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• opus : add a native Opus encoder

  11 février 2017, par Rostislav Pehlivanov

  opus : add a native Opus encoder
  This marks the first time anyone has written an Opus encoder without
  
  using any libopus code. The aim of the encoder is to prove how far
  
  the format can go by writing the craziest encoder for it.
  Right now the encoder’s basic, it only supports CBR encoding, however
  
  internally every single feature the CELT layer has is implemented
  
  (except the pitch pre-filter which needs to work well with the rest of
  
  whatever gets implemented). Psychoacoustic and rate control systems are
  
  under development.
  The encoder takes in frames of 120 samples and depending on the value of
  
  opus_delay the plan is to use the extra buffered frames as lookahead.
  
  Right now the encoder will pick the nearest largest legal frame size and
  
  won’t use the lookahead, but that’ll change once there’s a
  
  psychoacoustic system.
  Even though its a pretty basic encoder its already outperforming
  
  any other native encoder FFmpeg has by a huge amount.
  The PVQ search algorithm is faster and more accurate than libopus’s
  
  algorithm so the encoder’s performance is close to that of libopus
  
  at zero complexity (libopus has more SIMD).
  
  The algorithm might be ported to libopus or other codecs using PVQ in
  
  the future.
  The encoder still has a few minor bugs, like desyncs at ultra low
  
  bitrates (below 9kbps with 20ms frames).
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] configure
  • [DH] libavcodec/Makefile
  • [DH] libavcodec/allcodecs.c
  • [DH] libavcodec/opus_celt.h
  • [DH] libavcodec/opus_pvq.c
  • [DH] libavcodec/opus_pvq.h
  • [DH] libavcodec/opusenc.c

• Re-solving My Search Engine Problem

  28 juillet 2012, par Multimedia Mike — General, swish-e

  14 years ago, I created a web database of 8-bit Nintendo Entertainment System games. To make it useful, I developed a very primitive search feature.

  A few months ago, I decided to create a web database of video game music. To make it useful, I knew it would need to have a search feature. I realized I needed to solve the exact same problem again.

  Requirements
  The last time I solved this problem, I came up with an excruciatingly naïve idea. Hey, it worked. I really didn’t want to deploy the same solution again because it felt so silly the first time. Surely there are many better ways to solve it now ? Many different workable software solutions that do all the hard work for me ?

  The first time I attacked this, it was 1998 and hosting resources were scarce. On my primary web host I was able to put static HTML pages, perhaps with server side includes. The web host also offered dynamic scripting capabilities via something called htmlscript (a.k.a. MIVA Script). I had a secondary web host in my ISP which allowed me to host conventional CGI scripts on a Unix host, so that’s where I hosted the search function (Perl CGI script accessing a key/value data store file).

  Nowadays, sky’s the limit. Any type of technology you want to deploy should be tractable. Still, a key requirement was that I didn’t want to pay for additional hosting resources for this silly little side project. That leaves me with options that my current shared web hosting plan allows, which includes such advanced features as PHP, Perl and Python scripts. I can also access MySQL.

  Candidates
  There are a lot of mature software packages out there which can index and search data and be plugged into a website. But a lot of them would be unworkable on my web hosting plan due to language or library package limitations. Further, a lot of them feel like overkill. At the most basic level, all I really want to do is map a series of video game titles to URLs in a website.

  Based on my research, Lucene seems to hold a fair amount of mindshare as an open source indexing and search solution. But I was unsure of my ability to run it on my hosting plan. I think MySQL does some kind of full text search, so I could have probably made a solution around that. Again, it just feels like way more power than I need for this project.

  I used Swish-e once about 3 years ago for a little project. I wasn’t confident of my ability to run that on my server either. It has a Perl API but it requires custom modules.

  My quest for a search solution grew deep enough that I started perusing a textbook on information retrieval techniques in preparation for possibly writing my own solution from scratch. However, in doing so, I figured out how I might subvert an existing solution to do what I want.

  Back to Swish-e
  Again, all I wanted to do was pull data out of a database and map that data to a URL in a website. Reading the Swish-e documentation, I learned that the software supports a mode specifically tailored for this. Rather than asking Swish-e to index a series of document files living on disk, you can specify a script for Swish-e to run and the script will generate what appears to be a set of phantom documents for Swish-e to index.
  

  When I ’add’ a game music file to the game music website, I have a scripts that scrape the metadata (game title, system, song titles, composers, company, copyright, the original file name on disk, even the ripper/dumper who extracted the chiptune in the first place) and store it all in an SQLite database. When it’s time to update the database, another script systematically generates a series of pseudo-documents that spell out the metadata for each game and prefix each document with a path name. Searching for a term in the index returns a lists of paths that contain the search term. Thus, it makes sense for that path to be a site URL.

  But what about a web script which can search this Swish-e index ? That’s when I noticed Swish-e’s C API and came up with a crazy idea : Write the CGI script directly in C. It feels like sheer madness (or at least the height of software insecurity) to write a CGI script directly in C in this day and age. But it works (with the help of cgic for input processing), just as long as I statically link the search script with libswish-e.a (and libz.a). The web host is an x86 machine, after all.

  I’m not proud of what I did here— I’m proud of how little I had to do here. The searching CGI script is all of about 30 lines of C code. The one annoyance I experienced while writing it is that I had to consult the Swish-e source code to learn how to get my search results (the "swishdocpath" key — or any other key — for SwishResultPropertyStr() is not documented). Also, the C program just does the simplest job possible, only querying the term in the index and returning the results in plaintext, in order of relevance, to the client-side JavaScript code which requested them. JavaScript gets the job of sorting and grouping the results for presentation.

  Tuning the Search
  Almost immediately, I noticed that the search engine could not find one of my favorite SNES games, U.N. Squadron. That’s because all of its associated metadata names Area 88, the game’s original title. Thus, I had to modify the metadata database to allow attaching somewhat free-form tags to games in order to compensate. In this case, an alias title would show up in the game’s pseudo-document.

  Roman numerals are still a thorn in my side, just as they were 14 years ago in my original iteration. I dealt with it back then by converting all numbers to Roman numerals during the index and searching processes. I’m not willing to do that for this case and I’m still looking for a good solution.

  Another annoying problem deals with Mega Man, a popular franchise. The proper spelling is 2 words but it’s common for people to mash it into one word, Megaman (see also : Spider-Man, Spiderman, Spider Man). The index doesn’t gracefully deal with that and I have some hacks in place to cope for the time being.

  Positive Results
  I’m pleased with the results so far, and so are the users I have heard from. I know one user expressed amazement that a search for Castlevania turned up Akumajou Densetsu, the Japanese version of Castlevania III : Dracula’s Curse. This didn’t surprise me because I manually added a hint for that mapping. (BTW, if you are a fan of Castlevania III, definitely check out the Akumajou Densetsu soundtrack which has an upgraded version of the same soundtrack using special audio channels.)

  I was a little more surprised when a user announced that searching for ’probotector’ correctly turned up Contra : Hard Corps. I looked into why this was. It turns out that the original chiptune filename was extremely descriptive : "Contra - Hard Corps [Probotector] (1994-08-08)(Konami)". The filenames themselves often carry a bunch of useful metadata which is why it’s important to index those as well.

  And of course, many rippers, dumpers, and taggers have labored for over a decade to lovingly tag these songs with as much composer information as possible, which all gets indexed. The search engine gets a lot of compliments for its ability to find many songs written by favorite composers.

• No such file or directory Error with FFMPEG + CarrierWave screenshot method

  10 juillet 2013, par dodgerogers747

  I am using AWS CORS to upload videos to my site, all of which works as planned.

  I have the following model method which runs as an after_create callback (for speed) to take a screenshot from the video file on AWS. I plan to move this out into a delayed job but I don't think this will solve this particular issue. Please advise if mistaken.

  I use FFMPEG to take a screenshot from the AWS self.file location, I then send the file to CarrierWave by saving the file to self.screenshot where it is uploaded to AWS.

  Approx. 50% of the time it errors out with Errno::ENOENT - No such file or directory for the location of the screenshot image.

  How can I rectify my code to remove this error and how come it only occurs around 50% of the time ? If anyone needs more code just shout.

  video.rb

  after_create :take_screenshot
  
  
  
  mount_uploader :screenshot, ImageUploader
  
  
  
    def take_screenshot
  
      location = "#{Rails.root}/public/uploads/tmp/screenshots/#{unique}_#{File.basename(file)}.jpg"
  
      system `ffmpeg #{log_level} -i #{self.file} -ss 00:00:0#{time_frame} -vframes 1 #{location}`
  
      logger.debug "Trying to take screenshot from #{self.file}"
  
      #pass the actual file to CarrierWave to handle the image upload
  
      self.screenshot = File.open(location)
  
      self.save
  
      logger.debug "Deleting tmp file: #{location}: #{File.delete(location)}" if self.screenshot.present?
  
    end
  
  
  
  def unique
  
      (0..6).map{(65+rand(26)).chr}.join
  
    end
  
  
  
  def log_level
  
      "-loglevel panic"
  
    end
  
  
  
    def time_frame
  
      rand(0..3)
  
    end

  Stack trace :

  Started POST "/videos" for 127.0.0.1 at 2013-07-10 03:58:49 +0800
  
  Processing by VideosController#create as JS
  
    Parameters: {"utf8"=>"✓", "authenticity_token"=>"6M1Ia+Ag2E3HVKH2PO/p7jewxSpMPdWeVHGA933Bzjw=", "video"=>{"file"=>"http://bucketname.s3.amazonaws.com/uploads/video/file/671a87fb-91de-4eaf-a38a-1b25c51798e5/Good_7iron.m4v"}}
  
    User Load (0.3ms)  SELECT `users`.* FROM `users` WHERE `users`.`id` = 9 LIMIT 1
  
     (0.1ms)  BEGIN
  
    SQL (0.2ms)  INSERT INTO `videos` (`created_at`, `file`, `question_id`, `screenshot`, `updated_at`, `user_id`) VALUES ('2013-07-09 19:58:49', 'http://bucketname.s3.amazonaws.com/uploads/video/file/671a87fb-91de-4eaf-a38a-1b25c51798e5/Good_7iron.m4v', NULL, NULL, '2013-07-09 19:58:49', 9)
  
  Trying to take screenshot from http://bucketname.s3.amazonaws.com/uploads/video/file/671a87fb-91de-4eaf-a38a-1b25c51798e5/Good_7iron.m4v
  
     (0.8ms)  ROLLBACK
  
  Completed 500 Internal Server Error in 3550ms
  
  
  
  Errno::ENOENT - No such file or directory - /Users/me/rails/project/public/uploads/tmp/screenshots/WCACLIC_Good_7iron.m4v.jpg:
  
    app/models/video.rb:24:in `initialize'
  
    app/models/video.rb:24:in `open'
  
    app/models/video.rb:24:in `take_screenshot'