Pi4 transcoding and 'doing too much' - what has priority?

[TheRealRoland]

So far i've been using nextpvr to record without transcoding.

Just for giggles (i am filling up the second 8tb drive nicely...) i set the pvr to transcoding.

So the next time a recording finished, it would start transcoding, but also since i'm back-to-back recording, it would record the next program right after the first one stopped.

I looked at the cpu usage (btop, mainly) and saw that cpu was pegged to 100%, because, well, the transcoding mainly, but also the recording.

The next recording and going forward, i set the transcoding back to 'leave recordings in original format'.

Not that i need to transcode, but i'd like to know: what happens when there's a recording happening and the transcoding at the same place - will the recording get 'glitchy', and/or will the transcoding get glitchy because of the pi4 8gb doing too much at the same time?

[sub]

Transcoding is done at low priority, so in theory anything else happening (like a recording) will have a higher priority and will get CPU if it needs it. If nothing is happening though, then it will use the CPU until the job is complete.

[mvallevand]

The real problem is running at 100% generates lots of heat which is not good for electronics, and the RPi does start throttling the CPU which will impact the higher priority tasks too so I would expect Live TV to suffer especially with multiple recording. The RPi4 (and even 5) can really less than real time transcoding so if 2 one hour shows finish a the same time, it will be 2 hours before the transcoding is finished.

One alternative is to use the QueueProcessing function of NextTool and it can be set up to do the transcoding when the EPG update happens when there is less recording. The best solution for OTA ATSC mpeg2video is the TabloTV or HDHR extend which use h264 transcoding and you can select the bit rate at recording time.

Martin