Web-ui transcoder speed with different channels

Channels DVR Server
#1

I record OTA channels using a pair of Extend HDHomeRun devices. All recordings are stored as H.264 as sent from the HDHR.

When playing back recordings via the web-ui, all shows from the following channels work great and have high transcode rates at any resolution/bitrate: ABC, Fox, The CW, MyTV

However, all shows from some other channels don’t always stay above 1x transcode, even when adjusting transcode settings: CBS, NBC, PBS, Create

All of the shows are recording using the same devices and stored on the same synology server. What is different about the stored video from some channels that makes the transcode so much slower?

1 Like
#2

What stands in your post, for me, are the channel groupings.

CBS, NBC and PBS broadcast in 1080i.

ABC and FOX broadcast in 720P. I’m guessing the CW and MyTV channels are in 720P also.

#3

If deinterlacing is a bottleneck, you can try switching to Blend instead of Linear.

#4

ok, so the channels that are slower to transcode require an extra deinterlacing step. I can make it work by lowering the transcode settings. In this case, maybe it would be useful for the web-ui to have two different transcode settings. One for channels that are already progressive scan and one for channels that require deinterlacing.

#5

So, at the moment if your recording is already in H264 and it is progressive, no transcoding takes place. The video is remuxed and served up at the original bitrate/resolution. When the recording is interlaced, it is fully transcoded which means it has to be decoded, deinterlaced and then encoded. The encoding can use hardware, but the first two steps do not.

There are plans to move both decoding and deinterlacing into hardware, as well as allowing progressive recordings to be re-encoded at a lower bitrate for remote viewing.

#6

I am unaware of all of the technicalities of processing different OTA channels. It must be the remux that is slowing it down, then. All I know is that the recordings from one group of channels transcode via web-ui at over 8x faster than recordings from another group of different channels. So I need to change the transcoder setting, depending on what channel the show was recorded from.

#7

My point was that on the channels that you see 8x speeds, no transcoding is taking place. So for those channels, the setting does not matter. The setting is only used for the channels with interlacing. So you don’t need two different settings, because the setting already only applies to the channels which are slower.

#8

Ok, I get it now. Thanks for the explanation. Does interlaced video need to be deinterlaced at all? I hope the eventual hardware decode/deinterlacing speeds this up a bit.

#9

Yes it has to be deinterlaced, or it will look terrible. If you use the ATV for playback, the deinterlacing happens on the ATV and is quite fast. Same will be true of iOS when DVR features are added there.