2016-05-01, 22:40
OK - been pushing the boundaries on the C2 this weekend. For no real reason other than... well... because...
I have quite a lot of very high quality 1080/50i H264 4:2:2 recordings which are encoded at around 38Mbs. The only things that play them are Intel x86 boxes with enough ponies for CPU decode and deinterlace. They won't play on a Pi 1/2/3 or an ODroid - as they are only geared up for 4:2:0 consumer stuff.
So I decided to push things a bit and also see how the C2 coped with challenging content. So I've run my 38Mbs 1080/50i H264 4:2:2 stuff through ffmpeg encoding it to H265 and deinterlacing to 1080/50p prior to encoding (I've had some issues with 1080i 4:2:2 to 1080i 4:2:0 with ffmpeg in the past with odd chroma resampling artefacts interacting with interlaced motion, and I also wanted to trial YADIF vs W3FDIF)
So I encoded a 4 hour show to 1080/50p H265 4:2:0 at an average bitrate of 35Mbs. However the show varied between very challenging and very unchallenging content. And the challenging content peaked at over 80Mbs.
And on a couple of occasions the C2 has choked on H265 at this bitrate and visually started dropping frames (though the Kodi OSD doesn't reflect this). I'm playing it from a pretty fast SSD over a USB 2 connection but 80Mbs is only 10MBs so it should't be close to the limits of SSD. They are very rare - and only correlated with insanely high bitrates. When I next have a free 30 hours I'll render the same content out with a capped maximum bitrate...
** EDIT - have transferred test files at bitrates from 1Mbs to 50Mbs with the same content to the eMMC. The C2 HEVC decoder implementation in current Kodi chokes on spikes of bitrate that peak at high levels. These won't be hit in 'real world' content - but it's been an interesting stress test. And I can confirm that the ffmpeg single pass x265 encoder doesn't really do amazingly well at 1Mbs with 1080/50p **
I'm still amazed that a box like the C2 can do this though - it's playing a bleeding edge codec at high bitrates and is a very low cost device...
I have quite a lot of very high quality 1080/50i H264 4:2:2 recordings which are encoded at around 38Mbs. The only things that play them are Intel x86 boxes with enough ponies for CPU decode and deinterlace. They won't play on a Pi 1/2/3 or an ODroid - as they are only geared up for 4:2:0 consumer stuff.
So I decided to push things a bit and also see how the C2 coped with challenging content. So I've run my 38Mbs 1080/50i H264 4:2:2 stuff through ffmpeg encoding it to H265 and deinterlacing to 1080/50p prior to encoding (I've had some issues with 1080i 4:2:2 to 1080i 4:2:0 with ffmpeg in the past with odd chroma resampling artefacts interacting with interlaced motion, and I also wanted to trial YADIF vs W3FDIF)
So I encoded a 4 hour show to 1080/50p H265 4:2:0 at an average bitrate of 35Mbs. However the show varied between very challenging and very unchallenging content. And the challenging content peaked at over 80Mbs.
And on a couple of occasions the C2 has choked on H265 at this bitrate and visually started dropping frames (though the Kodi OSD doesn't reflect this). I'm playing it from a pretty fast SSD over a USB 2 connection but 80Mbs is only 10MBs so it should't be close to the limits of SSD. They are very rare - and only correlated with insanely high bitrates. When I next have a free 30 hours I'll render the same content out with a capped maximum bitrate...
** EDIT - have transferred test files at bitrates from 1Mbs to 50Mbs with the same content to the eMMC. The C2 HEVC decoder implementation in current Kodi chokes on spikes of bitrate that peak at high levels. These won't be hit in 'real world' content - but it's been an interesting stress test. And I can confirm that the ffmpeg single pass x265 encoder doesn't really do amazingly well at 1Mbs with 1080/50p **
I'm still amazed that a box like the C2 can do this though - it's playing a bleeding edge codec at high bitrates and is a very low cost device...
