TIP: save hdd space with transcoding

[lif]

As you know, the HDD space fills very quickly and there is a little solution to this I have used. I don't post the complete code here yet (because I have to rewrite it a little bit), but the workflow/idea is here

1) edit postprocessing.bat to run comskip.exe on %1 and echo %1 >> \pvr\transcode.txt
2) edit \pvr\transcode.cmd to sth like that:
#!/bin/bash
f=`cat \pvr\transcode.txt`
for t in $f; do
\pvr\mencoder -oac mp3lame -ovc xvid -xvidencopts fixed_quant=4 $t -o $t.new
if [ %errorlevel% == 0]; do
del $t
ren $t.new $t
done
egrep -e $t \pvr\transcode.txt >\pvr\transcode
done
3) schedule a new task to be run on weekdays (Mo-Fr) at 9:00 \pvr\transcode.cmd and enable maximum run for 8h.

So what it does is after a new recording it runs comskip and marks out commercials and inserts new recording filename to processing queue. So, if you watch the recording before 9:00 on Monday, you will see original mpeg2 stream. At 9:00 on Monday morning it wakes up computer and transcodes as many mpeg2 streams from queue to xvid as it could in 8 hours and all left in queue are processed the next day (I choosed this time because the PVR is in living room and I don't want that the PVR makes any additional unwanted noise when my family is at home). It keeps the mpg extension on files and in original location. So, if you happen to playback this recording afterwards GB-PVR doesn't make difference that inside is avi not mpeg and allows to play back as normally it does (also commercial skipping and all other works).

All comments are welcome!

[krypton_john]

Nice!

Some comments:
- I don't think you'll be able to watch the xvids on MVP or PVR-350 tv-out
- I guess you have to install cygwin or mks tools to run all those *nix commands?

Cheers,
JohnO

[lif]

As I don't own MVP nor PVR-350 (I have PVR-150 and Pundit-R just fitting perfectly into my stereoanlage box), so can't comment on this topic much. But as I've read the threads here and followed the mailing lists of MythTV for months, I think that isn't impossible to pipe "live" xvid through mencoder/mplayer (or some filters or vlc?) to MVP or PVR-350 TV-OUT. In Linux world some people are watching other video formats than mpeg2 through PVR-350 TV-OUT. I did have couple of years ago Creative Dxr3 (which is also mpeg2 only) and with some chemistry and scripts I was able to watch some mpeg4 clips through it. Yes, bad thing is that it requires much CPU power to transcode formats on the fly and therefore HTPC hw isnt cool and quiet any more.

I'm with years of serious Linux background, so I like some scripting using *nix commands Whats bad of using cygwin anyway? You don't need to have full cygwin installed to use its commands, you need only cygwin1.dll and some other dll-s in the same directory as exe-s are, if you dont want to install the whole thing.

Although there is out there precompiled *nix utilities for windows which are statically compiled and won't need any external dll-s nor cygwin. The keyword in Google is "unix utils win32" or to give shortcut http://unxutils.sourceforge.net/ . Also mplayer/mencoder win32 static binary is available from mplayer official webpage http://www.mplayerhq.hu/homepage/design7/dload.html .

[arttext]

He, sounds great, especially for X-card owners since most codecs play on the Xcard too.
When can we expect the first release?

cheers, arttext

[jorm]

Great tip. I would love to use it but I need to find a transcoding solution first so I convert the xvid back to mpeg so I can stream it on my mvp.

How big are the xvids you create per hour?

If you figure out to convert xvid back to mpeg we can then play the file in xrecord. I can have xrecord launch a thread to start the transcoding command line. If the user pics a divx file.

I was playing with ffmpeg to do the conversion back and actually was able to convert a divx file back to mpeg2. All was good. The problem was when I tried to play it in gbpvr it would not play the video. I started playing with the audio kps

And got the video to play but the mpeg had no sound. Still working on that. We should update the wiki site with the tip, do you have an account if not I will update it for you.

[lif]

I guess I don't have wiki account.

Had you tried transcoding on the fly with VLC? (http://www.videolan.org) This allows to use divx/xvid as input and mpeg2 ts/ps as output. As it is opensource project it shouldn't be hard to borrow some code from this and give VLC guys a credit Or if won't want to play with source too much, it is also possible to drive VLC from command line (or open as hidden and/or minimized in background as GBPVR is in foreground).

So:
Step 1) Give VLC a xvided show as input (also subtitles are supported if watching movies)
Step 2) Set as output MPEG2 TS
Step 3) Send it for example as UDP to 127.0.0.1omething
Step 4) Redirect MPEG2 TS from UDP 127.0.0.1th to MVP or PVR-350 TV-OUT and thats it!
Shouldn't be hard to do!

[lif]

PS. I use for MPEG2 -> XviD settings for:
audio: lame mp3 - CBR 128kbps (as ABR goes sometimes after half an hour out of sync vith video)
video: xvid VBR so 45min talkshow (without commercials) will be about 350 MB (720x576 PAL x25fps x24bit). GSpot (http://www.headbands.com/gspot/) shows that average bitrate is about 1300 kb/s. Original filesize was about 2,2 GB. Raw saving will be about 6-8 times with quite a good quality! :-)

[bucknljake]

lif:

does comskip remove the commercials from the orig Mpeg1/2 recording first before encoding to xvid? also, does this create an intermediary file on the harddrive before incoding (concerned about how much HD buffer space I'd need)?

I've got an xcard so this set up would be sweet for me.

I've only got a 933mhz athlon in my HTPC, would it be better to run a script like this on one of my other desktops like an amd 3200+ (moving files back and forth, or mounting a network drive to the HTPC) ??

[sub]

No, it doesnt remove the commercials. It just creates a text file that lists the locations the commerical start and end.

[lif]

If you transcode with one pass, it don't make any intermediate file. But with one pass you coldn't have such a quality as with multiple passes. Also with multipass you could use VBR and have control of file size (predefined).

It depends how much you record shows per day, if only about hour or two, ~1GHz Athlon should transcode it in about 4 hours, if more then you may want to use faster CPU from other pc. In most cases you could just mount its drive (the network traffic used by encoding is quite low), but mounting keeps your htpc running. If you like to put your htpc to standby meanwhile, you need to copy files back and forward.