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• Web-based video editor

  10 octobre 2014, par Danny

  We have a web-based editor currently that allows users to build animated web apps. The apps are made up of shapes, text, images, and videos. Except for videos, all other elements can also be animated around the screen. The result of building a animated app is basically a big blob of JSON.

  The playback code for the web app is web-based as well. It takes the JSON blob and constructs the HTML, which ends up playing back in some sort of browser environment. The problem is that most of the time this playback occurs on lower-end hardware like televisions and set-top boxes.

  These performance issues go away if there is some way to be able to convert a digital sign to video. Then the STB/smart TV simply plays a video, which is much more performant than playing back animations in a web view.

  Given a blob of JSON describing each layer and how to draw each type of object, its animation points, etc, how could I somehow take that and convert it to video on the server ?

  My first attempt at this was using PhantomJS to load the playback page in a headless browser, take a series of screenshots, and then use ffmpeg to merge those screenshots into a video. That worked great so long as there is no video. But it does not work with video since there is no HTML5 video tag support in PhantomJS, and even if there was, I would lose any audio.

  The other way I was thinking of doing it would be to again load the playback page in PhantomJS, but turn off the video layers and leave them transparent, then take screenshots as a series of PNGs with transparency. I would then combine these with the video layers.

  None of this feels very elegant though. I know there are web-based video editors out there that basically do what I’m trying to accomplish, so how do they do it ?

• Web-based video editor

  13 avril 2021, par Danny

  We have a web-based editor currently that allows users to build animated web apps. The apps are made up of shapes, text, images, and videos. Except for videos, all other elements can also be animated around the screen. The result of building a animated app is basically a big blob of JSON.

  



  The playback code for the web app is web-based as well. It takes the JSON blob and constructs the HTML, which ends up playing back in some sort of browser environment. The problem is that most of the time this playback occurs on lower-end hardware like televisions and set-top boxes.

  



  These performance issues go away if there is some way to be able to convert a digital sign to video. Then the STB/smart TV simply plays a video, which is much more performant than playing back animations in a web view.

  



  Given a blob of JSON describing each layer and how to draw each type of object, its animation points, etc, how could I somehow take that and convert it to video on the server ?

  



  My first attempt at this was using PhantomJS to load the playback page in a headless browser, take a series of screenshots, and then use ffmpeg to merge those screenshots into a video. That worked great so long as there is no video. But it does not work with video since there is no HTML5 video tag support in PhantomJS, and even if there was, I would lose any audio.

  



  The other way I was thinking of doing it would be to again load the playback page in PhantomJS, but turn off the video layers and leave them transparent, then take screenshots as a series of PNGs with transparency. I would then combine these with the video layers.

  



  None of this feels very elegant though. I know there are web-based video editors out there that basically do what I'm trying to accomplish, so how do they do it ?

  


• avutils/hwcontext : When deriving a hwdevice, search for existing device in both direc...

  25 novembre 2021, par Soft Works

  avutils/hwcontext : When deriving a hwdevice, search for existing device in both directions
  The test /libavutil/tests/hwdevice checks that when deriving a device
  
  from a source device and then deriving back to the type of the source
  
  device, the result is matching the original source device, i.e. the
  
  derivation mechanism doesn't create a new device in this case.
  Previously, this test was usually passed, but only due to two different
  
  kind of flaws :
  1. The test covers only a single level of derivation (and back)
  It derives device Y from device X and then Y back to the type of X and
  
  checks whether the result matches X.
  What it doesn't check for, are longer chains of derivation like :
  CUDA1 > OpenCL2 > CUDA3 and then back to OpenCL4
  In that case, the second derivation returns the first device (CUDA3 ==
  
  CUDA1), but when deriving OpenCL4, hwcontext.c was creating a new
  
  OpenCL4 context instead of returning OpenCL2, because there was no link
  
  from CUDA1 to OpenCL2 (only backwards from OpenCL2 to CUDA1)
  If the test would check for two levels of derivation, it would have
  
  failed.
  This patch fixes those (yet untested) cases by introducing forward
  
  references (derived_device) in addition to the existing back references
  
  (source_device).
  2. hwcontext_qsv didn't properly set the source_device
  In case of QSV, hwcontext_qsv creates a source context internally
  
  (vaapi, dxva2 or d3d11va) without calling av_hwdevice_ctx_create_derived
  
  and without setting source_device.
  This way, the hwcontext test ran successful, but what practically
  
  happened, was that - for example - deriving vaapi from qsv didn't return
  
  the original underlying vaapi device and a new one was created instead :
  
  Exactly what the test is intended to detect and prevent. It just
  
  couldn't do so, because the original device was hidden (= not set as the
  
  source_device of the QSV device).
  This patch properly makes these setting and fixes all derivation
  
  scenarios.
  (at a later stage, /libavutil/tests/hwdevice should be extended to check
  
  longer derivation chains as well)
  Reviewed-by : Lynne <dev@lynne.ee>
  
  Reviewed-by : Anton Khirnov <anton@khirnov.net>
  
  Tested-by : Wenbin Chen <wenbin.chen@intel.com>
  
  Signed-off-by : softworkz <softworkz@hotmail.com>
  
  Signed-off-by : Haihao Xiang <haihao.xiang@intel.com>
  

  • [DH] libavutil/hwcontext.c
  • [DH] libavutil/hwcontext.h
  • [DH] libavutil/hwcontext_internal.h
  • [DH] libavutil/hwcontext_qsv.c