SPLIT COMPRESSION FORMAT FOR NBTV VIDS

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SPLIT COMPRESSION FORMAT FOR NBTV VIDS

Postby daniel gosson » Tue Jun 26, 2007 11:05 am

Here is an experiment that I would appreciate some feedback from. The problem with compressing NBTV signals is that the video track has completely different compression requirements to the audio. The attatched video makes the best of this problem.
The video track has been converted to 8 bit and zipped. the audio track has been converted to MP3. This results in a visually lossles 8.45 minute video with sound that fits into about 11 mb.
Only moderate skill is required to reattatch the sound & video back together with a sound editor like sound forge. Dead Easy.
Please let me know if this works for you.
Kind Regards Daniel Gosson.
Attachments
DANS 25 7 NBTV VID (split).zip
(11.26 MiB) Downloaded 130 times
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Postby gary » Wed Jun 27, 2007 12:01 am

Yep works fine for me.

Note that in another thread I offered to write some software to make this process more-or-less automatic. If the two files are merged as separate files into a zip file you could chose the software for convenience or do it by hand if you want to. If there is enough interest I'd still be interested in doing it.
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Postby DrZarkov » Wed Jun 27, 2007 12:10 am

Unfortunally it is not suitable for a streaming video format, and even for download it is not simple enough. How about converting the videosignal to MPEG (not layer 3, but plain "MPEG 1".) like it is used on videoCDs? Did anybody tried other compression-methods like AAC+ or Ogg Vorbis?
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Postby gary » Wed Jun 27, 2007 12:52 am

DrZarkov wrote:Unfortunally it is not suitable for a streaming video format, and even for download it is not simple enough. How about converting the videosignal to MPEG (not layer 3, but plain "MPEG 1".) like it is used on videoCDs? Did anybody tried other compression-methods like AAC+ or Ogg Vorbis?


No it wasn't intended as a streaming format as that requires that the same temporal quantity of video and audio arrive at the same time. This would require being able to specify the exact amount of compression be applied to match the video packets with the audio packets.

However it is still a valid technique for downloading and also storing in
low capacity storage areas. Although I suppose you could download them as compressed AVI's or WMV's or whatever and convert them to NBTV on demand.

No form of lossy audio compression will work *reliably* on NBTV because it throws away information that is not necessary for audio but may well be essential for video. You may get away with some material but sooner or later it won't work. The MPEG you see on video CDs is MPEG for video, and whilst it is lossy it is throwing away things that are not necessary for video rather than audio, and of course works on adjacent pixels in the video (and even pixels in other frames), these pixels are not adjacent in the NBTV wave file. When compressing video streams the video is always buffered into frames, processed, and then restreamed. BTW, the amount of compression that can be achieved with video is generally much higher than can be achieved with audio which is fortunate otherwise digital TV would not be as successful.

Of course a compression algorithm that knew about the NBTV wavefile could be written to compress it as video rather than audio. Nobody has bothered to write one yet though, I wonder why? :-)
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To compress or not?

Postby Steve Anderson » Wed Jun 27, 2007 1:26 pm

gary wrote:Of course a compression algorithm that knew about the NBTV wavefile could be written to compress it as video rather than audio. Nobody has bothered to write one yet though, I wonder why? :-)


Well, *Fidgeting in chair* is compression really needed for NBTV? As I have mentioned elsewhere lossy compression gives me indigestion.

The file that I posted called 8RevGrey.wav shrank from 2.8MB to just 28kB using lossless Winzip. But this is a very simple file with no sound and a repetitive waveform, so arguably not representative.

So I downloaded DANS CG NBTV VID 2.zip which as posted is 4.2MB this expanded to 13.1MB when unzipped. Almost a 3:1 ratio, lossless.

With ADSL, cable and fibre connections that most have and the vast real estate of CDs and DVDs I don't see the need to use lossy compression. Sorry.

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RE COMPRESSION

Postby daniel gosson » Tue Jul 03, 2007 10:46 am

For some reason this incredible reduction in filesize with zipping only works on a mono silent video. Stero files will only knock off a tiny percent, not worth it realy.
I have trird other lossy formats. Ogg vorbis is much the same as mp3, but does not seem to have the crosstalk problems that stero mp3 has. IMA ADPCM is by far the best lossy format I have tried so far, the artifacts are very much smaller than MP3. I did post some IMA ADPCM vids onto this forum but concluded that this was not a popular method due to the low download numbers.
I do believe that NBTV compression is necasary as it is the only way to fit a video of a worthwhile lenght into 20 Megabytes (this forum limit). plus, would you download the original sise file of 80 MBs for 8 mins? I wouldnt.
MPEG 1, 2, 4 etc is the wrong aspect ratio & video cd resulution is 1.5 megabits anyway, the same as stero uncompressed wav. Surprizingly, 1.5 megabit video & less has artifacts big enough to see on the finnished NBTV vid, I have tried it.
IMA ADPCM does not strip inaudible sound from the recording as mp3 does.
Very briefly it does something like this; Instead of measuring every single sample as in ordinary PCM, Every 2nd one is measured directly. A pediction is made on the probable value of the intermediate samples based on the actual values of the ones either side of it.
Now the predicted samples are measered directly as well. As the predictions are extremely acurate, the difference between the predicted value & the actual measured value is so small it can be recorded as 4 bit audio, thus compressing 4 to 1.
All samples then go through this process reducing 16 bit to 4 bit.
Almost all players wil play IMA ADPCM & I have yet to find a sound editor that doesnt support it. In fact, you can convert to & from WAV & IMA ADPCM with windows sound recorder. Easy.
Daniel Gosson.
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Postby DrZarkov » Tue Jul 03, 2007 5:00 pm

Sounds good to me. How about streaming? It would be nice to set up a webserver with a "real programme".
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