<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=us-ascii">
<meta name="Generator" content="Microsoft Word 14 (filtered medium)">
<style><!--
/* Font Definitions */
@font-face
{font-family:"Cambria Math";
panose-1:2 4 5 3 5 4 6 3 2 4;}
@font-face
{font-family:Calibri;
panose-1:2 15 5 2 2 2 4 3 2 4;}
@font-face
{font-family:Consolas;
panose-1:2 11 6 9 2 2 4 3 2 4;}
/* Style Definitions */
p.MsoNormal, li.MsoNormal, div.MsoNormal
{margin:0cm;
margin-bottom:.0001pt;
font-size:11.0pt;
font-family:"Calibri","sans-serif";}
a:link, span.MsoHyperlink
{mso-style-priority:99;
color:blue;
text-decoration:underline;}
a:visited, span.MsoHyperlinkFollowed
{mso-style-priority:99;
color:purple;
text-decoration:underline;}
span.EmailStyle17
{mso-style-type:personal-compose;
font-family:"Calibri","sans-serif";
color:windowtext;}
.MsoChpDefault
{mso-style-type:export-only;
font-family:"Calibri","sans-serif";}
@page WordSection1
{size:612.0pt 792.0pt;
margin:72.0pt 72.0pt 72.0pt 72.0pt;}
div.WordSection1
{page:WordSection1;}
--></style><!--[if gte mso 9]><xml>
<o:shapedefaults v:ext="edit" spidmax="1026" />
</xml><![endif]--><!--[if gte mso 9]><xml>
<o:shapelayout v:ext="edit">
<o:idmap v:ext="edit" data="1" />
</o:shapelayout></xml><![endif]-->
</head>
<body lang="EN-US" link="blue" vlink="purple">
<div class="WordSection1">
<p class="MsoNormal">I am trying to write an .mp4 video with a specified bitrate and gopsize set to 1.<o:p></o:p></p>
<p class="MsoNormal">Apparently libavcodec ignores the settings I provide and creates a video with a much higher bitrate<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Here’s the code I use to setup the output video:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:black"> m_pcVideoSt->codec->gop_size = m_iGopSize;
</span><span style="font-size:9.5pt;font-family:Consolas;color:green">/* emit one intra frame every m_iGopSize frames at most */</span><span style="font-size:9.5pt;font-family:Consolas;color:black"><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:black"> m_pcVideoSt->codec->pix_fmt = AV_PIX_FMT_YUV420P;
</span><span style="font-size:9.5pt;font-family:Consolas;color:green">/* default pix_fmt */</span><span style="font-size:9.5pt;font-family:Consolas;color:black"><o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.5pt;font-family:Consolas;color:black"> m_pcVideoSt->codec->max_b_frames = 1;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:black"> AVDictionary* pcOpts =
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">nullptr</span><span style="font-size:9.5pt;font-family:Consolas;color:black">;<o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:9.5pt;font-family:Consolas;color:black">
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">int</span><span style="font-size:9.5pt;font-family:Consolas;color:black"> res1 = av_dict_set(&pcOpts,
</span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515">"b"</span><span style="font-size:9.5pt;font-family:Consolas;color:black">,
</span><span style="font-size:9.5pt;font-family:Consolas;color:#A31515">"20k"</span><span style="font-size:9.5pt;font-family:Consolas;color:black">, 0);<o:p></o:p></span></p>
<p class="MsoNormal"><span style="font-size:9.5pt;font-family:Consolas;color:black">
</span><span style="font-size:9.5pt;font-family:Consolas;color:blue">int</span><span style="font-size:9.5pt;font-family:Consolas;color:black"> res = avcodec_open2(m_pcVideoSt->codec, codec, &pcOpts);</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">m_pcVideoSt is of type <span style="font-size:9.5pt;font-family:Consolas;color:black">
AVStream*</span><o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">This is the output of ffprobe ran on the video I wrote:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New"">Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'testGray.mp4':</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> Metadata:</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> major_brand : isom</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> minor_version : 512</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> compatible_brands: isomiso2avc1mp41</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> encoder : Lavf56.40.101</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> Duration: 00:00:20.00, start: 0.000000, bitrate: 8905 kb/s</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 720x576, 8904 kb/s, 25 fps, 25 tbr, 12800 tbn, 50 tbc (default)</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> Metadata:</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal" style="text-autospace:none"><span style="font-size:10.0pt;font-family:"Courier New""> handler_name : VideoHandler</span><span style="font-size:12.0pt;font-family:"Courier New""><o:p></o:p></span></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">When watching the video, it seems that the quality is low for the first few frames, but then the quality gets much better (explaining the 8905Kb/s bitrate).<o:p></o:p></p>
<p class="MsoNormal">Any idea on what I am missing?<o:p></o:p></p>
</div>
</body>
</html>