Massive MP4 conversion speed improvement

[obilodeau]

Did some profiling with snakeviz today. It was clear where the bulk of our time was spent:

Reading about ImageQt.fromqimage() I found out that it would compress to png the whole frame. That operation is completely unnecessary here since PyAV will perform compression to video as well. I found a way to pass an array of bytes instead using numpy. Here are the benchmarks.

with from_image via QTImage:

$ time pyrdp-convert.py pyrdp_output/replays/rdp_replay_20210826_12-15-33_512_Stephen215343.pyrdp -f mp4
[*] Converting 'pyrdp_output/replays/rdp_replay_20210826_12-15-33_512_Stephen215343.pyrdp' to MP4
100% (1465 of 1465) |##################################################################################| Elapsed Time: 0:07:08 Time:  0:07:08

[+] Succesfully wrote 'rdp_replay_20210826_12-15-33_512_Stephen215343.mp4'

real	7m23.110s
user	7m33.381s
sys	0m8.217s

with from_ndarray and qimage2ndarray:

$ time pyrdp-convert.py pyrdp_output/replays/rdp_replay_20210826_12-15-33_512_Stephen215343.pyrdp -f mp4
[*] Converting 'pyrdp_output/replays/rdp_replay_20210826_12-15-33_512_Stephen215343.pyrdp' to MP4
100% (1465 of 1465) |##################################################################################| Elapsed Time: 0:00:55 Time:  0:00:55

[+] Succesfully wrote 'rdp_replay_20210826_12-15-33_512_Stephen215343.mp4'

real	0m59.565s
user	1m20.037s
sys	0m1.196s

This will probably have an impact of our full image size since numpy will be pulled in. However, I think I can get rid of PIL. I'll let CI decide.

I compared the resulting MP4 visually and didn't find a noticeable difference.