2019-04-23, 09:38
As the title suggests, playing back high bitrate 2160p60 (like the 75mbps Sony Camp Demo) content exhibits constant stuttering when being played via network (DLNA and SMB).
Playback device is a Sony BRAVIA KD-65XF9005 with quad core ARM Cortex [email protected], running Android TV Oreo and Kodi v19 nightly (20190421-910276e130). Network connection has been established via fast 802.11ac WiFi.
Lower bitrate 2160p60 content (like The World in HDR @ 15mbps) exhibits less stuttering. Also playback via USB is mostly fine. So one might assume a network bandwidth issue…
Here is why I can rule out a network bandwidth problem
Some additional findings
What I observed during playback of high bitrate content was that SIRQ and CPU load in general used to be very high, much higher than with VLC for example. Stuttering typically occurred during CPU load peaks. Lower bitrate clips suffered less from such peaks (The World in HDR), as did playback via USB, hence the smoother playback.
Playback over DLNA suffers from more frequent stuttering compared to SMB. Overall CPU usage is lower with SMB, also exhibiting less peaks, which most probably is the reason why. VLC works without stuttering over DLNA. CPU usage again is quite a bit lower.
Kodi does not register those jerks as frame drops/skips. So it might happen at a later stage in the pipeline (SurfaceFlinger?). I am not sure whether a log or systrace would help pinpointing the issue as it most probably has quite an impact on timings too.
Possible optimizations
Playback device is a Sony BRAVIA KD-65XF9005 with quad core ARM Cortex [email protected], running Android TV Oreo and Kodi v19 nightly (20190421-910276e130). Network connection has been established via fast 802.11ac WiFi.
Lower bitrate 2160p60 content (like The World in HDR @ 15mbps) exhibits less stuttering. Also playback via USB is mostly fine. So one might assume a network bandwidth issue…
Here is why I can rule out a network bandwidth problem
- VLC plays high bitrate 2160p60 just fine (at a much lower CPU usage).
- iperf3 attests a sustained throughput of 250mbps.
- Jellyfish files play fine up to 160mbps. Those are 30fps however, so being much more lenient with respect to frame timings.
- Kodi player controls suggest that buffers are sufficiently filled (I also pause playback in the beginning in order to fill up buffers). Playing around with cache settings did not yield any improvements.
Some additional findings
What I observed during playback of high bitrate content was that SIRQ and CPU load in general used to be very high, much higher than with VLC for example. Stuttering typically occurred during CPU load peaks. Lower bitrate clips suffered less from such peaks (The World in HDR), as did playback via USB, hence the smoother playback.
Playback over DLNA suffers from more frequent stuttering compared to SMB. Overall CPU usage is lower with SMB, also exhibiting less peaks, which most probably is the reason why. VLC works without stuttering over DLNA. CPU usage again is quite a bit lower.
Kodi does not register those jerks as frame drops/skips. So it might happen at a later stage in the pipeline (SurfaceFlinger?). I am not sure whether a log or systrace would help pinpointing the issue as it most probably has quite an impact on timings too.
Possible optimizations
- Increase READ_CACHE_CHUNK_SIZE in order to reduce SIRQ load
- Amazon elaborates on timing issues when having to render a 4K frame every 16ms (60p). They suggest Tunnel Mode Playback. Kodi would probably also benefit from processing data via MediaCodec asynchronously (NDK only supports this as of Pie/API Level 28).
