I working on metadata of various file formats,extraction of these metadata and changing these metadata. I found some java libraries for these but I want to implement these metadata extractors in C.
Please somebody give me some advice for how to proceed for writing these extractors. I would be really happy if somebody can provide me good links regarding these also
I would suggest you take a look at libavformat, which is part of ffmpeg. It's a C library that parses essentially all important audio and video containers.
Here's the documentation: http://www.ffmpeg.org/documentation.html
Related
My question is basically that I am new to this framework and I am looking at pointers to how to work with non-file sources in media foundation since the documentation in this front seems lacking in my mind. Below is some info on what I am doing and what approach I am working with right now but I have no idea if it is the correct way to use the framework.
I am currently trying to use Microsoft Media Foundation to decode audio that I'm getting over Bluetooth and then send it along as PCM audio. When looking at the documentation for ms media foundation it seems that almost all examples assume the source is a file.
Looking at the tutorial for decoding audio for example they use MFCreateSourceReaderFromURL, which I cannot use since my source is not a file.
As I wanted to follow the tutorial and change as little as possible Im thinking that I need only change how I create the source reader and the rest of the process would be the same. I looked at the other SourceReaders available and MFCreateSourceReaderFromByteStream sounds about right for my purposes.
Is there a chance that I only need to create a bytestream and continuously fill it with data that I get over the air as we go and the media source created by MFCreateSourceReaderFromByteStream handle this well? Or do I need to create a custom media source and do more manual work at the lower parts of the API to get something like this to work?
Or maybe a source reader is the wrong approach altogether when the source is not a file? In the main page about Source Reader here they have the following picture:
And this picture shows the media source within the source reader pointing to a source file only, is this a real limitation or simply and example?
Im writing this in plain c, but pointing to c++ documentation or examples is fine as its usually pretty straightforward to translate c++ to c and there seems to be no documentation for c anyways.
Edit:
Im adding a image on what kind of data Im getting, the red area being the chunks of data I refer to in comments below Source.
Non-file source is not a accurate description. Does it have a file structure, just not a file? Structured differently? Raw stream?
If you look at samples with source reader, they assume presence and usage of stream handler capable to parse incoming stream into elementary streams with known type and properties. Then you or Media Foundation could apply decoder or otherwise transform the data.
As you specified that the data come "in chunks", most likely that you are interested in an alternate option to use AAC Decoder explicitly. You can create an instance of it, initialize input and output types, then feed it with compressed audio and pull decoded PCM on the output. The decoder has MFT interface.
I'm trying to make a server that receives RTP/H264 video streams from android clients and stores these to file.
Currently I'm using VLC in the server, which works well. However, I am worried that VLC is a heavyweight solution that may not scale well. As I'm not actually playing the video, only saving it to file, I thought there must a be a more efficient solution.
Currently I'm planning on using an Amazon ec2 instances, so the goal is to serve as many clients as possible per instance.
I'm flexible (willing to learn) on the language side, I'd like to choose the right language for the job.
So, does anyone know of a good, scalable way to store these streams to files?
Thanks in advance!
EDIT
FFmpeg or libav look promising. Looking into them now.
Basically you need an library that supports rtp stack server side, so you can extract the payload and just append to a file as it comes. ffmpeg is a great choice, and it does have rtp stack and it also it can generate containers(MP4,...) for you as well; if needed. Actually VLC uses ffmpeg's libav library under the hood.
When I was looking at the www.bing.com/maps html source file I came across some
strange "streetsidePrefetchFileUrls" URLs to .xap.png archives:
For exmaple:
hxxp://c0.ecn.catalogservice.virtualearth.net/cs/dc/pf/Xaps/bcbc3954e568c46cf8c3cc00737da32c_Microsoft.Maps.Framework.xap.png
This file has a PNG Header and contains an IDAT chunk. The IDAT chunk doesn't contain pixel data but a (corrupt) PKZIP archive with Microsoft Maps DLLs inside.
Does anybody know why Microsoft uses PNG as a container for xap Archives?
I've tried to unpack that archive with unzip and 7z. They all detect the ZIP-Archive inside the PNG but abort unpacking with an error.
Yes I noticed this they changed to this kind of protection just before the map app api came out of Beta. I presume it is their way of providing some protection for xap code from 3rd party developers, we have tried lots of ways to decrypt these without any luck but the code for it must be in the initial silverlight code so with a lot of decompiling you could probably find it
Many of the Bing Maps App's available on http://bing.com/maps contain proprietary algorithms and code. The png encoding is there to help prevent people from decrypting the XAP files and decompiling them. That said, if there is something you are trying to figure out how to do then try asking that question instead.
I used Sphinx4 for some time which really fits my needs. I load a recognizer, pass the audio data to it and use the recognized String in my application.
Right now I'm working on a C application (C++ is unfortunately not an option) where I need something similar and thought that I could use Sphinx3 which is written in C.
The problem is that I don't really know how it is used inside an application and there is no "Hello World"-example as Sphinx4 provides it.
I already compiled and installed sphinxbase and sphinx3 and now I can include the sphinx header files in my application.
Now to my questions:
Is there a "simple" and well documented example application that uses sphinx3 from a C environment?
How can I load up the sphinx3 engine and call a recognizer with my binary audio data?
OR: Do I need to start an application like "sphinx3_decode" and call it from my own application? If so, is there an example application for that?
Thank you in advance!
Best regards,
Robert
It's not recommended to use Sphinx3. From the website:
Sphinx-3 is CMU’s large vocabulary speech recognition system. It’s
older C based decoder that we continue to maintain. It’s planned to
make it obsolete in the future, it’s still most accurate decoder for
large vocabulary tasks. We are using it as a baseline to check the
recognizer accuracy. This decoder is only intended for researchers who
want to evaluate bleeding edge methods in ASR like tree search method.
If you need to use a decoder you should use pocketsphinx. You can find the tutorial and the API documentation on the website
http://cmusphinx.sourceforge.net/wiki/tutorialpocketsphinx
http://cmusphinx.sourceforge.net/api/pocketsphinx/pocketsphinx_8h.html
I Recently worked on an Intregated Project on Punjabi Language.
Here are some steps that we used...
First we recorded the punjabi audio data in a vaccumed room in 16000 hz sample rate.
Then we took the recorded data and segmented it using Praat Software into small wav and raw files of 2 to 30 sec and saved them in a folder named train.
Then we took a system having Linux ie. Ubuntu and installed the required plug in like autoconfig, automake etc and untarred Sphinx 3 along with 4 packages that are cmuclmtk, pocketsphinx, sphinxbase, sphinxtrain.
Then according to the small wav files we made many files like transcription, dic, phone, filler, file id, ccs etc.
Then we opened the terminal and typed –"sphinx_fe” to check the whether the sphinx is functional or not.
Then we created an folder named “man” and then in terminal wrote its path.
Then we run the command- “sphinxtrain –t man setup”. By running this command an folder named “etc” will be formed in “man” folder containing files “feat_paramas” & ”config”.
Changes were made in the in the config file according to our data.
Then we moved all the files that we created before ie. transcription, dic in the etc folder in that is located in man folder.
Then we placed ‘lang1.sh” script in etc folder and remaining 4 scripts in man folder.
Then we opened the path for etc folder in terminal and run command- “lang1.sh”
Then we run series of commands in terminal – “mfcgen2.sh” then “verify3.sh” then “hmm4.sh” and at last “end-test.sh” to get the final result.
Rest if you have worked on Sphinx 4 then you may know about the files that are mentioned above in the steps. I hope this helps you.
I would like to write a custom GlusterFS Translator for file encryption with AES. Besides this rather rare description:
http://europe.gluster.org/community/documentation/index.php/GlusterFS_Contributors_FAQ, is there any other documentation on writing a custom Translator?
Maybe HekaFS is what you need, it already has a encryption translator.
You can find some dated documentation in the hacker-guide directory of the source repository:
http://git.gluster.com/?p=glusterfs.git;a=tree;f=doc/hacker-guide;hb=HEAD
hacker-guide.tex should be a good place to start.
There is a detailed talk on this topic from #oscon12, which is being recorded today, from RedHat ,also suggest you download the slides
Here's a link to the presentation slides