How can I load a memory stream into LibVLC? - file

I want to play a media file from a memory stream using LibVLC like so:
//Ideally it would go like this:
LibVLC.MediaFromStream = new MemoryStream(File.ReadAllBytes(File_Path));
Of course this is a very oversimplified version of what I want but hopefully it conveys what I am looking for.
The reason being that I want there to be a good amount of portability for what I'm doing without having to track file locations and such. I'd rather have a massive clump of data in a single file that can be read from than have to track the locations of one or many more files.
I know this has something to do with the LibVLC IMEM Access module. However, looking at what information I've been able to find on that, I feel like I've been tossed from a plane and have just a few minutes to learn how to fly before I hit the ground.

See my answer to a similar question here:
https://stackoverflow.com/a/31316867/2202445
In summary, the API:
libvlc_media_t* libvlc_media_new_callbacks (libvlc_instance_t * instance,
libvlc_media_open_cb open_cb,
libvlc_media_read_cb read_cb,
libvlc_media_seek_cb seek_cb,
libvlc_media_close_cb close_cb,
void * opaque)
allows just this. The four callbacks must be implemented, although the documentation states the seek callback is not always necessary, see the libVlc documentation. I give an example of a partial implementation in the above answer.

There is no LibVLC API for imem, at least not presently.
You can however still use imem in your LibVLC application, but it's not straightforward...
If you do vlc -H | grep imem you will see something like this (this is just some of the options, there are others too):
--imem-get <string> Get function
--imem-release <string> Release function
--imem-cookie <string> Callback cookie string
--imem-data <string> Callback data
You can pass values for these switches either when you create your libvlc instance via libvlc_new(), or when you prepare media via libvlc_media_add_option().
Getting the needed values for these switches is a bit trickier, since you need to pass the actual in-memory address (pointer) to the callback functions you declare in your own application. You end up passing something like "--imem-get 812911313", for example.
There are downsides to doing it this way, e.g. you may not be able to seek backwards/forwards in the stream.
I've done this successfully in Java, but not C# (never tried).
An alternative to consider if you want to play the media data stored in a file, is to store your media in a zip or rar since vlc has plugins to play media from directly inside such archives.

Related

Storing custom information in an audio/mp3 file

I want to store some custom information (tags) in a mp3 file (or even better, in any audio file, but mp3 would be a start).
What would be a good way to do that?
ID3? If yes, in what ID3-Section should that be (it shouldn't be overwritten by other programs). I thought of the "comment" section, but it is overwritten quite frequently, I think.
Is there an easy way to store information to any audio file?
UPDATE:
I decided to store the information into a custom ID3 Tag (with my own name) via the MyID3 library :)
It depends: If you want to use this custom information only for your own collection, you can store it to whatever tag you like. If you hope that your custom information can be read by (nearly) all popular music management tools, I suggest that you store it to the defined tags according the ID3v2.3 standard.
If your custom information doesn't fit into one of this tags, lets assume an example like: "eye color of the lead singer", you could make your own private tag. This is noted in 4.28 private frame with the description:
This frame is used to contain information from a software producer that its program uses and does not fit into the other frames.

Generating an outgoing call in asterisk

I am using asterisk 11.9.0 and i want to generate an outgoing call.I found that for outgoing i have to make a .call file and place it in a var/spool/asterisk/outgoing.I am following the link below
http://the-asterisk-book.com/1.6/call-file.html#call-file-parameter
my code is same as given in the above link,the above example uses only single fixed number to call.
My problem is that
i have to generate an outgoing to a number fetched from database(outgoing to new number everytime),so how to write the code of .call file for multiple numbers outgoing and how to pass these numbers fetched from database to .call file from my extensions.conf
Is there any way to do that.
I am new to asterisk.
Any help would be appreciated.
You can use vicidial.org software to do that things.
Note, it is very bad idea do outboudn dialler-like app in asterisk without understanding asterisk logic and very-hi skills in programming/database.
For more info you also can use this page
http://www.voip-info.org/wiki/view/Asterisk+auto-dial+out
Might be easier using WombatDialer as it has a plain API where you can tell it what you want it to do and it will take care of the rest. We have a plain set up for outbound and it took maybe a couple of days from zero to what we have now. ViciDial would have been overkill.
On why rolling your own is not a great idea, the Wombat manual is quite clear: http://manuals.loway.ch/WD_UserManual-chunked/ch01.html#_why_was_wombatdialer_created
You could also use the AMI (Asterisk Manager Interface), would be easier to program with a deamon running in the back to control what gets dialed and the responses to those dials. Mora info here https://wiki.asterisk.org/wiki/pages/viewpage.action?pageId=4817239.

libxml2 writer differences

The bulk of the examples I can find for libxml2 are all about loading/parsing XML files. But I'm only interested in writing them; the code will never have to parse any files. There is an example using different writers, where it shows how to use the file, memory, DOM and tree models.
Looking through the code, I don't see any significant differences between them when it comes to writing. How does one decide which is better to use? (In other words, in what cases is one better than the others?)
The differences between the 4 functions you specify are minimal, it's all about where the contents go. As Alex mentioned, if memory is a concern, using xmlNewTextWriterFilename has the advantage of not needing to hold the result in memory.
The xmlWriter API, to which all the methods you mentioned belong, is one of the APIs offered. The other of note is the tree API. xmlWriter is more like calling write() to print to a file, and the tree is more like building nested structs in memory.
The tree-based versions can be good if your data is constructed in a non-linear fasion, going back and adding/changing things based on later information, etc. This would require some workarounds/caching with the streaming xmlWriter interface, as you can't change things once they've been output. The in-memory tree, however, can be fully tweaked until the instant it's serialized.
The tree API has the downside of the fact it has to keep the entire thing im memory; the rule of thumb is the memory requirements for a parsed tree is rougly 4x the size of serialized xml file.
My decision is usually dependent on whether I expect to create large documents. If not, I use the if the tree api, as the flexibility will be there if I want it. If I know efficiency will be a concern or I'll be working with large stuff, the streaming xmlWriter is the way to go.
tree API examples can be found here: http://xmlsoft.org/examples/index.html#Tree
If you're on a device with limited memory, you probably don't want to use DOM or memory-based approaches. In that case, you probably want to write out the file as you iterate through the data structure you want to write to XML.

Is libxml2 a DOM parser or a Serial Parser?

I made a wrapper for some basic things in libxml2, stuff like grabbing element content, stepping into children nodes etc.
My super has just asked me to make sure I'm parsing the XML file serially and not loading the entire DOM into memory.
I'm pretty sure the I'm doing it serially, but I couldn't find any documentation on parsing one way or the other.
Any help is appreciated, thanks!
libxml2 can operate in either mode. It just depends how your code uses it. You can either parse the full file into a DOM, or use Sax callbacks to parse serially. What does your parsing code look like?
There are two different APIs you can use.
xmlTextReader is a streaming reader that you'd want to use, calling xmlTextReaderRead() repleatedly to advance the parser through the file.
http://xmlsoft.org/xmlreader.html
If you're working with xmlDocPtr/xmlNodePtr objects returned by things like xmlParseFile, then that's the tree-based DOM API.
http://xmlsoft.org/examples/index.html#tree1.c

Java Project Modules - use InputStream/OutputStream or .tmpFile/byte[]

I found myself passing InputStream/OutputStream objects around my application modules.
I'm wondering if it's better to - save the content to disk and pass something like a Resource between the various methods calls - use a byte[] array instead of having to deal with streams everytime.
What's your approach in these situations?Thanks
Edit:
I've a Controller that receives a file uploaded by the user. I've an utility module that provides some functionality to render a file.
utilityMethod(InputStream is, OutputStream os)
The file in InputStream is the one uploaded by the user. os is the stream associated with the response. I'm wondering if it's better to have the utility method to save the generated file in a .tmp file and return the file path, or a byte[], etc. and have the controller to deal with the outputStream directly.
I try to keep as much in RAM as possible (mostly because of performance reasons and RAM is cheap). So I'm using a FileBackedBuffer to "save" data of unknown size. It has a limit. When less than limit bytes are written to it, it will keep them in an internal buffer. If more data is written, I'll create the actual file. This class has methods to get an InputStream and an OutputStream from it, so the using code isn't bothered with the petty details.
The answer actually depends on the context of the problem, which we dont know.
So, imagining the most generic case, I would create two abstractions. The first abstraction would take InputStream/OutputStream as parameters, whereas the other would take byte[].
The one that takes streams can read and pass the data to the byte[] implementation. So now your users can use both the stream abstraction and byte[] abstraction based on thier needs/comfort.

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