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tim_beynart
Level 7

How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

I am trying to capture timed metadata from an HLS live stream. Using IsTimedMetaData() on the roVideoPlayerEvent, the info available is formatted like this, with either a PRIV of GEOB key:

{
    PRIV: "7777772E6E6D3D2F436F6343486879756E5968564676435A33324B6341466B436869796B6(snipped)"
}


In Javascript, we use String.fromCharCode.apply(null, new Uint8Array(buf)) to translate the arraybuffer to a string. The string is a set of name/value pairs formatted like a URL querystring.
Is there a technique in Brightscript to achieve the same result?
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17 Replies
tim_beynart
Level 7

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

I made progress, in case anyone is in the same boat.
data = msg.GetInfo()
        if data.PRIV <> invalid
        ? "+++++++++++++++++++++++++++++++"
        ? "+++++    TIMED METADATA   +++++"

            ba = CreateObject("roByteArray")
            ba.FromHExString(data.PRIV)
            strg = ba.ToAsciiString()
            ? strg
         ? "+++++++++++++++++++++++++++++++"
        end if
'will print out something like

+++++    TIMED METADATA   +++++
www.nielsen.com/X100zdCIGeIlgZnkYj6UvQ==/-NTXplxffzT26A8zx85cow==/DLUCGQsuwoqz1cqXPQA8xhYmQDTfpKUllSnSwH0mLRmQ4FmN5_oyKk1YgRwu_7Go7HwfmZa7ru8LN_PhMUHpHAcY_ztXgCb6rcSpn9JIES4P4COWfiIeY6T3ILuUMUvetbBcX100zdCIGeIlgZnkYj6UvVg_T7JYP0-8OWM=/00000/51385/00
+++++++++++++++++++++++++++++++
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tim_beynart
Level 7

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

GEOB is still giving me headaches. It ends up all our important data is provided as a GEOB frame. However, using the same code, I never get anything more than "?application/json" as the value:

? "+++++    TIMED METADATA   +++++"
        data = msg.GetInfo()
        ?data
       
         if data.GEOB <> invalid

            ba = CreateObject("roByteArray")
            ba.FromHExString(data.GEOB)
            strg = ba.ToAsciiString()
            ? "GEOB"
            ?strg

        end if



prints this in the console:

+++++    TIMED METADATA   +++++
<Component: roAssociativeArray> =
{
    GEOB: "036170706C69636174696F6E2F6A736F6E006B6579732E6A7300416E7661746F7300747970653D63617074696F6E267074733D3532343734343934267061796C6F61643D747325334435323437342E343934253236746578742533444D4144454C45494E452532353230414C42524947485425323532304A4F494E454425323532304D4525323532304F4E253235323026696E73747265616D3D31"
}
GEOB
?application/json
+++++++++++++++++++++++++++++++
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belltown
Level 7

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

I think that's because your GEOB thingy contains null characters. As far as BrightScript is concerned, as soon as it finds a null character in a string, it treats it as the end of the string.

Before you convert to a string you'll have to go through the byte array extracting each null-terminated piece of string data, then convert each of those to a string.
https://github.com/belltown/
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Roku Employee
Roku Employee

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

As Belltown says, the hex encoded string represents the binary data of the GEOB frame.
You would have to decode that into components yourself, e.g. using roByteArray.

http://id3.org/id3v2.4.0-frames 4.15. General encapsulated object =>
Text encoding $xx
MIME type <text string> $00
Filename <text string according to encoding> $00 (00)
Content description <text string according to encoding> $00 (00)
Encapsulated object <binary data>
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tim_beynart
Level 7

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

Thanks! You guys rock!
I am now officially out of my depth. Any pointers on how to decompose the byte array into its components?
...off to StackOverflow... Smiley Wink
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tim_beynart
Level 7

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

Got it, thanks for the help! I just split the HEX at "00" and run each string through the translation process. Works like a champ.
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EnTerr
Level 8

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

"RokuKC" wrote:
As Belltown says, the hex encoded string represents the binary data of the GEOB frame.
You would have to decode that into components yourself, e.g. using roByteArray.

Any chance the un-support of \0 in strings can be fixed? As far as i can tell the \0 arcane quirk is not even documented.

I can imagine the (d)effect stemming from ye olde C but string libraries don't suffer from that since... forever. Even easier if rolling-your-own strings - which seems is what the Co. has done, because UTF-8. Shirley, i am serious - i remember the end of last century writing a script engine for a most unusual hardware^ where we had just barebones C to boot - so as part of it i had to write a simple string library supporting \0. It was no BFD.

As a side effect, that will fix the embarrassment of len(str) being O(n)... <wink-wink, nudge-nudge>

(^) Tandem NonStop - a fault-tolerant system used by banks/stock exchanges with no single point of failure (in some configurations having 3 CPUs and 3 banks of RAM working in tandem on the same thing, with the bus hardware arbitrating majority vote every cycle and isolating defective ones) - all components were hot-swappable, no restart; yes - RAM and CPU were replaceable with no down time :twisted:
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Roku Employee
Roku Employee

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

"EnTerr" wrote:

Any chance the un-support of \0 in strings can be fixed? As far as i can tell the \0 arcane quirk is not even documented.


I think it is unlikely that Roku would add support for embedded chr(0) characters in BrightScript strings.
In my opinion there isn't a valid use case for it. If you need to work with binary data, roByteArray is your best bet.
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EnTerr
Level 8

Re: How to translate ID3 PRIV or GEOB to readable strings from HLS live stream?

"RokuKC" wrote:
I think it is unlikely that Roku would add support for embedded chr(0) characters in BrightScript strings.

Hm, let me correct myself - i implied the only way to allow for U+0000 is by re-implementing String type with length_counter field. I was wrong - turns out there is a wickedly clever way to represent \0 in UTF-8 as 0xC0 0x80 as to avoid ever using the dreaded 0x00 octet. See Modified UTF-8.

However, if i try to do that through roByteArray, bizarre things happen:

Brightscript Debugger> ba = createObject("roByteArray"): ba.fromHexString("c080")
Brightscript Debugger> s = ba.toAsciiString(): ? len(s), s, asc(s)
1              ??               63

What's going on here? Seems like a bug - len() is correct but the rest is whacked?
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