Merge pull request #166 from kfrn/gh-pages

Add more detail to H.264 and GIF commands

index.html

@@ -153,9 +153,12 @@
           <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>
           <p class="link"></p>
         </div>
       </div>
@@ -384,7 +387,7 @@
         <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>
@@ -812,16 +815,25 @@
           <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>
           <p class="link"></p>
         </div>
       </div>
@@ -1408,6 +1420,29 @@ foreach ($file in $inputfiles) {
   </div>
   <!-- ends Play VGA SMPTE bars -->
 
+  <!-- Broken File -->
+  <span data-toggle="modal" data-target="#broken_file"><button type="button" class="btn btn-default" data-toggle="tooltip" data-placement="bottom" title="Make a broken file out of a perfectly good one">Broken file</button></span>
+  <div id="broken_file" class="modal fade" tabindex="-1" role="dialog">
+    <div class="modal-dialog modal-lg">
+      <div class="modal-content">
+        <div class="well">
+          <h3>Makes a broken test file</h3>
+          <p>Modifies an existing, functioning file and intentionally breaks it for testing purposes.</p>
+          <p><code>ffmpeg -i <i>input_file</i> -bsf noise=1 -c copy <i>output_file</i></code></p>
+          <dl>
+            <dt>ffmpeg</dt><dd>starts the command</dd>
+            <dt>-i <i>input_file</i></dt><dd>takes in a normal file</dd>
+            <dt>-bsf noise=1</dt><dd>sets bitstream filters for all to 'noise'. Filters can be set on specific filters using syntax such as <code>-bsf:v</code> for video, <code>-bsf:a</code> for audio, etc. The <a target="_blank" href="https://www.ffmpeg.org/ffmpeg-bitstream-filters.html#noise">noise filter</a> intentionally damages the contents of packets without damaging the container. This sets the noise level to 1 but it could be left blank or any number above 0.</dd>
+            <dt>-c copy</dt><dd>use stream copy mode to re-mux instead of re-encode</dd>
+            <dt><i>output_file</i></dt><dd>path, name and extension of the output file</dd>
+          </dl>
+          <p class="link"></p>
+        </div>
+      </div>
+    </div>
+  </div>
+  <!-- ends Broken File -->
+
   <!-- Sine wave -->
   <span data-toggle="modal" data-target="#sine_wave"><button type="button" class="btn btn-default" data-toggle="tooltip" data-placement="bottom" title="Generate a test audio file playing a sine wave">Sine wave</button></span>
   <div id="sine_wave" class="modal fade" tabindex="-1" role="dialog">