Introduction

Some notes on different aspects of Digital Video - both as broadcast and, perhaps later, as on DVD. 
 

Broadcast & downloaded DTV

 
HD video codec, reported as "avc" by the KM Player, as H264 by the VLC Media Player, and not shown as variable bit rate (vbr).

HD audio codec, reported as AC-3 with no bit size by the KM Player.

Video - vbr - variable bit rate

Audio - nar - narrative audio
           vic - visually impaired commentary

Questions arising

1. The Dr.Who I recorded in a variety of ways in addition to the recorder downstairs.  I have iPlayer downloads which are 1280 x 720 pixels, and display quite well on my TV (played through a PC at 1360 x 768 pixels).  I recorded the HD versions from satellite, unfortunately messing up the main broadcast as I selected the "Narrative Audio" instead of the plain audio! Arrgh!  However, having recorded it with Win-TV from Freeview, I wanted to trim the beginning and end parts just for neatness. Imagine my surprise when the main program shrunk from 2.44GB to 1.52GB, and the "confidential" shrunk from 2.17GB to 1.26GB.  Any idea what might be going on here?  Both files seems to be identical when played.  The change is too much to be from just dropping an odd sound track, isn't it?
     
2. The KM Player does some times produce picture break-up, and I think John said that was a problem he found.  So far I have yet to find the exact circumstances when this happens, although I do recall seeing it at least once.
     
3. I recorded a 1 hour radio program from Freeview (Radio 4) as we were out of the house, and it had a friend's daughter in a discussion.  I was surprised that the file size came out to about 1GB, as if TV had been recorded as well.  Extracting the audio track alone it was about 89MB.  Is this typical of radio on Freeview, or is Win-TV at fault?  As I don't do much recorded radio, this isn't important.  A later run with TS Doctor also removed the unneeded video stream.
     
4. Perhaps even less important is that even though the VLC Media Player showed the audio as "mpga", the KM Player produced no sound when playing the track, and it's Media Info showed MPEG version 1 audio.
   
5. How does the DVB Recorder (Panasonic DMR-EX77) manage to expand a 2.5GB transport stream into a 3.9GB DVD?  And change the audio format from mpga into a52 (AC-3) at the same time?  Surely, it can't be decoding the stored video to analog, and re-digitising it for writing onto DVD?  Oh, dear!
    

DVD issues

Currently there are at least two issues relating to DVDs which I don't understand 100%.

File size for recorded DTT broadcasts

I think this is probably resolved, but it seems strange to me that a 1-hour SD broadcast which is a certain size when recorded from DTT via Win-TV (and so is just a transport stream, may occupy more space when you ask the recorder to write the program to DVD.  It's almost as if the recorder is decompressing the data and writing it with a reduced compression to the DVD.  I need to find a concrete example of this and put up more data.  Further tests have confirmed that something like this is happening - perhaps even that the video recorder is actually going via an analog process.
  

Quality when connecting a DVD player to a TV

One issue which has arisen recently is the best way to play a DVD.  When we got a hard-disk digital TV recorder, with DVD recording and playing capability, I must have initially used a SCART connection, and later an HDMI connection.  However, having recently got an off-air digital recording, which played nicely through a computer connected directly (so 1360 x 768 pixels), playing the same stream recorded onto a DVD, through the digital video recorder, gave a much worse picture in that MPEG artefacts were visible, and the image looked artificially sharpened.  Rather horrible, in fact.  I tried altering the "automatic" HDMI setting to 576p (I don't know what it was) and the result is a bit better, but still far too much sharpening for my taste.

• Playing the DVD on the DVD player, HDMI connection (auto) to the TV.  Highly visible sharpening and highly visible MPEG artefacts.
• Playing the DVD on the DVD player, HDMI connection (576p) to the TV.  Quite visible sharpening and some MPEG artefacts.
• Playing the DVD (or the original captured .TS track) on the computer set to the TV's resolution (1360 x 768 pixels).  No sharpening, few artefacts, but some motion judder, possibly due to the 60HZ refresh rate on the computer.

You can't win, can you?

Satellite TV reception - through the open window

As we already have a satellite dish outside for EUMETCast reception, and we don't yet have a second dish for domestic TV reception, we make do with a 35cm dish for getting domestic TV satellites like the clusters at 19šE and 28šE (Astra-1 and Astra-2).  Here it shown aligned to Astra-1 (19šE) for the German programs we wanted to watch on 2009 Dec 26.  Yes, we had a white Christmas!  A tripod is used to keep the white board horizontal, and pencil marks on the board show the best placement for the dish for the two satellites.  A slight tweak in elevation and LNB skew ensures best results when the dish is pointed at the other satellite.  A later addition has been a small barrier on the board to stop the window slamming against the dish, and a small hole underneath the board for the screw fitting on the camera tripod to locate into. Yes, I did try through the closed window and, no, the 10GHz signal didn't get through.

 

Copyright © David Taylor, Edinburgh

@gm8arv on Twitter

Last modified: 2012 Jun 12 at 17:46