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<h1>Decode With Drops Example</h1>

This is an example utility which drops a series of frames, as specified
on the command line. This is useful for observing the error recovery
features of the codec.

<h2>Usage</h2>

This example adds a single argument to the <code>simple_decoder</code> example,
which specifies the range or pattern of frames to drop. The parameter is
parsed as follows:

<pre class="c">if&#40;argc!=4&#41;
 die&#40;&quot;Usage: %s &lt;infile&gt; &lt;outfile&gt; &lt;N-M|N/M&gt;\n&quot;, argv&#91;0&#93;&#41;;
&#123;
 char *nptr;
 n = strtol&#40;argv&#91;3&#93;, &amp;nptr, 0&#41;;
 m = strtol&#40;nptr+1, NULL, 0&#41;;
 is_range = *nptr == '-';
 if&#40;!n || !m || &#40;*nptr != '-' &amp;&amp; *nptr != '/'&#41;&#41;
 die&#40;&quot;Couldn't parse pattern %s\n&quot;, argv&#91;3&#93;&#41;;
&#125;</pre>

<h2>Dropping A Range Of Frames</h2>

To drop a range of frames, specify the starting frame and the ending
frame to drop, separated by a dash. The following command will drop
frames 5 through 10 (base 1).

$ ./decode_with_drops in.ivf out.i420 5-10

<h2>Dropping A Pattern Of Frames</h2>

To drop a pattern of frames, specify the number of frames to drop and
the number of frames after which to repeat the pattern, separated by
a forward-slash. The following command will drop 3 of 7 frames.
Specifically, it will decode 4 frames, then drop 3 frames, and then
repeat.

$ ./decode_with_drops in.ivf out.i420 3/7

<h2>Extra Variables</h2>

This example maintains the pattern passed on the command line in the
<code>n</code>, <code>m</code>, and <code>is_range</code> variables:

<pre class="c">int n, m, is_range;</pre>

<h2>Making The Drop Decision</h2>

The example decides whether to drop the frame based on the current
frame number, immediately before decoding the frame.

<pre class="c">if&#40;&#40;is_range &amp;&amp; frame_cnt &gt;= n &amp;&amp; frame_cnt &lt;= m&#41;
 ||&#40;!is_range &amp;&amp; m - &#40;frame_cnt-1&#41;%m &lt;= n&#41;&#41; &#123;
 putc&#40;'X', stdout&#41;;
 continue;
&#125;
putc&#40;'.', stdout&#41;;
fflush&#40;stdout&#41;;</pre>

<h1>Putting It All Together</h1>

<pre class="c">/*
 Copyright (c) 2010 The WebM project authors. All Rights Reserved.
 
 Use of this source code is governed by a BSD-style license
 that can be found in the LICENSE file in the root of the source
 tree. An additional intellectual property rights grant can be found
 in the file PATENTS. All contributing project authors may
 be found in the AUTHORS file in the root of the source tree.
 */
&nbsp;
&nbsp;
/*
 This is an example utility which drops a series of frames, as specified
 on the command line. This is useful for observing the error recovery
 features of the codec.
 */
#include &lt;stdarg.h&gt;
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;string.h&gt;
#define VPX_CODEC_DISABLE_COMPAT 1
#include &quot;./vpx_config.h&quot;
#include &quot;vpx/vp8dx.h&quot;
#include &quot;vpx/vpx_decoder.h&quot;
#define interface (vpx_codec_vp8_dx())
&nbsp;
&nbsp;
#define IVF_FILE_HDR_SZ (32)
#define IVF_FRAME_HDR_SZ (12)
&nbsp;
static unsigned int mem_get_le32&#40;const unsigned char *mem&#41; &#123;
 return &#40;mem&#91;3&#93; &lt;&lt; 24&#41;|&#40;mem&#91;2&#93; &lt;&lt; 16&#41;|&#40;mem&#91;1&#93; &lt;&lt; 8&#41;|&#40;mem&#91;0&#93;&#41;;
&#125;
&nbsp;
static void die&#40;const char *fmt, ...&#41; &#123;
 va_list ap;
&nbsp;
 va_start&#40;ap, fmt&#41;;
 vprintf&#40;fmt, ap&#41;;
 if&#40;fmt&#91;strlen&#40;fmt&#41;-1&#93; != '\n'&#41;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;\n&quot;&#41;;
 exit&#40;EXIT_FAILURE&#41;;
&#125;
&nbsp;
static void die_codec&#40;vpx_codec_ctx_t *ctx, const char *s&#41; &#123;
 const char *detail = vpx_codec_error_detail&#40;ctx&#41;;
&nbsp;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;%s: %s\n&quot;, s, vpx_codec_error&#40;ctx&#41;&#41;;
 if&#40;detail&#41;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot; %s\n&quot;,detail&#41;;
 exit&#40;EXIT_FAILURE&#41;;
&#125;
&nbsp;
&nbsp;
int main&#40;int argc, char **argv&#41; &#123;
 FILE *infile, *outfile;
 vpx_codec_ctx_t codec;
 int flags = 0, frame_cnt = 0;
 unsigned char file_hdr&#91;IVF_FILE_HDR_SZ&#93;;
 unsigned char frame_hdr&#91;IVF_FRAME_HDR_SZ&#93;;
 unsigned char frame&#91;256*1024&#93;;
 vpx_codec_err_t res;
 int n, m, is_range; //
&nbsp;
 &#40;void&#41;res;
 /* Open files */
 if&#40;argc!=4&#41; //
 die&#40;&quot;Usage: %s &lt;infile&gt; &lt;outfile&gt; &lt;N-M|N/M&gt;\n&quot;, argv&#91;0&#93;&#41;; //
 &#123; //
 char *nptr; //
 n = strtol&#40;argv&#91;3&#93;, &amp;nptr, 0&#41;; //
 m = strtol&#40;nptr+1, NULL, 0&#41;; //
 is_range = *nptr == '-'; //
 if&#40;!n || !m || &#40;*nptr != '-' &amp;&amp; *nptr != '/'&#41;&#41; //
 die&#40;&quot;Couldn't parse pattern %s\n&quot;, argv&#91;3&#93;&#41;; //
 &#125; //
 if&#40;!&#40;infile = fopen&#40;argv&#91;1&#93;, &quot;rb&quot;&#41;&#41;&#41;
 die&#40;&quot;Failed to open %s for reading&quot;, argv&#91;1&#93;&#41;;
 if&#40;!&#40;outfile = fopen&#40;argv&#91;2&#93;, &quot;wb&quot;&#41;&#41;&#41;
 die&#40;&quot;Failed to open %s for writing&quot;, argv&#91;2&#93;&#41;;
&nbsp;
 /* Read file header */
 if&#40;!&#40;fread&#40;file_hdr, 1, IVF_FILE_HDR_SZ, infile&#41; == IVF_FILE_HDR_SZ
 &amp;&amp; file_hdr&#91;0&#93;=='D' &amp;&amp; file_hdr&#91;1&#93;=='K' &amp;&amp; file_hdr&#91;2&#93;=='I'
 &amp;&amp; file_hdr&#91;3&#93;=='F'&#41;&#41;
 die&#40;&quot;%s is not an IVF file.&quot;, argv&#91;1&#93;&#41;;
&nbsp;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;Using %s\n&quot;,vpx_codec_iface_name&#40;interface&#41;&#41;;
 /* Initialize codec */
 if&#40;vpx_codec_dec_init&#40;&amp;codec, interface, NULL, flags&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to initialize decoder&quot;&#41;;
&nbsp;
 /* Read each frame */
 while&#40;fread&#40;frame_hdr, 1, IVF_FRAME_HDR_SZ, infile&#41; == IVF_FRAME_HDR_SZ&#41; &#123;
 int frame_sz = mem_get_le32&#40;frame_hdr&#41;;
 vpx_codec_iter_t iter = NULL;
 vpx_image_t *img;
&nbsp;
&nbsp;
 frame_cnt++;
 if&#40;frame_sz &gt; sizeof&#40;frame&#41;&#41;
 die&#40;&quot;Frame %d data too big for example code buffer&quot;, frame_sz&#41;;
 if&#40;fread&#40;frame, 1, frame_sz, infile&#41; != frame_sz&#41;
 die&#40;&quot;Frame %d failed to read complete frame&quot;, frame_cnt&#41;;
&nbsp;
 if&#40;&#40;is_range &amp;&amp; frame_cnt &gt;= n &amp;&amp; frame_cnt &lt;= m&#41; //
 ||&#40;!is_range &amp;&amp; m - &#40;frame_cnt-1&#41;%m &lt;= n&#41;&#41; &#123; //
 putc&#40;'X', stdout&#41;; //
 continue; //
 &#125; //
 putc&#40;'.', stdout&#41;; //
 fflush&#40;stdout&#41;; //
 /* Decode the frame */
 if&#40;vpx_codec_decode&#40;&amp;codec, frame, frame_sz, NULL, 0&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to decode frame&quot;&#41;;
&nbsp;
 /* Write decoded data to disk */
 while&#40;&#40;img = vpx_codec_get_frame&#40;&amp;codec, &amp;iter&#41;&#41;&#41; &#123;
 unsigned int plane, y;
&nbsp;
 for&#40;plane=0; plane &lt; 3; plane++&#41; &#123;
 unsigned char *buf =img-&gt;planes&#91;plane&#93;;
&nbsp;
 for&#40;y=0; y &lt; &#40;plane ? &#40;img-&gt;d_h + 1&#41; &gt;&gt; 1 : img-&gt;d_h&#41;; y++&#41; &#123;
 &#40;void&#41; fwrite&#40;buf, 1, &#40;plane ? &#40;img-&gt;d_w + 1&#41; &gt;&gt; 1 : img-&gt;d_w&#41;,
 outfile&#41;;
 buf += img-&gt;stride&#91;plane&#93;;
 &#125;
 &#125;
 &#125;
 &#125;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;Processed %d frames.\n&quot;,frame_cnt&#41;;
 if&#40;vpx_codec_destroy&#40;&amp;codec&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to destroy codec&quot;&#41;;
&nbsp;
 fclose&#40;outfile&#41;;
 fclose&#40;infile&#41;;
 return EXIT_SUCCESS;
&#125;</pre>
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