer 2017-03-31 09:40:39 +02:00 committed by GitHub
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<p>In order to use the same basic command to make a higher quality file, you can add some of these presets:</p>
<p><code>ffmpeg -i <i>input_file</i> -c:v libx264 -pix_fmt yuv420p -preset veryslow -crf 18 -c:a copy <i>output_file</i></code></p>
<dl>
<dt>-preset <i>veryslow</i></dt><dd>This option tells ffmpeg to use the slowest preset possible for the best compression quality.</dd>
<dt>-crf <i>18</i></dt><dd>Specifying a lower CRF will make a larger file with better visual quality. 18 is often considered a “visually lossless” compression.</dd>
<dt>-preset <i>veryslow</i></dt><dd>This option tells ffmpeg to use the slowest preset possible for the best compression quality.<br>
Available presets, from slowest to fastest, are: <code>veryslow</code>, <code>slower</code>, <code>slow</code>, <code>medium</code>, <code>fast</code>, <code>faster</code>, <code>veryfast</code>, <code>superfast</code>, <code>ultrafast</code>.</dd>
<dt>-crf <i>18</i></dt><dd>Specifying a lower CRF will make a larger file with better visual quality. For H.264 files being encoded with a 4:2:0 chroma subsampling scheme (i.e., using <code>-pix_fmt yuv420p</code>), the scale ranges between 0-51, with 0 being lossless and 51 the worst possible quality.<br>
If no crf is specified, <code>libx264</code> will use a default value of 23. 18 is often considered a “visually lossless” compression.</dd>
</dl>
<p>For more information, see the <a href="https://trac.ffmpeg.org/wiki/Encode/H.264" target="_blank">FFmpeg and H.264 Encoding Guide</a> on the ffmpeg wiki.</p>
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<div class="well">
<h3>Images to GIF</h3>
<p><code>ffmpeg -f image2 -framerate 9 -pattern_type glob -i <i>"input_image_*.jpg"</i> -vf scale=250x250 <i>output_file</i>.gif</code></p>
<p>This will convert a series of image files into a gif.</p>
<p>This will convert a series of image files into a GIF.</p>
<dl>
<dt>ffmpeg</dt><dd>starts the command</dd>
<dt>-f image2</dt><dd>forces input or output file format. <code>image2</code> specifies the image file demuxer.</dd>
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<p>The first command will use the palettegen filter to create a custom palette, then the second command will create the GIF with the paletteuse filter. The result is a high quality GIF.</p>
<dl>
<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>-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>-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>
<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>
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