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<p>Ahh I think its</p>
<pre class="lang-cpp prettyprint prettyprinted" style=""><code><span class="typ">AVInputFormat</span><span class="pln"> </span><span class="pun">*</span><span class="pln">inputFormat </span><span class="pun">=</span><span class="pln">av_find_input_format</span><span class="pun">(</span><span class="str">"</span></code><code><span class="str">libvpx"</span><span class="pun">);
</span></code><code><span class="pun"></span><span class="pln">avformat_open_input</span><span class="pun">(&</span><span class="pln">pAVFormatContext</span><span class="pun">,</span><span class="pln"> dev_name</span><span class="pun">,</span><span class="pln"> inputFormat</span><span class="pun">,</span><span class="pln"> NULL</span><span class="pun">)</span><span class="pln"> </span></code>
<code><span class="pun"></span></code></pre>
<br>
<div class="moz-cite-prefix">On 6/15/2018 11:49 AM, Mark Schafer
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:d55d093e-4a69-3ab5-4e52-62375b822cd0@wireframe.biz">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="moz-txt-link-rfc2396E" href="mailto:mschafer@wireframe.biz"><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="moz-txt-link-freetext" href="https://simpl.info/videoalpha/">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_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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</blockquote>
<br>
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