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• WebVTT Discussions at FOMS

  18 décembre 2013, par silvia

  At the recent FOMS (Foundations of Open Media Software and Standards) Developer Workshop, we had a massive focus on WebVTT and the state of its feature set. You will find links to summaries of the individual discussions in the FOMS Schedule page. Here are some of the key results I went away with.

  1. WebVTT Regions

  The key driving force for improvements to WebVTT continues to be the accurate representation of CEA608/708 captioning. As part of that drive, we’ve introduced regions (the CEA708 “window” concept) to WebVTT. WebVTT regions satisfy multiple requirements of CEA608/708 captions :

  1. support for rollup captions
  2. support for background color and border color on a group of cues independent of the background color of the individual cue
  3. possibility to move a group of cues from one location on screen to a different
  4. support to specify an anchor point and a growth direction for cues when their text size changes
  5. support for specifying a fixed number of lines to be rendered
  6. possibility to specify which region is rendered in front of which other one when regions overlap

  While WebVTT regions enable us to satisfy all of the above points, the specification isn’t actually complete yet and some of the above needs aren’t satisfied yet.

  We have an open bug to move a region elsewhere. A first discussion at FOMS seemed to to indicate that we’ll have to add syntax for updating a region at a particular time and thus give region definitions a way to be valid only for a certain time frame. I can imagine that the region definitions that we have in the header of the WebVTT file now would have an implicitly defined time frame from the start to the end of the file, but can be overruled by a re-definition anywhere within the WebVTT file. That redefinition needs to provide a start and end time.

  We registered a bug to add specifying the width and height of regions (and possibly of cues) by em (i.e. by multiples of the largest character in a font). This should allow us to have the region grow/shrink around the region anchor point with a change of font size by script or a user. em specifications should also be applied to cues – that matches the column count of CEA708/608 better.

  When regions overlap, the original region extension spec already suggested a “layer” cue setting. It will be easy to add it.

  Another change that we will ultimately need is the “scroll” setting : we will need to introduce support for scrolling text down or from left-to-right or right-to-left, e.g. vertical scrolling text seems to be used in some Chinese caption use cases.

  2. Unify Rendering Approach

  The introduction of regions created a second code path in the rendering spec with some duplication. At FOMS we discussed if it was possible to unify that. The suggestion is to render all cues into a region. Those that are not part of a region would be rendered into an anonymous region that covers the complete viewport. There may be some consequences to this, e.g. cue settings should be usable across all cues, no matter whether or not part of a region, and avoiding cue overlap may need to be done within regions.

  Here’s a rough outline of the path of the new rendering algorithm :

  (1) Render the regions :

  Specified Region	Anonymous Region
  Render values as given :	Render following values :
  width lines regionanchor viewportanchor scroll	100% videoheight/lineheight 0,0 0,0 none

  (2) Render the cues :

  • Create a cue box and put it in its region (anonymous if none given).
  • Calculate position & size of cue box from cue settings (position, line, size).
  • Calculate position of cue text inside cue box from remaining cue settings (vertical, align).

  3. Vertical Features

  WebVTT includes vertical rendering, both right-to-left and left-to-right. However, regions are not defined for vertical. Eventually, we’re going to have to look at the vertical features of WebVTT with more details and figure out whether the spec is working for them and what real-world requirements we have missed. We hope we can get some help from users in countries where vertically rendered captions/subtitles are the norm.

  4. Best Practices

  Some of he WebVTT users at FOMS suggested it would be advantageous to start a list of “best practices” for how to author captions with WebVTT. Example recommendations are :

  • Use line numbers only to position cues from top or bottom of viewport. Don’t use otherwise.
  • Note that when the user increases the fontsize in rollup captions and thus introduces new line breaks, your cues will roll by faster because the number of lines of a rollup is fixed.
  • Make sure to use &lrm ; and &rlm ; UTF-8 markers to control the directionality of your text.

  It would be nice if somebody started such a document.

  5. Non-caption use cases

  Instead of continuing to look back and improve our support of captions/subtitles in WebVTT, one session at FOMS also went ahead and looked forward to other use cases. The following requirements came out of this :

  5.1 Preview Thumbnails

  A common use case for timed data is the use of preview thumbnails on the navigation bar of videos. A native implementation of preview thumbnails would allow crawlers and search engines to have a standardised way of extracting timed images for media files, so introduction of a new @kind value “thumbnails” was suggested.

  The content of a “thumbnails” cue could be any of :

  • an image URL
  • a sprite URL to a single image
  • a spatial & temporal media fragment URL to a media resource
  • base64 encoded image (data URI)
  • an iframe offset to the media resource

  The suggestion is to allow anything that would work in a img @src attribute as value in a cue of @kind=”thumbnails”. Responsive images might also be useful for a track of @kind=”thumbnails”. It may even be possible to define an inband thumbnail track based on the track of @kind=”thumbnails”. Such cues should also work in the JavaScript track API.

  5.2 Chapter markers

  There is interest to put richer content than just a chapter title into chapter cues. Often, chapters consist of a title, text and and image. The text is not so important, but the image is used almost everywhere that chapters are used. There may be a need to extend chapter cue content with images, similar to what a @kind=”thumbnails” track offers.

  The conclusion that we arrived at was that we need to make @kind=”thumbnails” work first and then look at using the learnings from that to extend @kind=”chapters”.

  5.3 Inband tracks for live video

  A difficult topic was opened with the question of how to transport text tracks in live video. In live captioning, end times are never created for cues, but are implied by the start time of the next cue. This is a use case that hasn’t been addressed in HTML5/WebVTT yet. An old proposal to allow a special end time value of “NEXT” was discussed and recommended for adoption. Also, there was support for the spec change that stops blocking loading VTT until all cues have been loaded.

  5.4 Cross-domain VTT loading

  A brief discussion centered around the fact that the spec disallows cross-domain loading of WebVTT files, but that no browser implements this. This needs to be discussion at the HTML WG level.

  6. Regions in live captioning

  The final topic that we discussed was how we could provide support for regions in live captioning.

  • The currently active region definitions will need to be come part of every header of every VTT file segment that HLS uses, so it’s available in case the cues in the segment file reference it.
  • “NEXT” in end time markers would make authoring of live captioned VTT files easier.
  • If the application wants to use 1 word at a time and doesn’t want to delay sending the word until the full cue is authored (e.g. in a Hangout type environment), we will need to introduce the concept of “cue continuation markers”, so we know that a cue could be extended with the next VTT file fragment.

  This is an extensive and impressive amount of discussion around WebVTT and a lot of new work to be performed in the future. I’m very grateful for all the people who have contributed to these discussions at FOMS and will hopefully continue to help get the specifications right.

• need help on solving my ffmpeg command line

  3 avril 2019, par DRMTV

  i create a small bash script to encode 1080p video , the video will be added with watermark at bottom left and i need to add a black padding on top and bottom

  i tried several way but still no luck , i tried -vf and yes it worked but cant use padding and watermark together , and suggest use filter_complex

  if i use this code directly without bash script it work

  time ffmpeg -hide_banner -i transformers.mp4 -i transformers.ass -loop 1 -i watermark.png -loop 1 -i logo.png -map 0:0 -map 0:1 -filter_complex "[0:0]scale=(iw*sar)*min(1920/(iw*sar)\,800/ih):ih*min(1920/(iw*sar)\,800/ih), pad=1920:800:(1920-iw*min(1920/iw\,800/ih))/2:(800-ih*min(1920/iw\,800/ih))/2;ass=transformers.ass[FID1];[FID1][2:v]overlay=10:${WATERMARKPOSITION}:repeatlast=0:enable='between(t,300,600)'[FID3];[3:v]fade=in:st=1200:d=1.6:alpha=1,fade=out:st=107998:d=1.6:alpha=1[FID6];[FID3][FID6]overlay=10:5:repeatlast=0:enable='between(t,1200,187922)'" -c:v libx264 -minrate 1800k -maxrate 1800k -bufsize 3600k -profile:v high -c:a aac -b:a 128k -profile:a aac_main -movflags faststart -strict -2 -f mp4 -y "transformers.mp4"

  but when i include it with my bash script i got this error ,

  [libx264 @ 0x2a063e0] height not divisible by 2 (300x39)
  
  Output #0, mp4, to '/movie/Paddy/output/Transformers.Age.of.Extinction.2014.1080p.BluRay.H264.AAC-RARBG.mp4':
  
    Metadata:
  
      major_brand     : isom
  
      minor_version   : 512
  
      compatible_brands: isomiso2avc1mp41
  
      comment         : Transformers.Age.of.Extinction.2014.1080p.BluRay.H264.AAC-RARBG
  
      encoder         : Lavf57.71.100
  
      title           : Transformers Age of Extinction 2014 1080p BluRay H264 AAC-RARBG - Visit us @ Juraganfilm.COM
  
      Stream #0:0: Video: h264 (libx264), yuv420p, 1920x800 [SAR 1:1 DAR 12:5], q=-1--1, max. 2300 kb/s, 23.98 fps, 23.98 tbn, 23.98 tbc
  
      Metadata:
  
        encoder         : Lavc56.60.100 libx264
  
      Stream #0:1: Video: h264, none, q=2-31, 128 kb/s, SAR 1:1 DAR 0:0, 25 fps
  
      Metadata:
  
        encoder         : Lavc56.60.100 libx264
  
      Stream #0:2(eng): Audio: aac, 0 channels, 128 kb/s (default)
  
      Metadata:
  
        creation_time   : 2017-12-19 07:58:39
  
        handler_name    : SoundHandler
  
        encoder         : Lavc56.60.100 aac
  
  Stream mapping:
  
    Stream #0:0 (h264) -> scale (graph 0)
  
    Stream #0:0 (h264) -> overlay:overlay (graph 0)
  
    Stream #2:0 (png) -> ass (graph 0)
  
    Stream #3:0 (png) -> fade (graph 0)
  
    pad (graph 0) -> Stream #0:0 (libx264)
  
    overlay (graph 0) -> Stream #0:1 (libx264)
  
    Stream #0:1 -> #0:2 (aac (native) -> aac (native))
  
  Error while opening encoder for output stream #0:1 - maybe incorrect parameters such as bit_rate, rate, width or height

  and below is the script i have been working on

  output="/movie/output"
  
  
  
  FILESDIR=`find $PWD -type f -regex ".*\.\(mp4\|mkv\|avi\)" | sed 's@.*/@@' | sort -n`
  
  for video in $FILESDIR
  
  do
  
  
  
  MOVIETITLE=${video%.*}
  
  INFOVID=${MOVIETITLE//./ }
  
  BITRATE="${HEIGHT}"
  
  WIDTH=$(ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 ${video} 2>&1 | sed -e 's|\[.*||g' | sed ':a;N;$!ba;s/\n//g' | sed -e 's|x.*||g')
  
  HEIGHT=$(ffprobe -v error -select_streams v:0 -show_entries stream=width,height -of csv=s=x:p=0 ${video} | sed -e 's/.*x//')
  
  WATERMARKPOSITION=$(expr $HEIGHT - 50)
  
  VIDEOMAP=$(ffmpeg -i $video 2>&1 | grep "Stream #" | grep Video | sed -e "s|.*\#||g" | sed -e "s|: Video.*||g" | sed -e "s|(.*||g")
  
  AUDIOMAP=$(ffmpeg -i $video 2>&1 | grep "Stream #" | grep Audio | sed -e "s|.*\#||g" | sed -e "s|: Audio.*||g" | sed -e "s|(.*||g")
  
  MAXRATE=$(expr $BITRATE + 500)
  
  BUFFSIZE=$(expr $MAXRATE \* 2)
  
  
  
  time ffmpeg -hide_banner -i $video -i $MOVIETITLE.ass -loop 1 -i $WATERMARK -loop 1 -i $LOGO -map ${VIDEOMAP} -map ${AUDIOMAP} -filter_complex "[${VIDEOMAP}]scale=(iw*sar)*min(${WIDTH}/(iw*sar)\,${HEIGHT}/ih):ih*min(${WIDTH}/(iw*sar)\,${HEIGHT}/ih), pad=${WIDTH}:${HEIGHT}:(${WIDTH}-iw*min(${WIDTH}/iw\,${HEIGHT}/ih))/2:(${HEIGHT}-ih*min(${WIDTH}/iw\,${HEIGHT}/ih))/2;ass=$MOVIETITLE.ass[FID1];[FID1][2:v]overlay=10:${WATERMARKPOSITION}:repeatlast=0:enable='between(t,300,600)'[FID3];[3:v]fade=in:st=1200:d=1.6:alpha=1,fade=out:st=107998:d=1.6:alpha=1[FID6];[FID3][FID6]overlay=10:5:repeatlast=0:enable='between(t,1200,187922)'" -c:v libx264 -minrate ${BITRATE}k -maxrate ${MAXRATE}k -bufsize ${BUFFSIZE}k -profile:v high -c:a aac -b:a 128k -profile:a aac_main -movflags faststart -strict -2 -f mp4 -y "${output}/$MOVIETITLE.mp4"
  
  done

  has been working all day and still i cant make it to work.

  can someone guide me which part is wrong ?

• Spotlight : Alwaysdata.com the company behind Piwik.org web hosting [Interview]

  11 avril 2013, par matt — About, Community

  Piwik is the result of the work of many talented individuals and companies. Today we’d like to showcase Alwaysdata.com, the awesome web hosting company providing managed hosting for all Piwik.org websites and services.

  I recently met and asked a few questions to Cyril, co-founder of Alwaysdata.com and Piwik core developer. Learn more in the interview below !

  

  1. What is Alwaysdata ?
  2. Who are your customers and what kind of work do you do ?
  3. What sets Alwaysdata apart from the large web hosting competition ?
  4. Are you using Piwik internally or with customers ? If so, how are you using Piwik ?
  5. What is the next big thing for Alwaysdata ?
  6. Learn more

  What is Alwaysdata ?

  We are a French web hosting company created in 2006. If you need to host a website — a Piwik installation, for example — or even your domains/emails, we provide infrastructure and maintenance services.

  Who are your customers and what kind of work do you do ?

  We have several types of clients :

  • Individuals who need hosting for their personal site and who benefit from storage space with direct SSH access.
  • Web agencies who need hosting for their clients’ sites.
  • The largest customers, often on dedicated servers, for hosting their site/infrastructure.

  Our work falls into three categories :

  1. Support (via administration, telephone, Twitter, IRC, etc.)
  2. Development (in Python), primarily to add new features
  3. System administration, either for maintenance (e.g. adding servers), or for preparing new features

  What sets Alwaysdata apart from the large web hosting competition ?

  Two things :

  • Availability. We are a small team and often know our customers quite well. We are all on IRC, so you can contact us directly if you need any assistance.
  • Features. We are halfway between traditional web hosting and the cloud, combining the advantages of both.

  Are you using Piwik internally or with customers ? If so, how are you using Piwik ?

  All of our customers can view statistics for their sites via our global Piwik installation, without having to configure anything.

  To provide these analytics reports to our customers, we implemented import of the raw access logs in Piwik. The Log import toolkit is now a feature included in Piwik.

  What is the next big thing for Alwaysdata ?

  We are going to upgrade our pricing : instead of fixed costs, each of our clients will now pay exactly what they consume. This allows our clients the benefit of a very high quality service for the lowest possible price.

  We are also going to add native support for more technologies : Java, Node.js, ZeroMQ, etc.

  Thank you for your time and all the best to Alwaysdata for the future !

  —

  Note from Matt, Piwik founder : Cyril and the team at Alwaysdata.com have been consistently great in their system administration work for Piwik.org services, providing a fast and reliable web hosting experience with top notch support and security practises. They also handled the migration of all services from our old servers with total piece of mind.

  Alwaysdata contributed to Piwik the popular Log Analytics toolkit. They are great software developers and system administrators with a passion for their work. Since 2006, they have been maintaining optimized hosting services for the entire web infrastructure (websites, domains, emails, databases, etc.), from the simplest to the most exotic. We do recommend their managed hosting services.

  Learn more

  • Visit their website at Alwaysdata.com
  • Learn more about their Managed hosting on dedicated servers
  • Learn more about other companies and individuals who make a difference in Piwik.