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<div dir="ltr">> Still investigating the problem, by constraining my application with -qmin=10 -qmax=10, and doing the same using ffmpeg command line I have the exact same bitrate and file size.</div>
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<div dir="ltr">I had similar problems and I found that the problem was my video stream time_base.<br>
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<div dir="ltr">When you call avformat_write_header() avformat silently change your stream time_base to some values that it likes, so you cannot assume that the video stream time_base was the one you have configured on the stream creation but you need to do
before encoding every frame:<br>
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<span><span style="color: rgb(220, 220, 170);">av_packet_rescale_ts</span><span>(</span><span style="color: rgb(156, 220, 254);">pkt_</span><span>,
</span><span style="color: rgb(156, 220, 254);">vc_</span><span>-></span><span style="color: rgb(156, 220, 254);">time_base</span><span>,
</span><span style="color: rgb(156, 220, 254);">vs_</span><span>-></span><span style="color: rgb(156, 220, 254);">time_base</span><span>);</span></span><br>
<span><span></span><span style="color: rgb(220, 220, 170);">av_interleaved_write_frame</span><span>(</span><span style="color: rgb(156, 220, 254);">oc_</span><span>,
</span><span style="color: rgb(156, 220, 254);">pkt_</span><span>);</span></span></div>
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<div dir="ltr">if you don't do that x264 (and other encoders) will think that the frame duration is different from the real one and will behave accordingly.<br>
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The problem was more evident when encoding with videotoolbox on macOS that has a fixed bitrate mode.<br>
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