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<h1>VP8 Set Reference Frame</h1>

This is an example demonstrating how to overwrite the VP8 encoder&#8217;s
internal reference frame. In the sample we set the last frame to the
current frame. If this is done at a cut scene it will avoid a keyframe.
This technique could be used to bounce between two cameras.

Note that the decoder would also have to set the reference frame to the
same value on the same frame, or the video will become corrupt.

<h2>Usage</h2>

This example adds a single argument to the <code>simple_encoder</code> example,
which specifies the frame number to update the reference frame on.
The parameter is parsed as follows:

<pre class="c">if&#40;argc!=6&#41;
 die&#40;&quot;Usage: %s &lt;width&gt; &lt;height&gt; &lt;infile&gt; &lt;outfile&gt; &lt;frame&gt;\n&quot;,
 argv&#91;0&#93;&#41;;
&nbsp;
 update_frame_num = atoi&#40;argv&#91;5&#93;&#41;;
 if&#40;!update_frame_num&#41;
 die&#40;&quot;Couldn't parse frame number '%s'\n&quot;, argv&#91;5&#93;&#41;;
&nbsp;</pre>

<h2>Extra Variables</h2>

This example maintains the frame number passed on the command line
in the <code>update_frame_num</code> variable:

<pre class="c">int update_frame_num = 0;</pre>

<h2>Configuration</h2>

The reference frame is updated on the frame specified on the command
line.

<pre class="c">frame_avail = read_frame&#40;infile, &amp;raw&#41;;
&nbsp;
if&#40;frame_cnt + 1 == update_frame_num&#41; &#123;
 vpx_ref_frame_t ref;
&nbsp;
 ref.frame_type = VP8_LAST_FRAME;
 ref.img = raw;
&nbsp;
 if&#40;vpx_codec_control&#40;&amp;codec, VP8_SET_REFERENCE, &amp;ref&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to set reference frame&quot;&#41;;
&#125;
&nbsp;
if&#40;vpx_codec_encode&#40;&amp;codec, frame_avail? &amp;raw : NULL, frame_cnt,
 1, flags, VPX_DL_REALTIME&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to encode frame&quot;&#41;;</pre>

<h2>Observing The Effects</h2>

Use the <code>simple_encoder</code> example to encode a sample with a cut scene.
Determine the frame number of the cut scene by looking for a generated
key-frame (indicated by a &#8216;K&#8217;). Supply that frame number as an argument
to this example, and observe that no key-frame is generated.

<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 demonstrating how to overwrite the VP8 encoder's
 internal reference frame. In the sample we set the last frame to the
 current frame. If this is done at a cut scene it will avoid a keyframe.
 This technique could be used to bounce between two cameras.
 
 Note that the decoder would also have to set the reference frame to the
 same value on the same frame, or the video will become corrupt.
 */
#include &lt;stdio.h&gt;
#include &lt;stdlib.h&gt;
#include &lt;stdarg.h&gt;
#include &lt;string.h&gt;
#define VPX_CODEC_DISABLE_COMPAT 1
#include &quot;vpx/vpx_encoder.h&quot;
#include &quot;vpx/vp8cx.h&quot;
#define interface (vpx_codec_vp8_cx())
#define fourcc 0x30385056
&nbsp;
#define IVF_FILE_HDR_SZ (32)
#define IVF_FRAME_HDR_SZ (12)
&nbsp;
static void mem_put_le16&#40;char *mem, unsigned int val&#41; &#123;
 mem&#91;0&#93; = val;
 mem&#91;1&#93; = val&gt;&gt;8;
&#125;
&nbsp;
static void mem_put_le32&#40;char *mem, unsigned int val&#41; &#123;
 mem&#91;0&#93; = val;
 mem&#91;1&#93; = val&gt;&gt;8;
 mem&#91;2&#93; = val&gt;&gt;16;
 mem&#91;3&#93; = val&gt;&gt;24;
&#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;
static int read_frame&#40;FILE *f, vpx_image_t *img&#41; &#123;
 size_t nbytes, to_read;
 int res = 1;
&nbsp;
 to_read = img-&gt;w*img-&gt;h*3/2;
 nbytes = fread&#40;img-&gt;planes&#91;0&#93;, 1, to_read, f&#41;;
 if&#40;nbytes != to_read&#41; &#123;
 res = 0;
 if&#40;nbytes &gt; 0&#41;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;Warning: Read partial frame. Check your width &amp; height!\n&quot;&#41;;
 &#125;
 return res;
&#125;
&nbsp;
static void write_ivf_file_header&#40;FILE *outfile,
 const vpx_codec_enc_cfg_t *cfg,
 int frame_cnt&#41; &#123;
 char header&#91;32&#93;;
&nbsp;
 if&#40;cfg-&gt;g_pass != VPX_RC_ONE_PASS &amp;&amp; cfg-&gt;g_pass != VPX_RC_LAST_PASS&#41;
 return;
 header&#91;0&#93; = 'D';
 header&#91;1&#93; = 'K';
 header&#91;2&#93; = 'I';
 header&#91;3&#93; = 'F';
 mem_put_le16&#40;header+4, 0&#41;; /* version */
 mem_put_le16&#40;header+6, 32&#41;; /* headersize */
 mem_put_le32&#40;header+8, fourcc&#41;; /* headersize */
 mem_put_le16&#40;header+12, cfg-&gt;g_w&#41;; /* width */
 mem_put_le16&#40;header+14, cfg-&gt;g_h&#41;; /* height */
 mem_put_le32&#40;header+16, cfg-&gt;g_timebase.den&#41;; /* rate */
 mem_put_le32&#40;header+20, cfg-&gt;g_timebase.num&#41;; /* scale */
 mem_put_le32&#40;header+24, frame_cnt&#41;; /* length */
 mem_put_le32&#40;header+28, 0&#41;; /* unused */
&nbsp;
 &#40;void&#41; fwrite&#40;header, 1, 32, outfile&#41;;
&#125;
&nbsp;
&nbsp;
static void write_ivf_frame_header&#40;FILE *outfile,
 const vpx_codec_cx_pkt_t *pkt&#41;
&#123;
 char header&#91;12&#93;;
 vpx_codec_pts_t pts;
&nbsp;
 if&#40;pkt-&gt;kind != VPX_CODEC_CX_FRAME_PKT&#41;
 return;
&nbsp;
 pts = pkt-&gt;data.frame.pts;
 mem_put_le32&#40;header, pkt-&gt;data.frame.sz&#41;;
 mem_put_le32&#40;header+4, pts&amp;0xFFFFFFFF&#41;;
 mem_put_le32&#40;header+8, pts &gt;&gt; 32&#41;;
&nbsp;
 &#40;void&#41; fwrite&#40;header, 1, 12, outfile&#41;;
&#125;
&nbsp;
int main&#40;int argc, char **argv&#41; &#123;
 FILE *infile, *outfile;
 vpx_codec_ctx_t codec;
 vpx_codec_enc_cfg_t cfg;
 int frame_cnt = 0;
 vpx_image_t raw;
 vpx_codec_err_t res;
 long width;
 long height;
 int frame_avail;
 int got_data;
 int flags = 0;
 int update_frame_num = 0; //
&nbsp;
 /* Open files */
 if&#40;argc!=6&#41; //
 die&#40;&quot;Usage: %s &lt;width&gt; &lt;height&gt; &lt;infile&gt; &lt;outfile&gt; &lt;frame&gt;\n&quot;, //
 argv&#91;0&#93;&#41;; //
 //
 update_frame_num = atoi&#40;argv&#91;5&#93;&#41;; //
 if&#40;!update_frame_num&#41; //
 die&#40;&quot;Couldn't parse frame number '%s'\n&quot;, argv&#91;5&#93;&#41;; //
 //
 width = strtol&#40;argv&#91;1&#93;, NULL, 0&#41;;
 height = strtol&#40;argv&#91;2&#93;, NULL, 0&#41;;
 if&#40;width &lt; 16 || width%2 || height &lt;16 || height%2&#41;
 die&#40;&quot;Invalid resolution: %ldx%ld&quot;, width, height&#41;;
 if&#40;!vpx_img_alloc&#40;&amp;raw, VPX_IMG_FMT_I420, width, height, 1&#41;&#41;
 die&#40;&quot;Faile to allocate image&quot;, width, height&#41;;
 if&#40;!&#40;outfile = fopen&#40;argv&#91;4&#93;, &quot;wb&quot;&#41;&#41;&#41;
 die&#40;&quot;Failed to open %s for writing&quot;, argv&#91;4&#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;;
&nbsp;
 /* Populate encoder configuration */
 res = vpx_codec_enc_config_default&#40;interface, &amp;cfg, 0&#41;;
 if&#40;res&#41; &#123;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;Failed to get config: %s\n&quot;, vpx_codec_err_to_string&#40;res&#41;&#41;;
 return EXIT_FAILURE;
 &#125;
&nbsp;
 /* Update the default configuration with our settings */
 cfg.rc_target_bitrate = width * height * cfg.rc_target_bitrate
 / cfg.g_w / cfg.g_h;
 cfg.g_w = width;
 cfg.g_h = height;
&nbsp;
 write_ivf_file_header&#40;outfile, &amp;cfg, 0&#41;;
&nbsp;
&nbsp;
 /* Open input file for this encoding pass */
 if&#40;!&#40;infile = fopen&#40;argv&#91;3&#93;, &quot;rb&quot;&#41;&#41;&#41;
 die&#40;&quot;Failed to open %s for reading&quot;, argv&#91;3&#93;&#41;;
&nbsp;
 /* Initialize codec */
 if&#40;vpx_codec_enc_init&#40;&amp;codec, interface, &amp;cfg, 0&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to initialize encoder&quot;&#41;;
&nbsp;
 frame_avail = 1;
 got_data = 0;
 while&#40;frame_avail || got_data&#41; &#123;
 vpx_codec_iter_t iter = NULL;
 const vpx_codec_cx_pkt_t *pkt;
&nbsp;
 frame_avail = read_frame&#40;infile, &amp;raw&#41;; //
 //
 if&#40;frame_cnt + 1 == update_frame_num&#41; &#123; //
 vpx_ref_frame_t ref; //
 //
 ref.frame_type = VP8_LAST_FRAME; //
 ref.img = raw; //
 //
 if&#40;vpx_codec_control&#40;&amp;codec, VP8_SET_REFERENCE, &amp;ref&#41;&#41; //
 die_codec&#40;&amp;codec, &quot;Failed to set reference frame&quot;&#41;; //
 &#125; //
 //
 if&#40;vpx_codec_encode&#40;&amp;codec, frame_avail? &amp;raw : NULL, frame_cnt, //
 1, flags, VPX_DL_REALTIME&#41;&#41; //
 die_codec&#40;&amp;codec, &quot;Failed to encode frame&quot;&#41;; //
 got_data = 0;
 while&#40; &#40;pkt = vpx_codec_get_cx_data&#40;&amp;codec, &amp;iter&#41;&#41; &#41; &#123;
 got_data = 1;
 switch&#40;pkt-&gt;kind&#41; &#123;
 case VPX_CODEC_CX_FRAME_PKT:
 write_ivf_frame_header&#40;outfile, pkt&#41;;
 &#40;void&#41; fwrite&#40;pkt-&gt;data.frame.buf, 1, pkt-&gt;data.frame.sz,
 outfile&#41;;
 break;
 default:
 break;
 &#125;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;pkt-&gt;kind == VPX_CODEC_CX_FRAME_PKT
 &amp;&amp; &#40;pkt-&gt;data.frame.flags &amp; VPX_FRAME_IS_KEY&#41;? &quot;K&quot;:&quot;.&quot;&#41;;
 fflush&#40;stdout&#41;;
 &#125;
 frame_cnt++;
 &#125;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;\n&quot;&#41;;
 fclose&#40;infile&#41;;
&nbsp;
 <a href="http://www.opengroup.org/onlinepubs/009695399/functions/printf.html">printf</a>&#40;&quot;Processed %d frames.\n&quot;,frame_cnt-1&#41;;
 vpx_img_free&#40;&amp;raw&#41;;
 if&#40;vpx_codec_destroy&#40;&amp;codec&#41;&#41;
 die_codec&#40;&amp;codec, &quot;Failed to destroy codec&quot;&#41;;
&nbsp;
 /* Try to rewrite the file header with the actual frame count */
 if&#40;!fseek&#40;outfile, 0, SEEK_SET&#41;&#41;
 write_ivf_file_header&#40;outfile, &amp;cfg, frame_cnt-1&#41;;
 fclose&#40;outfile&#41;;
 return EXIT_SUCCESS;
&#125;</pre>
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