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Thread: Why is transcoding required for Live TV.

  1. #1
    Join Date
    Jan 2006

    Why is transcoding required for Live TV.

    I'm running NextPVR on a dedicated fairly low end nettop box (Acer AspireRevo AR1600) under Windows XP. Works great. I have 2 HD-PVRs and do Live TV through Kodi on Android tablets and Fire TV devices. I recently purchased the iOS application and once I had installed an XP compatible version of ffmpeg can get Live TV to start but not run. By start I mean an HD-PVR fires up, the CPU on the server gets pegged at 100%, the HD-PVR stops (the log says - Live stream expired without 15 second renewal.) and eventually the short TV clip plays on my iPhone.

    Pretty sure it is the transcoding that's killing me here. Hence my question as to why it's necessary? Streaming live TV to Kodi on the Android boxes works great without transcoding. The HD-PVR produces an h.264 stream right?


  2. #2
    Join Date
    Nov 2003
    NextPVR HQ, Wellington, New Zealand
    The vast majority of people need their TV signals to be transcoded to get it to H.264/AAC for playback on an iOS device, and it's much cleaner and more straight forward for the application to feed all the video streams through the same processing logic, so by default everything is transcoded for this delivery.

    As you mentioned though, video from an HD-PVR is H.264 so in theory it could be delivered as-is, but a very small portion of the community is in this position, so it wasn't worth complicating the design to accommodate this scenario. Also, things are never that straight forward - I've seen native H.264 streams that just don't play on iOS devices (due to H.264 profile and level), so often need transcoding anyway.

    There is also situations like you're wanting to record in high quality HD, for watching directly on your HTPC - but for viewing on iPhone/iPad devices, maybe your wifi network cant stream at that bitrate, or you're trying to stream it remotely over the Internet, where you need its resolution/bitrate reduced for smooth playback on the client, which would mean you want to do the transcoding anyway...

    That said, you can probably force your setup to pass through the H.264 stream without transcoding it. You'd probably need to edit config.xml, setting the <TranscodeHLS> to something like:
    <TranscodeHLS>-y [SEEK] -i [SOURCE] -map_metadata -1 -threads 0 -map 0:0 -map 0:1 -map -0:s -vcodec copy -flags -global_header -sc_threshold 0 -codec:a:0 aac -strict experimental -ac 2 -ab 128000 -af \"adelay=1,aresample=async=1\" -hls_time 3 -start_number 0 -hls_list_size 0 -y [TARGET]</TranscodeHLS>

  3. #3
    Join Date
    Jan 2006
    Thanks for the quick reply Sub. I'll give it a try.

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