fixes #475 (#476)

Clarification of documentation

index.html

@@ -47,11 +47,11 @@
       <h2 class="heading" id="about">About ffmprovisr</h2>
       <h3>Making FFmpeg Easier</h3>
       <p>FFmpeg is a powerful tool for manipulating audiovisual files. Unfortunately, it also has a steep learning curve, especially for users unfamiliar with a command line interface. This app helps users through the command generation process so that more people can reap the benefits of FFmpeg.</p>
-      <p>Each button displays helpful information about how to perform a wide variety of tasks using FFmpeg. To use this site, click on the task you would like to perform. A new window will open up with a sample command and a description of how that command works. You can copy this command and understand how the command works with a breakdown of each of the flags.</p>
+      <p>Each button displays helpful information about how to perform a wide variety of tasks using FFmpeg. To use this site, click on the task you would like to perform. You will jump to a single command or a list of related commands. Click on a command description, and the site will display a sample command as well as an explanation of how that command works with a breakdown of each of its flags (or options).</p>
       <p>This page does not have search functionality, but you can open all recipes (second option in the sidebar) and use your browser's search tool (often ctrl+f or cmd+f) to perform a keyword search through all recipes.</p>
       <h3>Tutorials</h3>
       <p>For FFmpeg basics, check out the program’s <a href="https://ffmpeg.org/" target="_blank">official website</a>.</p>
-      <p>For instructions on how to install FFmpeg on Mac, Linux, and Windows, refer to Reto Kromer’s <a href="https://avpres.net/FFmpeg/#ch1" target="_blank">installation instructions</a>.</p>
+      <p>For instructions on how to install FFmpeg on macOS, Linux, and Windows, refer to Reto Kromer’s <a href="https://avpres.net/FFmpeg/#ch1" target="_blank">installation instructions</a>.</p>
       <p>For Bash and command line basics, try the <a href="https://learnpythonthehardway.org/book/appendixa.html" target="_blank">Command Line Crash Course</a>. For a little more context presented in an ffmprovisr style, try <a href="https://explainshell.com/" target="_blank">explainshell.com</a>!</p>
       <h3>License</h3>
       <p class="license">
@@ -225,7 +225,7 @@
         The new container you are rewrapping to is defined by the filename extension used here, e.g. .mkv, .mp4, .mov.</dd>
       </dl>
       <h4>Important caveat</h4>
-      <p>It may not be possible to rewrap a file's contents to a new container without re-encoding one or more of the streams within (that is, the video, audio, and subtitle tracks). Some containers can only contain streams of a certain encoding type: for example, the .mp4 container does not support uncompressed audio tracks. (In practice .mp4 goes hand-in-hand with a H.264-encoded video stream and an AAC-encoded video stream, although other types of video and audio streams are possible). Another example is that the Matroska container does not allow data tracks; see the <a href="#mkv-to-mp4">MKV to MP4 recipe</a>.</p>
+      <p>It may not be possible to rewrap a file's contents to a new container without re-encoding one or more of the streams within (that is, the video, audio, and subtitle tracks). Some containers can only contain streams of a certain encoding type: for example, the .mp4 container does not support uncompressed audio tracks. (In practice .mp4 goes hand-in-hand with a H.264-encoded video stream and an AAC-encoded video stream, although other types of video and audio streams are possible). Another example is that the Matroska container does not allow data tracks.</p>
       <p>In such cases, FFmpeg will throw an error. If you encounter errors of this kind, you may wish to consult the <a href="#transcode">list of transcoding recipes</a>.</p>
       <p class="link"></p>
     </div>
@@ -680,22 +680,23 @@
     </div>
     <!-- ends SD to HD -->
 
-    <!-- Change display aspect ratio without re-encoding video-->
+    <!-- Change display aspect ratio without re-encoding -->
     <label class="recipe" for="change_DAR">Change display aspect ratio without re-encoding</label>
     <input type="checkbox" id="change_DAR">
     <div class="hiding">
-      <h5>Change Display Aspect Ratio without re-encoding video</h5>
-      <p><code>ffmpeg -i <em>input_file</em> -c:v copy -aspect 4:3 <em>output_file</em></code></p>
+      <h5>Change Display Aspect Ratio without re-encoding</h5>
+      <p><code>ffmpeg -i <em>input_file</em> -c:a copy -c:v copy -aspect 4:3 <em>output_file</em></code></p>
       <dl>
         <dt>ffmpeg</dt><dd>starts the command</dd>
         <dt>-i <em>input_file</em></dt><dd>path, name and extension of the input file</dd>
+        <dt>-c:a copy</dt><dd>Copy all mapped audio streams.</dd>
         <dt>-c:v copy</dt><dd>Copy all mapped video streams.</dd>
         <dt>-aspect 4:3</dt><dd>Change Display Aspect Ratio to <code>4:3</code>. Experiment with other aspect ratios such as <code>16:9</code>. If used together with <code>-c:v copy</code>, it will affect the aspect ratio stored at container level, but not the aspect ratio stored in encoded frames, if it exists.</dd>
         <dt><em>output_file</em></dt><dd>path, name and extension of the output file</dd>
       </dl>
       <p class="link"></p>
     </div>
-    <!-- ends Change display aspect ratio without re-encoding video -->
+    <!-- ends Change display aspect ratio without re-encoding -->
 
     <!-- Convert colorspace -->
     <label class="recipe" for="convert-colorspace">Convert colorspace of video</label>
@@ -1409,6 +1410,43 @@
     </div>
     <!-- ends Deinterlace video -->
 
+    <!-- Deinterlace video fields -->
+    <label class="recipe" for="deinterlace_fields">Deinterlace video fields to frames</label>
+    <input type="checkbox" id="deinterlace_fields">
+    <div class="hiding">
+      <h5>Deinterlace video fields to frames</h5>
+      <p><code>ffmpeg -i <em>input_file</em> -c:v libx264 -vf "idet,bwdif,format=yuv420p" <em>output_file</em></code></p>
+      <p>This command takes an interlaced input file and outputs a deinterlaced H.264 MP4, with each field separated into its own frame.  This is preferred for interlaced video that contains a lot of motion, as the double-rate output preserves the visual cadence of the source material.</p>
+      <dl>
+        <dt>ffmpeg</dt><dd>starts the command</dd>
+        <dt>-i <em>input file</em></dt><dd>path, name and extension of the input file</dd>
+        <dt>-c:v libx264</dt><dd>tells FFmpeg to encode the video stream as H.264</dd>
+        <dt>-vf</dt><dd>video filtering will be used (<code>-vf</code> is an alias of <code>-filter:v</code>)</dd>
+        <dt>"</dt><dd>start of filtergraph (see below)</dd>
+        <dt>idet</dt><dd>detect interlaced video field order<br>
+         <a href="https://ffmpeg.org/ffmpeg-filters.html#idet" target="_blank">idet</a> will try to detect if the video is interlaced, and if so, what the order of the fields are (top-field-first, or bottom-field-first).  This is done to ensure the output of the deinterlacing filter is correct.</dd>
+        <dt>bwdif</dt><dd>deinterlacing filter (‘Bob Weaver Deinterlacing Filter’)<br>
+         By default, <a href="https://ffmpeg.org/ffmpeg-filters.html#bwdif-1" target="_blank">bwdif</a> will output one frame for each field, matching the visual cadence of interlaced video. </dd>
+        <dt>,</dt><dd>separates filters</dd>
+        <dt>format=yuv420p</dt><dd>chroma subsampling set to 4:2:0<br>
+        By default, <code>libx264</code> will use a chroma subsampling scheme that is the closest match to that of the input. This can result in Y′C<sub>B</sub>C<sub>R</sub> 4:2:0, 4:2:2, or 4:4:4 chroma subsampling. QuickTime and most other non-FFmpeg based players can’t decode H.264 files that are not 4:2:0, therefore it’s advisable to specify 4:2:0 chroma subsampling.</dd>
+        <dt>"</dt><dd>end of filtergraph</dd>
+        <dt><em>output file</em></dt><dd>path, name and extension of the output file</dd>
+      </dl>
+      <p><code>"idet,bwdif,format=yuv420p"</code> is an FFmpeg <a href="https://trac.ffmpeg.org/wiki/FilteringGuide#FiltergraphChainFilterrelationship" target="_blank">filtergraph</a>. Here the filtergraph is made up of one filter chain, which is itself made up of the three filters (separated by the comma).<br>
+      The enclosing quote marks are necessary when you use spaces within the filtergraph, e.g. <code>-vf "idet, bwdif, format=yuv420p"</code>, and are included above as an example of good practice.</p>
+      <p><strong>Note:</strong> bwdif also supports the older method of outputting one frame for each frame (thereby halving the number of output frames per second) with the syntax <code>bwdif=mode=send_frame</code>.  This can be used when the presentation device is not capable of reproducing 50 (PAL) or 60 (NTSC) frames per second.</p>
+      <p>For more H.264 encoding options, see the latter section of the <a href="#transcode_h264">encode H.264 command</a>.</p>
+      <div class="sample-image">
+        <h2>Example</h2>
+        <p>Before and after deinterlacing with bwdif:</p>
+        <img src="img/interlaced_video_fields.png" alt="VLC screenshot of original interlaced video">
+        <img src="img/deinterlaced_video_frames.png" alt="VLC screenshot of deinterlaced video">
+      </div>
+      <p class="link"></p>
+    </div>
+    <!-- ends Deinterlace video fields -->
+
     <!-- Inverse telecine -->
     <label class="recipe" for="inverse-telecine">Inverse telecine</label>
     <input type="checkbox" id="inverse-telecine">

recipes.txt

@@ -37,7 +37,7 @@ ffmpeg -i input_file -filter:v "hflip,vflip" -c:a copy output_file
 # Transform SD to HD with pillarbox
 ffmpeg -i input_file -filter:v "colormatrix=bt601:bt709, scale=1440:1080:flags=lanczos, pad=1920:1080:240:0" -c:a copy output_file
 # Change display aspect ratio without re-encoding
-ffmpeg -i input_file -c:v copy -aspect 4:3 output_file
+ffmpeg -i input_file -c:a copy -c:v copy -aspect 4:3 output_file
 # Convert colorspace of video
 ffmpeg -i input_file -c:v libx264 -vf colormatrix=src:dst output_file
 # Modify image and sound speed
@@ -92,6 +92,8 @@ ffmpeg -i input_file -af areverse,silenceremove=start_threshold=-57dB:start_dura
 ffmpeg -i input_file -c:v libx264 -filter:v "yadif, scale=1440:1080:flags=lanczos, pad=1920:1080:(ow-iw)/2:(oh-ih)/2, format=yuv420p" output_file
 # Deinterlace video
 ffmpeg -i input_file -c:v libx264 -vf "yadif,format=yuv420p" output_file
+# Deinterlace video fields to frames
+ffmpeg -i input_file -c:v libx264 -vf "idet,bwdif,format=yuv420p" output_file
 # Inverse telecine
 ffmpeg -i input_file -c:v libx264 -vf "fieldmatch,yadif,decimate" output_file
 # Set field order for interlaced video