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<p>Brilliant thanks Anton.</p>
<p>Just to be complete if its codec "139 - Google VP8" then you need
to find "libvpx-vp8" and<br>
if its "167 - Google VP9" then you need to find "libvpx-vp9".</p>
<p>Also you can load a stream with avcodec_open2 and override the
codec there instead.<br>
</p>
<br>
<div class="moz-cite-prefix">On 6/15/2018 7:25 PM, Anton Shekhovtsov
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CAMdg9b2tK+iTdJ3r0KGonLUe8pdKnN7YFqjXzWdpRQGcOrUnOw@mail.gmail.com">
<div dir="ltr">Hi, "libvpx" is not input format, see this for
example
<div><br>
</div>
<div>
<div> AVCodec* pDecoder =
avcodec_find_decoder(m_pStreamCtx->codecpar->codec_id);</div>
<div>
if(m_pStreamCtx->codecpar->codec_id==AV_CODEC_ID_VP8){</div>
<div> // on2 vp8 does not extract alpha</div>
<div> AVCodec* pDecoder2 =
avcodec_find_decoder_by_name("libvpx");</div>
<div> if(pDecoder2) pDecoder = pDecoder2;</div>
<div> }</div>
</div>
<div><br>
</div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2018-06-15 3:02 GMT+03:00 Mark Schafer
<span dir="ltr"><<a href="mailto:mschafer@wireframe.biz"
target="_blank" moz-do-not-send="true">mschafer@wireframe.biz</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">
<div text="#000000" bgcolor="#FFFFFF">
<p>Ahh I think its</p>
<pre class="m_589738237636612550lang-cpp m_589738237636612550prettyprint m_589738237636612550prettyprinted"><code><span class="m_589738237636612550typ">AVInputFormat</span><span class="m_589738237636612550pln"> </span><span class="m_589738237636612550pun">*</span><span class="m_589738237636612550pln">inputFormat </span><span class="m_589738237636612550pun">=</span><span class="m_589738237636612550pln">av_find_input_format</span><span class="m_589738237636612550pun">(</span><span class="m_589738237636612550str">"</span></code><code><span class="m_589738237636612550str">libvpx"</span><span class="m_589738237636612550pun"><wbr>);
</span></code><code><span class="m_589738237636612550pun"></span><span class="m_589738237636612550pln">avformat_open_input</span><span class="m_589738237636612550pun">(&</span><span class="m_589738237636612550pln">pAVFormat<wbr>Context</span><span class="m_589738237636612550pun">,</span><span class="m_589738237636612550pln"> dev_name</span><span class="m_589738237636612550pun">,</span><span class="m_589738237636612550pln"> inputFormat</span><span class="m_589738237636612550pun">,</span><span class="m_589738237636612550pln"> NULL</span><span class="m_589738237636612550pun">)</span><span class="m_589738237636612550pln"> </span></code>
<code><span class="m_589738237636612550pun"></span></code></pre>
<div>
<div class="h5"> <br>
<div class="m_589738237636612550moz-cite-prefix">On
6/15/2018 11:49 AM, Mark Schafer wrote:<br>
</div>
<blockquote type="cite">OK. Thanks Carl. <br>
<br>
So you're saying I should always override it with
libvpx if the file I'm loading is .webm ? <br>
and if you don't mind - how do I override the codec
on load ? <br>
Is it in AVInputFormat by stipulating the extension
and codec_tag ? <br>
<br>
<br>
On 6/15/2018 11:13 AM, Carl Eugen Hoyos wrote: <br>
<blockquote type="cite">2018-06-14 23:03 GMT+02:00,
Mark Schafer <a
class="m_589738237636612550moz-txt-link-rfc2396E"
href="mailto:mschafer@wireframe.biz"
target="_blank" moz-do-not-send="true"><mschafer@wireframe.biz></a>:
<br>
<blockquote type="cite">We're trying to integrate
ffmpeg 4 with Pyglet. <br>
Its all going very well but we have one issue: <br>
<br>
- If a VP9 (or VP8) file is created using
ffmpeg4 from png files with <br>
alphas, we get a video file (webm) with alpha
internally. (Excellent) <br>
- ffmpeg -i image_seq%03d.png -qmin 0 -qmax 50
-crf 5 -b:v 1M output.webm <br>
- The report from this CLI indicates that
an alpha has been generated. <br>
<br>
- Sample webm videos with alpha can be found on
this page: <br>
<a
class="m_589738237636612550moz-txt-link-freetext"
href="https://simpl.info/videoalpha/"
target="_blank" moz-do-not-send="true">https://simpl.info/videoalpha/</a>
<br>
- However on playing back we only get the RGB
and do not get the alpha <br>
unless we override the codec to be 'libvpx'. <br>
</blockquote>
Yes, this is a known limitation of the native
decoder, luckily you <br>
have already found the only known work-around -
not to use it if <br>
you need this feature. <br>
<br>
If you really want to choose the decoder based on
the alpha <br>
layer, you can check AV_PKT_DATA_MATROSKA_<wbr>BLOCKADDITIONAL
<br>
if the side_data starts with (uint64_t) 1 there is
a transparency layer. <br>
<br>
It is probably simpler to always use the libvpx
decoder. <br>
<br>
Carl Eugen <br>
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