What are similar compressors to the RAR algorithm?
I'm interested in compressing videos (for example, avi) and images (for example, jpg)
Winrar reduced an avi video (1 frame/sec) to .88% of it's original size (i.e. it was 49.8MB, and it went down to 442KB)
It finished the compression in less than 4 seconds.
So, I'm looking to a similar (open) algorithm. I don't care about decompression time.
Compressing "already compressed" formats are meaningless. Because, you can't get anything further. Even some archivers refuse to compress such files and stores as it is. If you really need to compress image and video files you need to "recompress" them. It's not meant to simply convert file format. I mean decode image or video file to some extent (not require to fully decoding), and apply your specific models instead of formats' model with a stronger entropy coder. There are several good attempts for such usages. Here is a few list:
PackJPG: Open source and fast performer JPEG recompressor.
Dell's Experimental MPEG1 and MPEG2 Compressor: Closed source and proprietry. But, you can at least test that experimental compressor strength.
Precomp: Closed source free software (but, it'll be open in near future). It recompress GIF, BZIP2, JPEG (with PackJPG) and Deflate (only generated with ZLIB library) streams.
Note that recompression is usually very time consuming process. Because, you have to ensure bit-identical restoration. Some programs even check every possible parameter to ensure stability (like Precomp). Also, their models have to be more and more complex to gain something negligible.
Compressed formats like (jpg) can't really be compressed anymore since they have reached entropy; however, uncompressed formats like bmp, wav, and avi can.
Take a look at LZMA
Related
I'm packing some image resources for my game, and since this is a typical "compress once, decompress multiple" scenario, LZ4 High Compression fits me well (LZ4HC take longer time to compress, but decompress very fast).
I compressed a bitmap from 7.7MB to 3.0MB, which looks good to me, until I found that the PNG version is only 1.9MB.
I know that LZ4 HC do not have the ratio that deflate (which is used by PNG) does, but the ratio 2.55 vs 4.05 looks not right.
I searched and find that before compressing, PNG format will perform a Filtering operation, though I don't the details, it looks like that the Filtering move manipulate the data to fits the compress algorithm better.
So my question is:
Do I need to perform a filtering move before compressing using lz4?
If yes, where can I get a library (or code snippet) to perform filtering?
If no, is there any solution to make a PNG (or other lossless image formats) compress slow but decompress fast?
The simplest filtering in PNG is just taking the difference of subsequent pixels. The first pixel is sent as is, the next pixel is sent as the difference of that pixel and the previous pixel, and so on. That would be quite fast, and provide a good bit of the compression gain of filtering.
I was wondering if any lossless image compression format such as PNG comes with some kind of uniqueness guarantee, i.e. that two different compressed binaries always decode to different images.
I want to compute the hash of images that are stored in a lossless compression format and am wondering if computing the hash of the compressed version would be sufficient.
(There are some good reasons to compute the hash on the uncompressed image but there are out of the scope of my question here.)
No, that's not true for PNG. The compression procedure have many parameters (filtering type used for each row, ZLIB compression level and settings), so a single raw image can result in many different PNG files. Even worse, PNG allows to include ancillary data (chunks) with miscelaneous info (for example, textual comments).
Archives of JPEG files don't compress well, ostensibly because each JPEG is already highly compressed. However, when there is much redundancy between images (e.g., archived stills from a stationary camera), and the number of files is large (think thousands or more), there comes a point when failure to exploit the redundancies makes JPEG seem dramatically inefficient for files to be stored in archives.
What approach and archive format would give the best compression of JPEG files?
We have a project which will generate lots (hundreds of thousands) of .PNG images that are around 1mb. Rapid serving is not a priority as we use the images internally, not front end.
We know to use filesystem not DB to store.
We'd like to know how best to compress these images on the server to minimise long term storage costs.
linux server
They already are compressed, so you would need to recode the images into another lossless format, while preserving all of the information present in the PNG files. I don't know of a format that will do that, but you can roll your own by recoding the image data using a better lossless compressor (you can see benchmarks here), and have a separate metadata file that retains the other information from the original .png files, so that you can reconstruct the original.
The best you could get losslessly, based on the benchmarks, would be about 2/3 of their current size. You would need to test the compressors on your actual data. Your mileage may vary.
I need to know if it is possible to create a 30 second sample MP3 from a WAV file. The generated MP3 file must feature a fade at the start and end.
Currently using ffmpeg, but can not find any documentation that would support being able to do such a thing.
Could someone please provide me the name of software (CLI, *nix only) that could achieve this?
This will
trim out from Position 45 sec. the next 30 seconds (0:45.0 30) and
fade the first 5 seconds (0:5) and the last 5 seconds (0 0:5) and
convert from wav to mp3
sox infile.wav outfile.mp3 trim 0:45.0 30 fade h 0:5 0 0:5
Check out SoX - Sound eXchange
I have not used it myself but one of my friends speaks highly of it.
From web page (highlighted my me):
SoX is a cross-platform (Windows,
Linux, MacOS X, etc.) command line
utility that can convert various
formats of computer audio files in to
other formats. It can also apply
various effects to these sound files,
and, as an added bonus, SoX can play
and record audio files on most
platforms.
The best way to do this is to apply the 30-second truncation, fade in and fade out to the WAV audio data before converting it to an MP3. If your conversion library has a method that takes an array of samples, this is very easy to do. If the method only accepts a WAV file (either in-memory or on disk), then this is slightly less easy as you have to learn the WAV file format (which is easy to write but somewhat more difficult to read). Either way, applying gain and/or attenuation to time-domain sample data (as in a WAV file) is much easier than trying to apply these effects to frequency-domain data (as in an MP3 file).
Of course, if your conversion library already does all this, it's best to just use that and not worry about it yourself.