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• Nginx rtmp module - on_publish fires multiple time instead of once

  29 juillet 2017, par Stephen Wright

  This is copy and pasted from the bug report I created on the rtmp-module by Arut, I am not completely sure if it is a bug or me not understanding how the module works, I have read the whole directives of module as from https://github.com/arut/nginx-rtmp-module/wiki/Directives

  Proper explanation, if code is not displayed properly I will edit and fix

  Hi, been using the module and finding it very very good !

  Think I have found a issue though, although it may be me misunderstanding the directives.

  Essentially I wish to fire a script (/usr/local/bin/make_thumbnail.sh) which creates a thumbnail automatically from a stream (using ffmpeg), the idea is to have this done for every stream as soon as it is published in order to create a function a bit like twitch tv where the streamer will not have to specify any thumbnail image, authenticated users simply start a stream (which will later be authenticated but is not yet) The script does also write data into the database however this stage works fine and I don’t believe the issue is related, if I comment out these lines then the thumbnail creation still works and my issue continues.

  Initially this was done using the "exec" command as I believe I mis-read the documentation and I believe the exec command doesn’t work for my problem as ". When publishing stops the process is terminated." does this mean it will continually execute until stream stops ?

  I have started using the exec_publish command to try and fix this issue however the same issue seems to occur. The entire script repeats approximately every 15-17 seconds, a new thumbnail is created and a new database entry is create with all the correct information.

  Below is the nginx.conf line. Please ignore if indentation is incorrect couldn’t see a way to indent blocks of code and it’s late here, assume all code is indented correctly unless you believe that could be the issue in which case I will post it indented as early as I can.

  application live {
  
  allow play all;
  
  live on;
  
  record all;
  
  record_path /var/stream/video_recordings/;
  
  record_unique on; 
  
  hls on;
  
  hls_nested on;
  
  hls_path /var/stream/HLS/live;
  
  hls_fragment 10s;
  
  
  
  #on publish create thumbnail using first second of stream and save in 
  
  /var/stream/video_recordings/thumbnails
  
  exec_publish usr/local/bin/make_thumbnail.sh $name;

  The rest can be pasted or attached if needed but is working nginx config for rtmp + website

  The most simple version of the make_thumbnail..sh is pasted below, I have omitted the variables that I have used for database entryys obviously but as the script works without fail from terminal I believe this to be an nginx issue (if I run the command manually under the nginx user e.g. sudo -u nginx /usr/local/bin/make_thumbnail.sh with a name the same as any running stream, it works and only executes once as would expect, all permissions in script are ok and tested.

  make_thumbnail.sh

  #!/bin/bash
  
  
  
  TIME=$(date +%s)
  
  NAME=$1 
  
  echo "time: "
  
  FILENAME=${TIME}_${NAME}
  
  
  
  ffmpeg -i rtmp://192.168.0.98:1935/live/$1 -vframes 1 -s 150x150 -ss 10 -
  
  strftime 1 /var/stream/video_recordings/thumbnails/"$FILENAME.jpg";
  
  
  
  #Writes path to video into database
  
  mysql --user=$DB_USER --password=$DB_PASSWD $DB_NAME << EOF
  
  INSERT INTO $TABLE3 (thumbnailfile) VALUES ('$FILENAME');
  
  set @last_id_in_thumbnails = LAST_INSERT_ID();
  
  INSERT INTO $TABLE (created_at, updated_at, thumnailID) VALUES 
  
  (NOW(),NOW(),@last_id_in_thumbnails);
  
  SET @last_id_in_livestreams = LAST_INSERT_ID();
  
  INSERT INTO $TABLE2 (created_at, updated_at, filename,liveID) VALUES 
  
  (NOW(),NOW(),'$FILENAME',@last_id_in_livestreams); 
  
  EOF

  I have not got the nginx rtmp logs installed, I can obviously do this however some of the logs appear in the nginx error.log, strangely the latest stream I tried did not update in the access log, however I think this is because I did not attempt to connect to it via any method. I don’t fully understand the error.log, in my stupidity I decided to use nginx with which I am quite inexperienced and I am finding it very difficult to troubleshoot this issue, it appears to me that as part of the RTMP protocol or my streaming software (OBS) is either directly pinging the rtmp stream or is being pinged by the server to ensure the connection is still there. And this ping is

  I have left a stream running from approx 4 minutes without interacting with the server, streaming software, computer running the stream, I have ensured the internet connection is constant as my first though was the connection dropped, however on inspecting the database the executing is done always after at least 11 seconds however usually this is 16, I can’t seem to figure out how to select the closest dates from the database however there has been at least a few 17 second differences (potentially when
  I am unsure if this is an issue or if it is intended behavior but I do require this to finish a university degree, I’m not asking for answers but if it is a legitimate issue then I would be happy to spend as much time I can commit to it if some insight into what is causing it, or if there is a workaround I believe it should be documented somewhere, I have googled into making any exec commands run only once on publish

  I can’t seem to pinpoint where in the log the issue is happening however think it is something to do with the below exceprts I would attach the file but can’t seem to select all lines after the timestamp upon starting a stream

  2017/07/26 18:17:35 [info] 1451#0: *2229 exec: starting managed child 
  
  'ffmpeg', client: 192.168.0.78, server: 0.0.0.0:1935
  
  2017/07/26 18:17:35 [info] 1451#0: *2412 client connected '192.168.0.98'
  
  2017/07/26 18:17:35 [info] 1451#0: *2412 connect: app='live' args='' 
  
  flashver='LNX 9,0,124,2' swf_url='' tc_url='rtmp://192.168.0.98:1935/live' 
  
  page_url='' acodecs=4071 vcodecs=252 object_encoding=0, client: 
  
  192.168.0.98, server: 0.0.0.0:1935
  
  2017/07/26 18:17:35 [info] 1451#0: *2412 createStream, client: 192.168.0.98, 
  
  server: 0.0.0.0:1935
  
  2017/07/26 18:17:35 [info] 1451#0: *2412 play: name='newname' args='' 
  
  start=-2000 duration=0 reset=0 silent=0, client: 192.168.0.98, server:  
  
  0.0.0.0:1935
  
  2017/07/26 18:17:36 [info] 1451#0: *2410 recv() failed (104: Connection  
  
  reset by peer), client: 192.168.0.98, server: 0.0.0.0:1935
  
  2017/07/26 18:17:36 [info] 1451#0: *2410 disconnect, client: 192.168.0.98, 
  
  server: 0.0.0.0:1935
  
  2017/07/26 18:17:36 [info] 1451#0: *2410 deleteStream, client: 192.168.0.98, 
  
  server: 0.0.0.0:1935
  
  2017/07/26 18:17:36 [notice] 1451#0: signal 17 (SIGCHLD) received
  
  2017/07/26 18:17:36 [notice] 1451#0: unknown process 10487 exited with code 
  
  0
  
  2017/07/26 18:17:36 [info] 1451#0: *2229 exec: child 10487 exited; ignoring, 
  
  client: 192.168.0.78, server: 0.0.0.0:1935
  
  
  
  ver: 0.0.0.0:1935
  
  2017/07/26 18:17:41 [info] 1451#0: *2229 exec: starting managed child 
  
  'usr/local/bin/make_thumbnail.sh', client: 192.168.0.78, server:  
  
  0.0.0.0:1935
  
  2017/07/26 18:17:41 [info] 1451#0: *2413 client connected '192.168.0.98'
  
  2017/07/26 18:17:41 [info] 1451#0: *2413 connect: app='live' args='' 
  
  flashver='LNX 9,0,124,2' swf_url='' tc_url='rtmp://192.168.0.98:1935/live' 
  
  page_url='' acodecs=4071 vcodecs=252 object_encoding=0, client: 
  
  192.168.0.98, 
  
  server: 0.0.0.0:1935
  
  2017/07/26 18:17:41 [info] 1451#0: *2413 createStream, client: 192.168.0.98, 
  
  server: 0.0.0.0:1935
  
  2017/07/26 18:17:41 [info] 1451#0: *2413 play: name='newname' args='' 
  
  start=-2000 duration=0 reset=0 silent=0, client: 192.168.0.98, server: 
  
  0.0.0.0:1935
  
  2017/07/26 18:17:43 [info] 1451#0: *2229 exec: starting managed child 
  
  'ffmpeg', 
  
  client: 192.168.0.78, server: 0.0.0.0:1935
  
  2017/07/26 18:17:43 [info] 1451#0: *2414 client connected '192.168.0.98'
  
  2017/07/26 18:17:43 [info] 1451#0: *2414 connect: app='live' args='' 
  
  flashver='LNX 9,0,124,2' swf_url='' tc_url='rtmp://192.168.0.98:1935/live' 
  
  page_url='' acodecs=4071 vcodecs=252 object_encoding=0, client: 
  
  192.168.0.98, 
  
  server: 0.0.0.0:1935
  
  @

• Elacarte Presto Tablets

  14 mars 2013, par Multimedia Mike — General

  I visited an Applebee’s restaurant this past weekend. The first thing I spied was a family at a table with what looked like a 7-inch tablet. It’s not an uncommon sight. However, as I moved through the restaurant, I noticed that every single table was equipped with such a tablet. It looked like this :

  
  
  

  For a computer nerd like me, you could probably guess that I was be far more interested in this gadget than the cuisine. The thing said “Presto” on the front and “Elacarte” on the back. Putting this together, we get the website of Elacarte, the purveyors of this restaurant tablet technology. Months after the iPad was released on 2010, I remember stories about high-end restaurants showing their wine list via iPads. This tablet goes well beyond that.

  How was it ? Well, confusing, mostly. The hostess told us we could order through the tablet or through her. Since we already knew what we wanted, she just manually took our order and presumably entered it into the system. So, right away, the question is : Do we order through a human or through a computer ? Or a combination ? Do we have to use the tablet if we don’t want to ?

  Hardware
  When picking up the tablet, it’s hard not to notice that it is very heavy. At first, I suspected that it was deliberately weighted down as some minor attempt at an anti-theft measure. But then I remembered what I know about power budgets of phones and tablets– powering the screen accounts for much of the battery usage. I realized that this device needs to drive the screen for about 14 continuous hours each day. I.e., the weight must come from a massive battery.

  The screen is good. It’s a capacitive touchscreen, so nice and responsive. When I first spied the device, I felt certain it would be a resistive touchscreen (which is more accurately called a touch-and-press-down screen). There is an AC adapter on the side of the tablet. This is the only interface to the device :

  
  
  

  That looks to me like an internal SATA connector (different from an eSATA connector). Foolishly, I didn’t have a SATA cable on me so I couldn’t verify.

  User Interface
  The interface options are : Order, Games, Neighborhood, and Pay. One big benefit of accessing the menu through the Order option is that each menu item can have a picture. For people who order more by picture than text description, this is useful. Rather, it would be, if more items had pictures. I’m not sure there were more pictures than seen in the print menu.
  
  For Games, there were a variety of party games. The interface clearly stated that we got to play 2 free games. This implied to me that further games cost money. We tried one game briefly and the food came.

  2 more options : Neighborhood– I know I dug into this option, but I forget what it was. Maybe it discussed local attractions. Finally, Pay. This thing has an integrated credit card reader. There is no integrated printer, though, so if you want one, you will have to request one from a human.

  Experience
  So we ordered through a human since we didn’t feel like being thrust into this new paradigm when we just wanted lunch. The staff was obviously amenable to that. However, I got a chance to ask them a lot of questions about the particulars. Apparently, they have had this system for about 5 months. It was confirmed that the tablets do, in fact, have gargantuan batteries that have to last through the restaurant’s entire business hours. Do they need to be charged every night ? Yes, they do. But how ? The staff described this several large charging blocks with many cables sprouting out. Reportedly, some units still don’t make it through the entire day.

  When it was time to pay, I pressed the Pay button on the interface. The bill I saw had nothing in common with what we ordered (actually, it was cheaper, so perhaps I should have just accepted it). But I pointed it out to a human and they said that this happens sometimes. So they manually printed my bill. There was a dollar charge for the game that was supposed to be free. I pointed this out and they removed it. It’s minor, I know, but it’s still worth trying to work out these bugs.

  One of the staff also described how a restaurant doesn’t need to employ as many people thanks to the tablet. She gave a nervous, awkward, self-conscious laugh when she said this. All I could think of was this Dilbert comic strip in which the boss realizes that his smartphone could perform certain key functions previously handled by his assistant.

  Not A New Idea
  Some people might think this is a totally new concept. It’s not. I was immediately reminded of my university days in Boulder, Colorado, USA, circa 1997. The local Taco Bell and Arby’s restaurants both had touchscreen ordering kiosks. Step up, interact with the (probably resistive) touchscreen, get a number, and step to the counter to change money, get your food, and probably clarify your order because there is only so much that can be handled through a touchscreen.

  What I also remember is when they tore out those ordering kiosks, also circa 1997. I don’t know the exact reason. Maybe people didn’t like them. Maybe there were maintenance costs that made them not worth the hassle.

  Then there are the widespread self-checkout lanes in grocery stores. Personally, I like those, though I know many don’t. However, this restaurant tablet thing hasn’t won me over yet. What’s the difference ? Perhaps that automated lanes at grocery stores require zero external assistance– at least, if you do everything correctly. Personally, I work well with these lanes because I can pretty much guess the constraints of the system and I am careful not to confuse the computer in any way. Until they deploy serving droids, or at least food conveyors, there still needs to be some human interaction and I think the division between the human and computer roles is unintuitive in the restaurant case.

  I don’t really care to return to the same restaurant. I’ll likely avoid any other restaurant that has these tablets. For some reason, I think I’m probably supposed to be the ideal consumer of this concept. But the idea will probably perform all right anyway. Elacarte’s website has plenty of graphs demonstrating that deploying these tablets is extremely profitable.

• The use cases for a element in HTML

  27 novembre 2012, par silvia

  The W3C HTML WG and the WHATWG are currently discussing the introduction of a <main> element into HTML.

  The <main> element has been proposed by Steve Faulkner and is specified in a draft extension spec which is about to be accepted as a FPWD (first public working draft) by the W3C HTML WG. This implies that the W3C HTML WG will be looking for implementations and for feedback by implementers on this spec.

  I am supportive of the introduction of a <main> element into HTML. However, I believe that the current spec and use case list don’t make a good enough case for its introduction. Here are my thoughts.

  Main use case : accessibility

  In my opinion, the main use case for the introduction of <main> is accessibility.

  Like any other users, when blind users want to perceive a Web page/application, they need to have a quick means of grasping the content of a page. Since they cannot visually scan the layout and thus determine where the main content is, they use accessibility technology (AT) to find what is known as “landmarks”.

  “Landmarks” tell the user what semantic content is on a page : a header (such as a banner), a search box, a navigation menu, some asides (also called complementary content), a footer, …. and the most important part : the main content of the page. It is this main content that a blind user most often wants to skip to directly.

  In the days of HTML4, a hidden “skip to content” link at the beginning of the Web page was used as a means to help blind users access the main content.

  In the days of ARIA, the aria @role=main enables authors to avoid a hidden link and instead mark the element where the main content begins to allow direct access to the main content. This attribute is supported by AT – in particular screen readers – by making it part of the landmarks that AT can directly skip to.

  Both the hidden link and the ARIA @role=main approaches are, however, band aids : they are being used by those of us that make “finished” Web pages accessible by adding specific extra markup.

  A world where ARIA is not necessary and where accessibility developers would be out of a job because the normal markup that everyone writes already creates accessible Web sites/applications would be much preferable over the current world of band-aids.

  Therefore, to me, the primary use case for a <main> element is to achieve exactly this better world and not require specialized markup to tell a user (or a tool) where the main content on a page starts.

  An immediate effect would be that pages that have a <main> element will expose a “main” landmark to blind and vision-impaired users that will enable them to directly access that main content on the page without having to wade through other text on the page. Without a <main> element, this functionality can currently only be provided using heuristics to skip other semantic and structural elements and is for this reason not typically implemented in AT.

  Other use cases

  The <main> element is a semantic element not unlike other new semantic elements such as <header>, <footer>, <aside>, <article>, <nav>, or <section>. Thus, it can also serve other uses where the main content on a Web page/Web application needs to be identified.

  Data mining

  For data mining of Web content, the identification of the main content is one of the key challenges. Many scholarly articles have been published on this topic. This stackoverflow article references and suggests a multitude of approaches, but the accepted answer says “there’s no way to do this that’s guaranteed to work”. This is because Web pages are inherently complex and many <div>, <p>, <iframe> and other elements are used to provide markup for styling, notifications, ads, analytics and other use cases that are necessary to make a Web page complete, but don’t contribute to what a user consumes as semantically rich content. A <main> element will allow authors to pro-actively direct data mining tools to the main content.

  Search engines

  One particularly important “data mining” tool are search engines. They, too, have a hard time to identify which sections of a Web page are more important than others and employ many heuristics to do so, see e.g. this ACM article. Yet, they still disappoint with poor results pointing to findings of keywords in little relevant sections of a page rather than ranking Web pages higher where the keywords turn up in the main content area. A <main> element would be able to help search engines give text in main content areas a higher weight and prefer them over other areas of the Web page. It would be able to rank different Web pages depending on where on the page the search words are found. The <main> element will be an additional hint that search engines will digest.

  Visual focus

  On small devices, the display of Web pages designed for Desktop often causes confusion as to where the main content can be found and read, in particular when the text ends up being too small to be readable. It would be nice if browsers on small devices had a functionality (maybe a default setting) where Web pages would start being displayed as zoomed in on the main content. This could alleviate some of the headaches of responsive Web design, where the recommendation is to show high priority content as the first content. Right now this problem is addressed through stylesheets that re-layout the page differently depending on device, but again this is a band-aid solution. Explicit semantic markup of the main content can solve this problem more elegantly.

  Styling

  Finally, naturally, <main> would also be used to style the main content differently from others. You can e.g. replace a semantically meaningless <div id=”main”> with a semantically meaningful <main> where their position is identical. My analysis below shows, that this is not always the case, since oftentimes <div id=”main”> is used to group everything together that is not the header – in particular where there are multiple columns. Thus, the ease of styling a <main> element is only a positive side effect and not actually a real use case. It does make it easier, however, to adapt the style of the main content e.g. with media queries.

  Proposed alternative solutions

  It has been proposed that existing markup serves to satisfy the use cases that <main> has been proposed for. Let’s analyse these on some of the most popular Web sites. First let’s list the propsed algorithms.

  Proposed solution No 1 : Scooby-Doo

  On Sat, Nov 17, 2012 at 11:01 AM, Ian Hickson <ian@hixie.ch> wrote :
  | The main content is whatever content isn’t
  | marked up as not being main content (anything not marked up with <header>,
  | <aside>, <nav>, etc).
  

  This implies that the first element that is not a <header>, <aside>, <nav>, or <footer> will be the element that we want to give to a blind user as the location where they should start reading. The algorithm is implemented in https://gist.github.com/4032962.

  Proposed solution No 2 : First article element

  On Sat, Nov 17, 2012 at 8:01 AM, Ian Hickson <ian@hixie.ch> wrote :
  | On Thu, 15 Nov 2012, Ian Yang wrote :
  | >
  | > That’s a good idea. We really need an element to wrap all the <p>s,
  | > <ul>s, <ol>s, <figure>s, <table>s ... etc of a blog post.
  |
  | That’s called <article>.
  

  This approach identifies the first <article> element on the page as containing the main content. Here’s the algorithm for this approach.

  Proposed solution No 3 : An example heuristic approach

  The readability plugin has been developed to make Web pages readable by essentially removing all the non-main content from a page. An early source of readability is available. This demonstrates what a heuristic approach can perform.

  Analysing alternative solutions

  Comparison

  I’ve picked 4 typical Websites (top on Alexa) to analyse how these three different approaches fare. Ideally, I’d like to simply apply the above three scripts and compare pictures. However, since the semantic HTML5 elements <header>, <aside>, <nav>, and <footer> are not actually used by any of these Web sites, I don’t actually have this choice.

  So, instead, I decided to make some assumptions of where these semantic elements would be used and what the outcome of applying the first two algorithms would be. I can then compare it to the third, which is a product so we can take screenshots.

  Google.com

  http://google.com – search for “Scooby Doo”.

  The search results page would likely be built with :

  • a <nav> menu for the Google bar
  • a <header> for the search bar
  • another <header> for the login section
  • another <nav> menu for the search types
  • a <div> to contain the rest of the page
  • a <div> for the app bar with the search number
  • a few <aside>s for the left and right column
  • a set of <article>s for the search results

  “Scooby Doo” would find the first element after the headers as the “main content”. This is the element before the app bar in this case. Interestingly, there is a <div @id=main> already in the current Google results page, which “Scooby Doo” would likely also pick. However, there are a nav bar and two asides in this div, which clearly should not be part of the “main content”. Google actually placed a @role=main on a different element, namely the one that encapsulates all the search results.

  “First Article” would find the first search result as the “main content”. While not quite the same as what Google intended – namely all search results – it is close enough to be useful.

  The “readability” result is interesting, since it is not able to identify the main text on the page. It is actually aware of this problem and brings a warning before displaying this page :

  

  Facebook.com

  https://facebook.com

  A user page would likely be built with :

  • a <header> bar for the search and login bar
  • a <div> to contain the rest of the page
  • an <aside> for the left column
  • a <div> to contain the center and right column
  • an <aside> for the right column
  • a <header> to contain the center column “megaphone”
  • a <div> for the status posting
  • a set of <article>s for the home stream

  “Scooby Doo” would find the first element after the headers as the “main content”. This is the element that contains all three columns. It’s actually a <div @id=content> already in the current Facebook user page, which “Scooby Doo” would likely also pick. However, Facebook selected a different element to place the @role=main : the center column.

  “First Article” would find the first news item in the home stream. This is clearly not what Facebook intended, since they placed the @role=main on the center column, above the first blog post’s title. “First Article” would miss that title and the status posting.

  The “readability” result again disappoints but warns that it failed :

  

  YouTube.com

  http://youtube.com

  A video page would likely be built with :

  • a <header> bar for the search and login bar
  • a <nav> for the menu
  • a <div> to contain the rest of the page
  • a <header> for the video title and channel links
  • a <div> to contain the video with controls
  • a <div> to contain the center and right column
  • an <aside> for the right column with an <article> per related video
  • an <aside> for the information below the video
  • a <article> per comment below the video

  “Scooby Doo” would find the first element after the headers as the “main content”. This is the element that contains the rest of the page. It’s actually a <div @id=content> already in the current YouTube video page, which “Scooby Doo” would likely also pick. However, YouTube’s related videos and comments are unlikely to be what the user would regard as “main content” – it’s the video they are after, which generously has a <div id=watch-player>.

  “First Article” would find the first related video or comment in the home stream. This is clearly not what YouTube intends.

  The “readability” result is not quite as unusable, but still very bare :

  

  Wikipedia.com

  http://wikipedia.com (“Overscan” page)

  A Wikipedia page would likely be built with :

  • a <header> bar for the search, login and menu items
  • a <div> to contain the rest of the page
  • an &ls; article> with title and lots of text
  • <article> an <aside> with the table of contents
  • several <aside>s for the left column

  Good news : “Scooby Doo” would find the first element after the headers as the “main content”. This is the element that contains the rest of the page. It’s actually a <div id=”content” role=”main”> element on Wikipedia, which “Scooby Doo” would likely also pick.

  “First Article” would find the title and text of the main element on the page, but it would also include an <aside>.

  The “readability” result is also in agreement.

  

  Results

  In the following table we have summarised the results for the experiments :

  Site	Scooby-Doo	First article	Readability
  Google.com	FAIL	SUCCESS	FAIL
  Facebook.com	FAIL	FAIL	FAIL
  YouTube.com	FAIL	FAIL	FAIL
  Wikipedia.com	SUCCESS	SUCCESS	SUCCESS

  Clearly, Wikipedia is the prime example of a site where even the simple approaches find it easy to determine the main content on the page. WordPress blogs are similarly successful. Almost any other site, including news sites, social networks and search engine sites are petty hopeless with the proposed approaches, because there are too many elements that are used for layout or other purposes (notifications, hidden areas) such that the pre-determined list of semantic elements that are available simply don’t suffice to mark up a Web page/application completely.

  Conclusion

  It seems that in general it is impossible to determine which element(s) on a Web page should be the “main” piece of content that accessibility tools jump to when requested, that a search engine should put their focus on, or that should be highlighted to a general user to read. It would be very useful if the author of the Web page would provide a hint through a <main> element where that main content is to be found.

  I think that the <main> element becomes particularly useful when combined with a default keyboard shortcut in browsers as proposed by Steve : we may actually find that non-accessibility users will also start making use of this shortcut, e.g. to get to videos on YouTube pages directly without having to tab over search boxes and other interactive elements, etc. Worthwhile markup indeed.