Training creates hamming files that are the wrong length for PatternCUDA about vhs-teletext

[ali1234]

You probably did not record long enough to get every possible pattern. You
need a couple of hours.

On 14 Aug 2016 22:16, "grim-fandango" [email protected] wrote:

Hi Alistair,

I piped the output from training -g to raspi-teletext, recorded it on
Betamax, then captured it using vbicat. I then did a 'training -t' on the
vbi file, then on the output of that did --parity, --hamming and --full
(not sure if 'full' corresponds to debruijn, but that's a different matter).

The hamming file isn't a multiple of 1024 so PatternCUDA won't accept it.
Am I doing something wrong or is there an issue with the training script?

Thanks

Jason

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[grim-fandango]

I gave it two hours' worth, but I get the same error. The file is smaller too, at 762,489 bytes as opposed to 819,214.

[ali1234]

Do you get rejects when running training -t?

[ali1234]

The final training data files have a 14 byte header and then 25 bytes per recognized pattern. The hamming data should have 32768 patterns and the parity data should have 4096. Both multiples of 1024.

14 + (25 * 32768) = 819214
14 + (25 * 30499) = 762489

So you don't have a full set of patterns for some reason. That can only happen if some patterns weren't found in the raw training samples.

[grim-fandango]

It started out at 1% rejects then goes to 0%. When complete, it says: "1:30:11 : 5815928 lines, 1075/s total, 1073/s teletext, 0% rejected. "

If there are 1075 lines/s and 1073 lines/s are teletext, then it would seem that the rejection rate is actually 0.19%.

That was for a 2.5 hour sample.

[moonhouse]

See

vhs-teletext/teletext/vbi/map.py

Line 51 in 5dc0236

sys.stderr.write('%d:%02d:%02d : %d lines, %.0f/s total, %.0f/s teletext, %.0f%% rejected. \r' % (h, m, s, self.total, total_lines_sec, teletext_lines_sec, rejects_percent))

Format string is '%.0f%%'. 0.19% will be displayed as 0%.

[ali1234]

That is an acceptable error rate so I am not sure what is happening. The checksumming should prevent the pattern from being read incorrectly (eg with an offset).

What do your intermediates look like?

[grim-fandango]

Well, I've just run it again and it's generated a file of the right length. Not sure what was different this time. But thanks for looking at it and sorry for the wild goose chase. :-/

[ali1234]

That is extremely strange. To be honest I have forgotten how you even use the trainer bits. Any chance you could write some docs for it?

[grim-fandango]

I can only think that I ran it previously on Windows, although why that would matter I don't know.

My current problem is generating the parity training tables, as the training script literally grinds the machine to a halt after a while and I have to hard reset. I guess it's swallowed up all available RAM.

Sure, I'll write some docs, but I don't know much! Seems weird to write docs for it if I've not got it working yet.

[ali1234]

That is quite possible. It bucket sorts the packets in memory and then takes the average for each pattern at the end, so it will basically load the entire training file into RAM, which would be 10GB if you have 5 million lines. I had 16GB of RAM when I wrote this but I've upgraded since then!

[grim-fandango]

Yeah, just had a look at the code, there doesn't seem to be an easy way to spilt it up as it seems to require that it's all in RAM as you say. My training tables file is 29GB from a 14,894,235,648 byte VBI file. If each frame is 64K and contains 32 lines, then there will be 7.2M lines! There's 16GB RAM in this machine.

I have to try to chop down the original VBI file and run it again - I did about 2.5 hours of recording to get a file that size; maybe I over-egged it a bit!

[ali1234]

I might be wrong about the specifics actually. But for sure it needs a lot of RAM and will take a long time.

[ali1234]

Here is a braindump about how training works:

https://github.com/ali1234/vhs-teletext/blob/master/TRAINING.md

(I wrote it mostly from memory so it might be wrong.)