pcHDTV :: View topic - Using vlc to downconvert a pchdtv .ts file

johnclubvec

I like the vlc media player (http://www.videolan.org) a lot. I have found a one-line command using vlc which converts a recorded pchdtv .ts file into a very good quality lower-density format, with good audio sync throughout, and without using any hard-drive hogging intermediate or temporary files. And I've run it successfully on a long (one-hour) file. I won't claim that the converted file meets the specs for a standard mpeg or dvd-type file, because I don't know anything about formats or how to tell them apart. I only know the result looks and sounds pretty good. I'd be curious if others would try this thing out and see what it could do for them.

The bad news is that on my 2.6 GHz Pentium 4 using 99% of CPU, the conversion takes longer than real-time (that is, longer than it takes to play the original file). The good news, as mentioned, is that the video and audio quality are awfully good, it uses no temporary files, and the converted file is only about 15% the size of the original.

vlc gives me this information about the converted file, in case my betters can interpret it:

main debug: using demux2 module "ps"
libmpeg2 debug: 720x416, aspect 768000, 29.971 fps
main debug: picture in 720x416, chroma 0x30323449 (I420), aspect ratio 16:9
mpeg_audio: MPGA channels:2 samplerate:48000 bitrate:192

In the example here I will call the original .ts file "input.ts." It is a 1080i file recorded from my local PBS-HD channel. We'll also say that we are interested in processing subchannel 3 of that file (which will appear in vlc as "--program"). I will call the output file "output.mpg." Here is the command-line, followed by a glossary of terms. Please note that on my machine, I must run vlc as root to do this conversion. The following is all one long command line:

vlc "input.ts" --program 3 --sout '#transcode{vcodec=mpgv,vb=2048,scale=0.375,acodec=mpga,ab=192,channels=2}:standard{access=file,mux=ps,url="output.mpg"}'

Glossary of terms:
"vcodec=mpgv" I believe this means the video codec will be MPEG2.
"vb=2048" The video bitrate in kb/second.
"scale=0.375" Only one number is used to scale both horizontal and vertical. I picked the width to be the controlling factor. The original width is 1920, so 720/1920 = 0.375.
"acodec=mpga" The audio codec will be mpg.
"ab=192" The audio bitrate in kb/second.
"channels=2" Two audio channels.

The rest of the line has to do with outputting to the file.

Again, I welcome comments.

Guest

Thanks for the post - this worked well for me using VLC 7.2.

However, during transcode I am preserving the AC3 stream and the right-rear and center channels are being swaped.

I tried upgrading to the latest VLC version (I think I read somewhere that the AC3 problem was fixed), but the transcode command no longer works:

vlc "army-navy.ts" --program 2 --sout '#transcode{vcodec=mpgv,vb=4096,scale=0.375,acodec=a52,ab=384,channels=6}:standard{access=file,mux=ps,url="army-navy-6c.mpg"}'
VLC media player 0.8.1 Janus
[00000190] main private error: no sout stream module matched "transcode"
[00000189] main stream output error: stream chained failed for `transcode{vcodec=mpgv,vb=4096,scale=0.375,acodec=a52,ab=384,channels=6}:standard{access=file,mux=ps,url="army-navy-6c.mpg"}'
[00000188] main input error: cannot start stream output instance, aborting

Has anyone been able to get transcode working with VLC 8.2?

Thanks
Dave

Scott Larson

This is scaling HD down to SD resolution, right?

Guest

Yes it is. Transcoding HD to SD while keeping the 5.1 audio intact

Dave

Scott Larson

Why do people want to scale down HD to SD?

I can convert filmed HD material to 15%-25% of its original size by using an inverse telecine filter (or decimate to throw away duplicate frames) to turn it back into 24 fps progressive and compressing it with Xvid. It's still in its original resolution and there's almost no difference in quality in the compressed version and I keep the AC-3 sound too. This lets me burn three or four episodes of a TV series on a DVD+R.

OK, it does take a very very long time to compress, about ten hours for 45 minutes. I'm sure non-filmed material won't compress nearly as well.

dacid

Because I don't have a HDTV Smile

The downgraded picture still blows away the NTSC broadcast equivelant, not to mention that the 5.1 audio is great.

Dave

Scott Larson

But when you get an HDTV you'll wish you had compressed the files in their original resolution, especially since it would have made the files only 10%-15% larger.

Just like when I got a real 5.1 receiver a few weeks ago, I was glad I had kept the original AC-3 streams in every show I had archived for the past year instead of compressing them with MP3 or lame.

dacid

I agree completely, which is why I am keeping the original ts files for the happy day when I get a HDTV Smile

In the meantime however, I'd like to enjoy the "DVD like" quality of a downconverted HD stream and 5.1 sound on my POS NTSC TV.

Scott Larson

But you can enjoy the DVD quality by just downscaling the original ts files in real time. You don't have to convert the files to play them at a lower resolution. Your 2.6 Ghz Pentium 4 can downscale HD without breaking a sweat.

Guest

Yeah, I would do that, but - my PVR box is a P3 500mhz that uses a PVR-350 to decode MPEG2.

The PVR-350 can't handle the high def MPEG2 TS file, so my only option is to downconvert first.

mwahal

mwahal

I'm using VLC media player 0.8.2-test1 Janus. Getting tons of messages.

The output file is growing, so it must be writing something. Any idea why these messages are coming?

Thanks

Mudit

libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PATCallBack called
libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PMTCallBack called
libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PATCallBack called
libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PMTCallBack called
libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PATCallBack called
libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PMTCallBack called
libdvbpsi error (PSI decoder): TS discontinuity (received 0, expected 1)
[00000265] ts demuxer debug: PATCallBack called

mwahal

anyone following the first post should note couple of points.

1. remove --program 3 option .. its very specific to his TS stream.
2. use :sout and then append vlc:quit at the end of command line. Then you can use it from a script
3. Always find your own scale= values and vb rate.

Thanks

Mudit

mwahal

Scott,

Can you please give command lines how you do it ? Or point to a howto/faq ?

Thanks
Mudit

Scott Larson