I need to append 2 video files by appending their NSMutableData as I have already done this with audio files and it is done correctly but not with video files.
It may be because data bytes contain some header info and I will need to remove these bytes from the 2nd video but I don't know that how many bytes should I remove?
You haven't told us the file format in question, but generally:
Look up the specification for the file format in question and find out what the header looks like. Then code a solution based on this information.
There are many resources on the net with file format information, but one place you might want to look is http://www.wotsit.org/.
Related
This question is about extraction of metadata only.
Is it required for exiftool to get a complete file for propperly working?
Scenario:
I want to extract the metadata of a 20 GB video file. Do I need to provide exiftool with the complete file (via stdin), or is it enough to provide it with a certain amount of bytes.
Motivation:
I am programatically (golang) calling exiftool in a streaming context and want to have the extraction as fast as possible. Magic numbers for filetypes work with the first 33 bytes and I am wondering if that is possible with the exiftool metadata as well.
The answer depends upon the file and the location of the metadata within that file.
There are a couple of threads on the subject on the ExifTool forums (link 1, link 2) and Phil Harvey, the author, says that about half the time the in the case of MP4/MOV videos, the metadata is at the end of the file.
Using the -fast option might help. I've done some quick tests using cURL and a large image file (see the second to the last example under Piping Examples) and in that case cURL didn't download the whole image file, just enough to extra the metadata. It might be different with a video file though, as I haven't tested that situation.
I need to convert my SFF file to PDF, then i need verify the document. i.e SFF file and converted file.
For that, I think to convert SFF file to image file and PDF file to image file.
Then comparing the both file using image processing.
To do this method:
Im searching for a program to convert SFF to BMP
Does anyone know such a program or has another idea how to do the job?
Thank you in advance...
Looks like you need reaConvertor. It　appears to be a matured tool you can rely on. There is an online version of the tool here
I think:
https://github.com/Sonderstorch/sfftools
will do what you need (convert sff -> tiff/jpeg/..) and then you can use imageMagic (for example) to go to PDF.
Clearly not a current well used image format, however if you have legacy.sff Structured Fax Format, they are similar (not exactly identical) to a Monochrome G4 format.
By far the simplest programmable method to convert is using IrfanView which can Read Modify and Resave as other formats in batches.
Out put can be any other modern image type including Mono.BMP, G4.fax or as PDF (with or without GhostScript)
I would like to play some kind of text-to-speech with only numbers. I can record 10 wav files, but how can I combine them programmatically ?
For instance, the user types 1234, and the text-to-speech combines 1.wav with 2.wav, 3.wav and 4.wav to produce 1234.wav that plays "one two three four".
1) create a new destination sample buffer (you will want to know the sizes).
2) read the samples (e.g. using AudioFile and ExtAudioFile APIs) and write them in sequence to the buffer. You may want to add silence between the files.
It will help if your files are all the same bit depth (the destination bit depth - 16 should be fine) and sample rate.
Alternatively, if you have fixed, known, sample rates and bit depths for all files, you could just save them as raw sample data and be done in much less time because you could simply append the data as is without writing all the extra audio file reading programs.
The open source project wavtools provides a good reference for this sort of work, if you're ok with perl. Otherwise there is a similar question with some java examples.
The simplist common .wav (RIFF) file format just has a 44 byte header in front of raw PCM samples. So, for these simple types of .wav files, you could just try reading the files as raw bytes, removing the 44 byte header from all but the first file, and concatening the samples. Or just play the concatenated samples directly using the Audio Queue API.
I want to copy a part of the audio file, given the starting and ending point(in terms of time which I'll convert to packets or frames-is the conversion right?), and create a new audio file for the copied snippet. How do I copy?
Please advice.
Regards,
Namratha
For what file format(s)?
For the simplest and common .WAV (RIFF) file format, you can just copy the canonical 44-byte header (after checking to make sure the file is using only this simple format), update with the target file length, and then copy a selected sub-range of bytes (multiply time by sample rate by frame size) from the source file, and append that PCM data to the copied header. Apple's codec does not complain about audio files patched together this way.
For other formats, you might be able to convert them either to a simple WAVE file, or to an array of raw PCM samples of suitable sample rate, data type and endianess, and then do the above.
I am engaged in preparing an application regarding reading the .epub files in iPhone. Where can I get the reference for sample applications for unzipping and parsing the files? Can anyone guide me with a best link? Thank you in advance.
An .epub file is just a .zip file. It contains a few directory files in XML format and the actual book content is usually XHTML. You can use Objective-Zip to unzip the .epub file and then use NSXMLParser to parse the XML files.
More info: Epub Format Construction Guide
On top of Ole's answer (that's a pretty good how-to guide), it's definitely worth reading the specification for the Open Container Format (OCF) - sorry it's a word file. It's the formal specification for the for zip structure used.
In brief you parse the file by
Checking it's plausibly valid by looking for the text 'mimetype' starting at byte 30 and the text 'application/epub+zip' starting at byte 38.
Extracting the file META-INF/container.xml from the zip
Parsing that file and extracting the value of the full-path attribute of the first rootfile element in it.
Load the referenced file (the full-path attribute is a URL relative to the root of zip file)
Parse that file. It contains all the metadata required to reference all the other content (mostly XHTML/CSS/images). Particularly you want to read the contents of the spine element which will list all content files in reading order.
If you want to do it right, you should probably also handle DTBook content as well.
If you want to do this right, you need to read and understand the Open Packaging Format (OPF) and Open Publication Structure (OPS) specifications as well.