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• Expand (extend) a video to an specific duration

  8 février 2013, par BorrajaX

  Do VLC or FFmpeg (or AVconv) have any feature to force the duration of a video to a certain number of seconds ?

  Let's say I have a... 5 minutes .mp4 video (without audio). Is there a way to have any of the aforementioned tools "expanding" the video to a longer duration ? The video comes from a Power Point slideshow, but it's too short (running too fast, to say so). The idea would be automatically inserting frames so it reaches an specified duration. It looks like something pretty doable (erm... for a total newbie in video encoding/transcoding as I am) : A 5 minutes video, at 30fps means I have 9000 frames... To make it be 10 times longer, get the first "real" frame, copy it ten times, then get the second "real" frame, copy it ten times... and so on.

  I'm using Ubuntu 12.04, but I can install/compile any required software, if needed. So far, I have VLC, AVConv and FFmpeg (FFmpeg in an specific folder, so it won't conflict with AVConv)

  Thank you in advance.

• lavc/opusdsp : simplify R-V V postfilter

  16 décembre 2023, par Rémi Denis-Courmont

  lavc/opusdsp : simplify R-V V postfilter
  This skips the round-trip to scalar register for the sliding 'x'
  
  coefficients, improving performance by about 5%. The trick here is that
  
  the vector slide-up instruction preserves elements in destination vector
  
  until the slide offset.
  The switch from vfslide1up.vf to vslideup.vi also allows the elimination
  
  of data dependencies on consecutive slides. Since the specifications
  
  recommend sticking to power of two offsets, we could slide as follows :
          vslideup.vi v8, v0, 2
  
          vslideup.vi v4, v0, 1
  
          vslideup.vi v12, v8, 1
  
          vslideup.vi v16, v8, 2
  However in the device under test, this seems to make performance slightly
  
  worse, so this is left for (in)validation with future better hardware.
  

  • [DH] libavcodec/riscv/opusdsp_rvv.S

• Why does my Blink based browser play hide and seek ?

  21 janvier 2016, par Caius Jard

  We have a C# tool (that I wrote) that records online broadcasts taking place a custom written (that we wrote) flash app. (There are no DRM or copyright issues here.)

  We’ve coded up a system whereby this tool is installed on a Windows Server 2012 R2 Amazon AWS instance. After we boot the instance, the tool loads, waits for the right time to start recording, launches a browser and passes the command line argument of the URL to access the broadcast. The browser will then load the flash app and the interview audio and video will start arriving at the browser instance on AWS

  By way of a virtual audio cable driver, screen / audio capture directshow filters and ffmpeg a screen recording is taken. The C# tool calls ffmpeg and ffmpeg will record the screen reliably for the entire interview, then the tool shuts the whole thing down

  The problem I’m having is that both Chrome and Electron browser sometimes simply don’t draw themselves on the screen so all ffmpeg ends up recording is a blank desktop and the audio of the broadcast (hence, the browser IS running)

  We found this out when recordings started turning up with X hours of merely recording the windows desktop and the tool’s main window with a countdown timer.

  A screenshotting facility was built into the tool and added to its web control interface, and this way we can test whether the browser is visible - a human looks at the screenshot of every broadcast, just after recording has started (the browser is supposed to be on show by this time)

  We notice that 50% of the time, the browser isn’t drawing itself on screen. By 50% I mean that every other recording that the AWS instance carries out, will be blank : AWS starts, records ok, shuts down. AWS starts again an hour later for a different broadcast, recording is blank, shuts down.. Starts/ok/shutdown. Starts/blank/shutdown. Repeat ad infinitum

  What’s even more strange is that if I run VNCviewer on my dev machine and connect up to an instance that is having a problem, the instant that the VNC connection is up and the remote desktop is showing on my screen, the browser suddenly appears as if nothing was ever wrong. A screenshot from before the VNC connect shows blank desktop, connect VNC, take another screenshot and the browser is there. All through it the audio is fine - the browser connected to the boadcast is fine, for sure

  It’s as though Chrome/Electron thinks "you know what, noone is looking at me so I’m not going to bother drawing myself". No screen saver is set, though the power plan has the setting "turn off the display after 15 minutes".

  Perhaps Chrome/Electron have a test amounts to "if the display is off, don’t draw". I can’t explain the inconsistency though - the recorder launches at least 1 hour before it’s needed, and sits there idle until it’s time to start the browser. You’d hence imagine that the "power off the monitor after 15 mins" setting would reliably have ensured the "monitor" is "off" by the time every recording start comes around

  This behaviour doesn’t happen with any of the other browsers (but unfortunately the app doesn’t and cannot work in them because it uses some weird chrome-only technology/API).

  Can anyone suggest anything to look at to help debug this, or anything I can build into the C# tool to overcome the problem ? Coding it up to connect to itself via VNC for a few seconds after it has launched the browser.. Well that just tastes nasty.

  Naturally, as soon as I connect to the machine via VNC (rather than RDP - RDP isn’t usable because the recording context is in a logged on session for a particular user) the problem goes away, which makes it frustratingly hard to debug.