no timestamps are being input in the encoder, thus don't output any

this fixes muxing to libvorbis, and possibly others

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
Signed-off-by: Benjamin Drung <bdrung@debian.org>

src/export/ExportFFmpeg.cpp

@@ -578,6 +578,7 @@ static int encode_audio(AVCodecContext *avctx, AVPacket *pkt, int nFifoBytes, in
       return ret;
    }
 
+   pkt->dts = pkt->pts = AV_NOPTS_VALUE; // we dont set frame.pts thus dont trust the AVPacket ts
 
    av_frame_free(&frame);
    av_freep(&samples);