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• How to do Slow Motion video in IOS

  4 mai 2022, par 2vision2

  I have to do "slow motion" in a video file along with audio, in-between some frames and need to store the ramped video as a new video.

  



  Ref : http://www.youtube.com/watch?v=BJ3_xMGzauk (watch from 0 to 10s)

  



  From my analysis, I've found that AVFoundation framework can be helpful.

  



  Ref :
http://developer.apple.com/library/ios/#documentation/AudioVideo/Conceptual/AVFoundationPG/Articles/00_Introduction.html

  



  Copy and pasted from the above link :

  



  "
Editing
AV Foundation uses compositions to create new assets from existing pieces of media (typically, one or more video and audio tracks). You use a mutable composition to add and remove tracks, and adjust their temporal orderings. You can also set the relative volumes and ramping of audio tracks ; and set the opacity, and opacity ramps, of video tracks. A composition is an assemblage of pieces of media held in memory. When you export a composition using an export session, it's collapsed to a file.
On iOS 4.1 and later, you can also create an asset from media such as sample buffers or still images using an asset writer.

  



  "

  



  Questions :
Can I do " slow motion " the video/audio file using the AVFoundation framework ? Or Is there any other package available ? If i want to handle audio and video separately, please guide me how to do ?

  



  Update : : Code For AV Export Session :

  



   NSArray *paths = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES);
    NSString *outputURL = paths[0];
    NSFileManager *manager = [NSFileManager defaultManager];
    [manager createDirectoryAtPath:outputURL withIntermediateDirectories:YES attributes:nil error:nil];
    outputURL = [outputURL stringByAppendingPathComponent:@"output.mp4"];
    // Remove Existing File
    [manager removeItemAtPath:outputURL error:nil];
    AVAssetExportSession *exportSession = [[AVAssetExportSession alloc] initWithAsset:self.inputAsset presetName:AVAssetExportPresetLowQuality];
    exportSession.outputURL = [NSURL fileURLWithPath:outputURL]; // output path;
    exportSession.outputFileType = AVFileTypeQuickTimeMovie;
    [exportSession exportAsynchronouslyWithCompletionHandler:^(void) {
        if (exportSession.status == AVAssetExportSessionStatusCompleted) {
            [self writeVideoToPhotoLibrary:[NSURL fileURLWithPath:outputURL]];
            ALAssetsLibrary *library = [[ALAssetsLibrary alloc] init];
            [library writeVideoAtPathToSavedPhotosAlbum:[NSURL fileURLWithPath:outputURL] completionBlock:^(NSURL *assetURL, NSError *error){
                if (error) {
                    NSLog(@"Video could not be saved");
                }
            }];
        } else {
            NSLog(@"error: %@", [exportSession error]);
        }
    }];


  


• Tracking User Acquisition and Social Media Activity with Piwik

  25 avril 2017, par Florian Hieß — Community

  Being able to monitor user acquisition and social media activity is essential for determining whether the outcome of your campaigns is in line with the business objectives. Determining the source of each website visit that gets you closer to your business goals enables you to focus your efforts in the directions that are worth it. In this article you will learn why it is important to identify your traffic sources and how you can track user acquisition with Piwik Analytics.

  Why Is It Important to Identify Traffic Sources on Your Website ?

  Since brands nowadays use multiple channels for promotion and advertising, identifying the touch points and traffic sources of a lead or customer seems to become more and more difficult. And yet, this channel multiplication is what makes the source of a purchase more important. Once you identify the traffic origin and how each source is performing you are able to increase your efforts on the best performers, both in terms of human resources and monetary investments, to attract more leads or customers in these marketing channels.

  The default referrer types are defined by :

  • Search engine
  • Direct traffic
  • Websites and
  • Campaigns

  But consider that within the “Campaigns” type, each of the following referrers is a possible traffic source for your website and can be tracked with the Piwik URL builder :

  • Google AdWords
  • Display Ads, Banners
  • Links in Newsletters, Emailing
  • Affiliate links
  • Tweets
  • Facebook Ads

  Measure your performance and conversion

  With so many options, wouldn’t you like to know which one of them worked best ? To rate channels based on their performance, you first need to establish conversion goals and attribution.

  A conversion can be anything from sign-ups or downloads to leads, registered users and even paying customers. Define conversions based on what you want people to do once they’ve landed on your website.

  

  You need to define each conversion type in the Piwik dashboard, so that the analytics platform knows what to track. As far as attribution goes, Piwik by default links the conversion and attributes to the last seen (non-direct) referrer. You are able to change that to the first referrer in the attribution line by following the instructions in this conversion attribution FAQ.

  Track Your User Acquisition Right with Piwik

  Using the Piwik URL Builder tool, you can tag each URL you promote in your campaigns using relevant keywords. Provided that your URLs are tagged, whenever someone clicks on them, the campaign will be listed as the referrer in the Piwik dashboard. Once you’ve generated trackable URLs, you can include them in your social media posts which could be planned and scheduled using a social media management tool such as Swat.io.

  

  Campaign URLs work wonders for telling which campaign helped you reach your goals faster, more efficiently and so on but they do have a downside. They only work for URLs that you’ve shared. If someone decides to share a link of yours on social media they won’t be tagged beforehands. This is where the Referrers section of Piwik comes in handy, as it acts as a backup for tracking traffic sources. The overview tab features a graph that can help you identify when spikes occurred.

  

  As well as a numerical representation of the main referrer categories for the selected time period.

  

  Switching from Overview to Websites & Social, you can see a graphical representation of the social networks acting as referrers. The visualization can be changed to bar graphs or table, and can be easily exported in various formats for reports.

  

  The websites list features not only the social referrers, but all of the websites generating visits to your website. With Piwik you should not have issues with referrer spam, as the Piwik core team has tackled this problem early on, as detailed in how to stop referrer spam. Our analytics spam blacklist is a public project on GitHub.

  

  Assuming that you’re relying only on Facebook and VK.com for your campaigns, as the above screenshot would suggest, you might want to give paid advertising a try on these two social networks. Paid ads can increase reach and engagement, can get more relevant visitors to your website and can have a snowball effect in a short period of time.

  What Social Networks Can Piwik Track ?

  Piwik’s built-in social network list is quite extensive, as it currently features 70 platforms. The entries range from popular social networks such as Facebook, Twitter and LinkedIn to more obscure ones such as Renren. However, this list is not available by default, and to see it or alter it, you would need a third-party plugin.

  How Does the Referrers Manager Plugin for Piwik Work ?

  The Referrers Manager plugin for Piwik provides access to the list of search engines and social networks that this analytics platform can handle by default. The simple plugin can come in handy when sorting out referrers. First of all, it displays a list of all search engines and social networks that Piwik can handle by default. Secondly, it enables users to disable/enable the platform’s default social network list. And using Referrers Manager, you can add custom engines or social networks to the referrers list in case they’re not already available.

  

  Conclusions

  Piwik is a very capable analytics platform as it is, but combined with third-party plugins such as Referrers Manager, it can provide even better insights on where your visitors are coming from. Remember to correlate the referrers with goals in order to determine which website or social network performs best in your context. And don’t forget to assign a monetary revenue value to each goal, in order to determine your social media ROI with greater accuracy.

• How does one correctly avoid the avcodec_alloc_context3 leak from avformat_new_stream ?

  14 avril 2017, par Tom Seddon

  This maddening thread describes the problem I’m having : a memory leak on shutdown due to some stuff allocated when avformat_new_stream is called.

  Here’s the valgrind stack trace from the leak :

  • 1,447 (1,440 direct, 7 indirect) bytes in 1 blocks are definitely lost in loss record 2 of 4
  • at 0x4C2FFC6 : memalign (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
  • by 0x4C300D1 : posix_memalign (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
  • by 0x690DEFF : av_malloc (mem.c:87)
  • by 0x690E09D : av_mallocz (mem.c:224)
  • by 0x533D28A : init_context_defaults (options.c:128)
  • by 0x533D325 : avcodec_alloc_context3 (options.c:164)
  • by 0x663D09E : avformat_new_stream (utils.c:4384)
  • by 0x4204B6 : main (test_ffmpeg.cpp:918)

  So clearly the problem is that when a AVFormatContext’s stream’s codec context’s priv_data field is somehow not being freed.

  My code frees the AVFormatContext with avformat_free_context. This calls ff_free_stream, which calls free_stream, which frees a few of the stream’s codec context fields itself - but not the priv_data field !

  Compared and contrast with the corresponding code in avcodec_close.

  The suggested solution to the problem from the thread : "close the codec firstly before calling av_format_free_context". Presumably this refers to calling avcodec_free_context ? - but I’m already doing this ! Roughly following the structure in the muxing example, I have an encoder context created by my code, that’s used to track the uncompressed input data. Then there’s another encoder context created internally by avformat_new_stream (as above), which is used internally by FFmpeg. I close the former, because it was opened using avcodec_open2, but I don’t close the latter, because it wasn’t. I am following the maddening thread’s advice, and yet here I am.

  Furthermore, reading between the lines, using avcodec_free_context to free the AVStream’s codec context is no good anyway, because when doing this (a) AVStream’s codec field is deprecated, so this gives a bunch of warnings, and (b) there are no NULL checks in free_stream, so this crashes at runtime.

  What I have done for now is drag in the appropriate bit of code from avcodec_close, and put it in my own code just ahead of the call to avformat_free_context :

  #ifdef __GNUC__
  
  #pragma GCC diagnostic push
  
  #pragma GCC diagnostic ignored "-Wdeprecated-declarations"
  
  #endif
  
      for(unsigned i=0;inb_streams;++i) {
  
          AVStream *st=avf_context->streams[i];
  
  
  
          if(st->codec->priv_data&&
  
             st->codec->codec&&
  
             st->codec->codec->priv_class)
  
          {
  
              av_opt_free(st->codec->priv_data);
  
          }
  
  
  
          av_freep(&st->codec->priv_data);
  
      }
  
  #ifdef __GNUC__
  
  #pragma GCC diagnostic pop
  
  #endif

  So that fixes the leak, and it’s clearly (to my eyes) a bug, and I need to file a bug report or something.

  However the corresponding bug report is marked as fixed and closed... along with a link back to the maddening thread, and no further explanation. (This is why it is maddening !) So maybe I’m just using FFmpeg wrongly ?

  Can anybody confirm whether this is actually a bug in FFmpeg or not ?

  If it isn’t a bug, what’s the right sequence of calls to make ?

  (I’m using FFmpeg built locally from commit 03eb0515c12637dbd20c2e3ca8503d7b47cf583a. I had similar-looking problems with the one you get from the Ubuntu 16 package manager, which prompted me to build it myself with symbols and so on.)