Encoding tv to xvid in realtime?

mr-simon · Posted: Fri Feb 02, 2007 12:36 pm Post subject: Encoding tv to xvid in realtime?

I have a freevo-based PVR and media organiser that does everything I want it to, except when it comes to recording TV. I can record my DVB-T stream directly to disk, but it takes up a *lot* of space. I've tried having mencoder transcode to xvid on the fly, but my computer can't keep up and I drop frames. (It's an old sempron 1800 or so)

What is the minimum CPU spec that I would need to upgrade to, to accomplish this?

I realise that I could transcode the files post-recording with some kind of script, but I'd like to have it happen in realtime if it's possible.
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frostschutz · Advocate Joined: 22 Feb 2005 Posts: 2977 Location: Germany

Does it have to be xvid? I'm not up to par with codecs nowadays anymore, but usually newer codecs achieve better compression & quality with higher CPU requirements. I'd bench all codecs there are (even or especially the old ones), maybe try a high bitrate MPEG-2 and see if that works in realtime. The result won't be small, but anything that is not quite as huge as a raw stream should probably be sufficient. You can then re-encode the MPEG-2 or whatever stream to whatever cpu intensive killer machine codec you like afterwards (maybe at the cost of some little extra quality due to encoding twice, but that's the same you get with dvd rips, so it's probably not that much of a problem).

There is hardware for encoding stuff on the fly in real time (mpeg de/encoder cards), maybe there even are such cards for xvid nowadays, I don't know. If you always want to encode the latest / highest quality codec in realtime, even the fastest desktop cpu won't be sufficient, as these codecs are optimized for size & quality, not encoding speed or even on the fly encoding. Even xvid requires you, if you want optimal results, to encode with two passes.

mr-simon · Posted: Fri Feb 02, 2007 4:00 pm Post subject:

IIRC the data coming in (a DVB-T transmission) is already high-bitrate mpeg2. The data coming in is, on average, somewhere over a gigabyte per hour. It's not the end of the world storing that much, but my disk does tend to fill up quickly.

If it's simply impossible to transcode to xvid on the fly, is there an 'interim' codec that might be a good tradeoff between size/speed?
_________________
"Pokey, are you drunk on love?"
"Yes. Also whiskey. But mostly love... and whiskey."

Gusar · Posted: Fri Feb 02, 2007 6:00 pm Post subject:

frostschutz · Advocate Joined: 22 Feb 2005 Posts: 2977 Location: Germany

rtomek · Posted: Sat Feb 03, 2007 3:41 pm Post subject:

I 2nd frostschutz... A huge disk would be a way better idea than encoding on the fly in xvid. I have tivo, but i bought a huge disk drive to put in there so that I could get the highest quality recording then do what I want with it when I transfer it to the computer. Disk space is cheap nowadays and if you have 100 hours of stuff (120 GB drive in your case) and fill up your drive you probably won't get around to watch most of that stuff anyways and you can start deleting shows. Also, 1 GB per hour seems small... that is the rate I get on my tivo when I use lowest quality recording, my full quality takes something like 3 GB/hr, so you should be happy with only 1 GB/hr .