clarifications

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Andrew Weaver 2019-01-02 19:23:18 -08:00
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<dt>ffplay</dt><dd>starts the command</dd>
<dt>-f lavfi -i testsrc</dt><dd>tells ffplay to use the <a href="https://ffmpeg.org/ffmpeg-devices.html#lavfi" target="_blank">Libavfilter's virtual device input 'testsrc'</a></dd>
<dt>-vf</dt><dd>tells ffmpeg that you will be applying a filter chain to the input</dd>
<dt>split=3[a][b][c],</dt><dd>splits the input into three separate signals within the filter graph, named a, b and c respectively. The <code>,</code> separates this from the next part of the filter chain.
<dt>split=3[a][b][c],</dt><dd>splits the input into three separate signals within the filter graph, named a, b and c respectively. (These are variables and any names could be used as long as they are kept consistent in following steps). The <code>,</code> separates this from the next part of the filter chain.
<dt>[a][b][c]xstack=inputs=3:</dt><dd>tells ffmpeg that you will be using the xstack filter on the three named inputs a,b and c. The final <code>:</code> is a necessary divider between the number of inputs, and the orientation of outputs portion of the xstack command.</dd>
<dt>layout=0_0|0_h0|0_h0+h1</dt><dd>This is where the locations of the video sources in the ouput stack are designated. The locations are specified in order of input (so in this example <code>0_0</code> corresponds to input <code>[a]</code>. Inputs must be separated with a <code>|</code>. The two numbers represent columns and rows, with counting starting at zero rather than one. In this example, <code>0_0</code> means that input <code>[a]</code> is placed at the first row of the first column in the output. <code>0_h0</code> places the next input in the first column, at a row corresponding with the height of the first input. <code>0_h0+h1</code> places the final input in the first column, at a row corresponding with the height of the first input plus the height of the second input. This has the effect of creating a vertical stack of the three inputs. This could be made a horizontal stack by changing this portion of the command to <code>layout=0_0|w0_0|w0+w1_0</code>.</dd>
<dt>layout=0_0|0_h0|0_h0+h1</dt><dd>This is where the locations of the video sources in the output stack are designated. The locations are specified in order of input (so in this example <code>0_0</code> corresponds to input <code>[a]</code>. Inputs must be separated with a <code>|</code>. The two numbers represent columns and rows, with counting starting at zero rather than one. In this example, <code>0_0</code> means that input <code>[a]</code> is placed at the first row of the first column in the output. <code>0_h0</code> places the next input in the first column, at a row corresponding with the height of the first input. <code>0_h0+h1</code> places the final input in the first column, at a row corresponding with the height of the first input plus the height of the second input. This has the effect of creating a vertical stack of the three inputs. This could be made a horizontal stack by changing this portion of the command to <code>layout=0_0|w0_0|w0+w1_0</code>.</dd>
<dt>[out]</dt><dd>this ends the filter chain and designates the final output.</dd>
</dl>
<div class="sample-image">