CODEWITHSUNDEEP
javascriptarraysstringperformancecompression
Lapsio
Lapsio

Reputation: 7094

float Array compression in javascript

I saw quite many compression methods for js but in most cases compressed data was in string and it contained text. I need to compress array of less than 10^7 floats in range 0-1.

As precision is not really important eventually i can save it as string containing only numbers 0-9 (containing only 2 first digits after decimal of each float). What method would be best for data like this? I'd like to have smallest possible output but also it should't take more than ~10 sec to compress this string it's about up to 10 000 000 signs when saving 2 digits per float.I saw quite many compression methods for js but in most cases compressed data was in string and it contained text. I need to compress array of less than 10^7 floats in range 0-1.

As precision is not really important eventually i can save it as string containing only numbers 0-9 (containing only 2 first digits after decimal of each float). What method would be best for data like this? I'd like to have smallest possible output but also it should't take more than ~10 sec to decompress this string it's about up to 10 000 000 signs when saving 2 digits per float.

Data contains records of sound waveform for visualization on archaic browsers not supporting Web Audio API. Waveform is recorded at 20 fps on Chrome user client, compressed and stored in server db. Then send back to IE or ff after request to draw visualization - so I need lossy compression - it can be really lossy to achieve size able to be send with song metadata request. I hope compression on wav -> mp3 64k level would be possible (like 200:1 or something) noone will recognise that waveform is not perfect on visualization, I thought maybe about saving theese floats as 0-9a-Z it gives 36 instead of 100 steps but reduces record of one frequency to 1 sign. but what next, what compression to use on this string with 0-Z signs to achieve best compression? would lzma be suitable for string like this? compression / decompression would run on web worker so it doesn't need to be really instant - decompression like 10 sec, compression doesn't matter - rather less than one song so about 2 min

Upvotes: 1

Views: 1296

Answers (1)

Cort Ammon
Cort Ammon

Reputation: 10903

Taking a shot in the dark, if you truly can rely on only the first two digits after the decimal (i.e. there are no 0.00045s in the array), and you need two digits, the easiest thing to do would be multiply by 256 and take the integer part as a byte

encoded = Math.floor(floatValue * 256)
decoded = encoded / 256.0

However, if you know more about your data, you can squeeze more entropy out of your values. This comes out to a 4:1 compression ration.

Upvotes: 6

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