we know movie atom in a MP4 container file stores information that describes a movie's data. I am wondering if a single MP4 file can contain more than one movie atoms (atom type of 'moov')?
anyone knows? Thanks
A valid MP4 file may only contain one single 'moov' box. This is stated in 8.2.1 of the ISO 14496-12 specification:
The metadata for a presentation is stored in the single Movie Box which occurs at the top-level of a file.
Normally this box is close to the beginning or end of the file, though this is not required.
If you are using fragmented MP4 files the role of the 'moov' is mostly played by 'moof' boxes and those typically exist multiple times.
Related
I have to play various mp3 files on a given software without showing any information that could lead to the recognition of the played track (some kind of quiz). For that, I want to change the displayed track length to an arbitrary value. I can easily change up standard ID3 tags like "name", "artist" and so on. But changing the displayed track length seems to be more tricky, though...
Edit (after Vikram's response):
So far, I was able to manipulate the displayed track length by modifying the 'xing' header in a vbr encoded mp3 file. More precisely, I changed the bytes in the 'number of frames' section with a hex editor which lead to an mp3 that showed a modified track length according to:
Track length = Number of Frames * Samples Per Frame / Sampling Rate
with the file still being correctly played. This approach seems to work for winamp, vlc player and windows in general. Unfortunately, it does not seem to work for the proprietary software I have to use. When using that software, somehow the original track duration is still identified because a different calculation method is applied.
Any other ideas on how the track duration could be calculated resp. fooled into displaying an arbitrary value?
Thanks!
YES and NO.
Most of the .mp3 files have this extra info besides ID3 in XING header, which contains duration of the file.
You can modify this header to put wrong info.
Or you can simply remove this XING header!
There are two types of .mp3 files: CBR and VBR.
CBR is most common. So, using bitrate info, players still can estimate length of the audio for CBR.
For VBR this is not always correct!
So, the audio file you had was most likely an VBR encoded mp3 without XING header.
The track length is calculated by parsing the whole MPEG audio stream, a fairly straight forward process. XING (or similar) headers (correctly: frames) exist as a help like an additional index for seeking in the file, but it is not mandatory; it also only exists because 25 years ago in most cases it would have taken too much performance to fully parse files and keeping relevant data in memory when VBR was "invented". Metadata, where you could define incorrect track lengths (like the TLEN frame thru ID3v2) aren't mandatory either.
So: it's not possible. You rather found software/players that opt for performance without assuring everything they spot. Also no other file/stream format comes to my mind where a track length is mandatory and cannot be calculated by parsing the file.
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/.
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 am uploading many files to server where I need to enter frames resolution - it's much inconvenient to do it "manually" - open each file and then check their properties.
I would like to get a list of all movie files names (in .mpg and .swf format) with information about their screen resolution from windows command line (or PowerShell, or Linux console). How I can do it?
Look at midentify (mplayer tools); The output is not pretty but can easily be parsed so you can present it in the desired format
note: midentify is a wrapper around mplayer -identify IIRC
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.