Recherche avancée

Sur d’autres sites (12494)

• Revision 31957 : légère amélioration ... Un peu de documentation dans le code également

  7 octobre 2009, par kent1@… — Log

  légère amélioration ...
  Un peu de documentation dans le code également

• Inside WebM Technology : The VP8 Alternate Reference Frame

  15 juin 2010, par noreply@blogger.com (John Luther) — inside webm, vp8

  Since the WebM project was open-sourced just a week ago, we’ve seen blog posts and articles about its capabilities. As an open project, we welcome technical scrutiny and contributions that improve the codec. We know from our extensive testing that VP8 can match or exceed other leading codecs, but to get the best results, it helps to understand more about how the codec works. In this first of a series of blog posts, I’ll explain some of the fundamental techniques in VP8, along with examples and metrics.

  The alternative reference frame is one of the most exciting quality innovations in VP8. Let’s delve into how VP8 uses these frames to improve prediction and thereby overall video quality.

  Alternate Reference Frames in VP8

  VP8 uses three types of reference frames for inter prediction : the last frame, a "golden" frame (one frame worth of decompressed data from the arbitrarily distant past) and an alternate reference frame. Overall, this design has a much smaller memory footprint on both encoders and decoders than designs with many more reference frames. In video compression, it is very rare for more than three reference frames to provide significant quality benefit, but the undesirable increase in memory footprint from the extra frames is substantial.

  Unlike other types of reference frames used in video compression, which are displayed to the user by the decoder, the VP8 alternate reference frame is decoded normally but is never shown to the user. It is used solely as a reference to improve inter prediction for other coded frames. Because alternate reference frames are not displayed, VP8 encoders can use them to transmit any data that are helpful to compression. For example, a VP8 encoder can construct one alternate reference frame from multiple source frames, or it can create an alternate reference frame using different macroblocks from hundreds of different video frames.

  The current VP8 implementation enables two different types of usage for the alternate reference frame : noise-reduced prediction and past/future directional prediction.

  Noise-Reduced Prediction

  The alternate reference frame is transmitted and decoded similar to other frames, hence its usage does not add extra computation in decoding. The VP8 encoder however is free to use more sophisticated processing to create them in off-line encoding. One application of the alternate reference frame is for noise-reduced prediction. In this application, the VP8 encoder uses multiple input source frames to construct one reference frame through temporal or spatial noise filtering. This "noise-free" alternate reference frame is then used to improve prediction for encoding subsequent frames.

  You can make use of this feature by setting ARNR parameters in VP8 encoding, where ARNR stands for "Alternate Reference Noise Reduction." A sample two-pass encoding setting with the parameters :

  --arnr-maxframes=5 --arnr-strength=3

  enables the encoder to use "5" consecutive input source frames to produce one alternate reference frame using a filtering strength of "3". Here is an example showing the quality benefit of using this experimental "ARNR" feature on the standard test clip "Hall Monitor." (Each line on the graph represents the quality of an encoded stream on a given clip at multiple datarates. The higher points on the Y axis (PSNR) indicates the stream with the better quality.)

  
  

  The only difference between the two curves in the graph is that VP8_ARNR was produced by encodings with ARNR parameters and VP8_NO_ARNR was not. As we can see from the graph, noise reduced prediction is very helpful to compression quality when encoding noisy sources. We’ve just started to explore this idea but have already seen strong improvements on noisy input clips similar to this "Hall Monitor." We feel there’s a lot more we can do in this area.

  Improving Prediction without B Frames

  The lack of B frames in VP8 has sparked some discussion about its ability to achieve competitive compression efficiency. VP8 encoders, however, can make intelligent use of the golden reference and the alternate reference frames to compensate for this. The VP8 encoder can choose to transmit an alternate reference frame similar to a "future" frame, and encoding of subsequent frames can make use of information from the past (last frame and golden frame) and from the future (alternate reference frame). Effectively, this helps the encoder to achieve results similar to bidirectional (B frame) prediction without requiring frame reordering in the decoder. Running in two-pass encoding mode, compression can be improved in the VP8 encoder by using encoding parameters that enable lagged encoding and automatic placement of alternate reference frames :

  --auto-alt-ref=1 --lag-in-frames=16

  Used this way, the VP8 encoder can achieve improved prediction and compression efficiency without increasing the decoder’s complexity :

  
  

  In the video compression community, "Mobile and calendar" is known as a clip that benefits significantly from the usage of B frames. The graph above illustrates that the use of alternate reference frame benefits VP8 significantly without using B frames.

  Keep an eye on this blog for more posts about VP8 encoding. You can find more information on above encoding parameters or other detailed instructions to use with our VP8 encoders on our site, or join our discussion list.

  Yaowu Xu, Ph.D. is a codec engineer at Google.

  

• 10 Proven Ways Heatmap Software Improves Website Conversions

  20 septembre 2021, par Ben Erskine — Analytics Tips, Plugins, Heatmap
  

  Heatmap software is critical in improving website conversions. Why ? Because it provides customer-centric insights. 

  In the online market, businesses that are customer-centric are 60% more profitable than businesses that are not.

  Using heatmaps to track factors such as usability, compare A/B landing pages and content engagement across channels optimises online conversions by addressing issues faced by real users. 

  How heatmaps benefit your customers

  Customer experience is one of the most important factors in business success. 

  Website heatmap software like Matomo offers unique insights into customer behaviour that is then used to improve their experience, usability and engagement. 

  Data analysis captures information on how many people complete a sales funnel or bounce from a website. Behavioural analytics like heatmaps can show you why they bounce.

  This benefits your customers (and therefore your bottom line) because it puts the focus on them and their needs.

  10 ways heatmap software helps increase website conversions

  #1. Improve UX/Usability 

  Heatmap analytics improve usability by identifying where you are losing customers on your website.

  Forrester research indicates that improving user experience can improve conversions by up to 400%, and on average every $1 spent on UX has a return of $100. 

  For example, you may have a CTA button but customers never click it to reach the payment page. 

  Heatmaps show you how customers interact with your website naturally so that you can adjust it according to their needs.

  Using heatmap analytics to improve usability boosts conversions because it improves customer experiences. 88% of online consumers say that they wouldn’t even bother returning to a website after a bad experience. 

  #2. Website design and content structure 

  Another way that heatmaps can improve conversions is to analyse your website design and content structure. 

  You might be wondering how often a specific ad or a banner was displayed and viewed by your visitors on any of your pages and how often a visitor actually interacted with them. These two parts of the analysis are called content impression and content interaction.

  Ideally, your website elements such as banners, listings, buttons and thumbnails will entice customers to click and find out more. 

  Heatmaps and click maps analyse

  1. How many impressions the content has (e.g. a banner), and
  2. What percent of users that see the content click on it 

  For example, you may have a banner with high impressions but low click-through rates. Tracking content interactions optimises your website by showing which elements or CTAs need more visibility. 

  #3. A/B testing

  Heatmaps provide invaluable data on which landing pages are converting the best. Not only that, but session recordings and heatmap data can show you exactly why one is converting better so that you can replicate the results to increase conversions on other landing pages.

  Tracking heatmap updates on different versions of the same sales page will help confirm creative solutions faster than feedback alone. 

  Ultimately this kind of comparison increases your ROI faster because you are not guessing why some customers are converting and others are not. 

  #4. Conversion Funnel

  Using heatmap software in sales funnels lets you visualise user behaviour at each stage of the conversion process. 

  For example, if many customers are dropping off a payment page, heatmaps can indicate whether it is a usability issue such as pop ups, lack of clarity with payment buttons or something web developers haven’t seen from the back end. 

  These analytics improve conversions by reducing friction in sales funnels as much as possible. 

  #5. Content engagement across channels 

  Optimising websites across all channels is now expected for online businesses. 

  Bad mobile optimisation annoys 48% of online shoppers, and if your web page takes longer than 3 seconds to load, 53% of visitors will simply click away. 

  You can use heatmaps to improve engagement by tracking mouse activity, clicks and scrolling. This helps improve conversions by confirming 

  • How invested a user is in the page 
  • How easy it is to navigate your website and content on different devices 
  • What is your most viewed content and what to push more of 
  • How users generally move through your website on different devices 
  • How clear your messaging is (e.g. high click through rate but low engagement could indicate they aren’t finding what they’re looking for once they click on a CTA)

  #6. Above the fold analysis 

  Although a well-used web development term, above the fold is still one of the most important factors in heatmap analysis. 

  Above the fold analysis gives you insight into a customer’s first impression of a page. 

  An example of above-the-fold heatmaps in action could be a page with a video explanation. Say you have a landing page with a video below the fold that explains why someone should buy and has a CTA button underneath. If there are a lot of page visitors but very few people scrolling below the fold, you can see why hardly any visitors are watching the video or engaging with the CTA button. 

  Insights like this would inform further development such as including important video content above the fold or updating header copy to encourage visitors to scroll down the page more often.

  

  #7. Session recording

  Recording features go hand in hand with heatmap visualisations. Recording features like Session Recording shows the flow of each user’s time on your website. 

  For example, a session recording replays all clicks, mouse movements, scrolls, window resizes, form interactions, and page changes (e.g. when a popup appears).

  #8. Scroll heatmap 

  A scroll heatmap shows the percentage of people that have seen a part of the page. 

  For example, the top of a website page will be the “hottest” in a scroll heatmap, and it naturally gets “colder” further down.

  Tracking this shows whether customers are staying on the page, whether they are only seeing information above the fold, and whether sales pages are engaging. 

  It is an effective strategy for improving sales pages because it shows where customers are losing interest and which elements receive the most engagement.

  

  #9. Records clicks 

  With a click heatmap, you can find out what your visitors think is clickable on a webpage.

  This improves conversions in two ways. 

  Firstly, it shows whether customers are clicking where you expect them to. For example, if you create a “buy now” or “free trial” button but nobody ever pushes it, it informs your back end developers that it needs an upgrade. 

  Secondly, it indicates any user experience issues. If there are a lot of clicks on an element that doesn’t link anywhere, it shows that it either needs to be changed or have a link included because customers are trying to engage with it. 

  For even more accurate data, combine click maps with hover maps. This shows where users are paying attention but not clicking through. 

  #10. Records mouse movement/hovering

  Is your website distracting users from the ultimate goal of converting ? Does your website have a logical flow and next step ? Recording mouse movement and attention will help you answer questions like these. 

  Mouse move and hover heatmaps identify where your website visitors engage on the page. Are they naturally drawn to your CTAs ? Is the sidebar taking their attention away from the primary content ? 

  This data increases the likelihood of conversions because it shows where you need to remove distractions or draw their attention in. 

  

  Final thoughts on heatmap analytics 

  Heatmap analytics benefit both you and your customers. By identifying issues that stop them from buying and optimise their engagement, you’ll have happy customers and happy stakeholders. 

  Next, check out these guides on heatmap software and using user behaviour analytics to increase conversions and improve customer experience !

  The Ultimate Guide to Heatmap Software

  How to use Behavioural Analytics to Improve Website Performance

  Heatmap Video

  Session Recording Video