Decode 4k h265 videos

[malhosary]

Thanks for the great work, it actually works very well with h264 and h265 video files up to HD resolution.
Decoding h264 4k video files works at about 10 fps and Decoding h265 4k video files works at about 3 fps.
I did some logs in the video_decoder.c file to check out what is going on. FFMPEG method: av_send_packet actually takes the longest execution time (about 350 ms per frame for h265 4k files), other methods are working very well.

Any ideas how to improve the performance of this method? I knew that this might be a limitation from web assembly technology itself, but can we somehow enable multi-threading or hardware acceleration to get better performance?