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• FFMPEG : Invalid Pixel Format String -1 when converting MP3 to SWF

  22 janvier 2013, par James Riley

  I'm having an issue with FFMPEG - receiving an error when trying to convert an MP3 into an SWF. The full output contains :

  $ ffmpeg -i track1.mp3 -y -ar '44100' -ab '96k' 'sample.swf'
  
      FFmpeg version SVN-r26402, Copyright (c) 2000-2011 the FFmpeg developers
  
      configuration: --enable-libmp3lame --enable-libvorbis --enable-shared --disable-mmx
  
      libavutil     50.36. 0 / 50.36. 0
  
      libavcore      0.16. 1 /  0.16. 1
  
      libavcodec    52.108. 0 / 52.108. 0
  
      libavformat   52.93. 0 / 52.93. 0
  
      libavdevice   52. 2. 3 / 52. 2. 3
  
      libavfilter    1.74. 0 /  1.74. 0
  
      libswscale     0.12. 0 /  0.12. 0
  
      Input #0, nsv, from 'track1.mp3':
  
       Metadata:
  
         encoder         : Lavf52.93.0
  
         artist          : Test
  
         title           : Track02
  
         album           : Mixtape
  
         disc            : 1/1
  
         genre           : Acoustic
  
         date            : 2013
  
         track           : 2/2
  
         album_artist    : Test
  
         Duration: 00:00:00.00, start: 0.000000, bitrate: -2147483 kb/s
  
         Stream #0.0: Video: [216][195]2[138] / 0x8A32C3D8, 44318x50468, 24 fps, 24 tbr, 24 tbn, 24 tbc
  
         Stream #0.1: Audio: h[228][146][142] / 0x8E92E468, 0 channels
  
      [buffer @ 0x175cd00] Invalid pixel format string '-1'
  
      Error opening filters!

  I'm aware the FFmpeg version here is old, but the issue is only occuring for one of the MP3s I am testing here. I have many others that are working just fine.

  What can be causing this issue and what steps can I take to resolve this ?

  From what I understand, the pixel format relates to the video output, yet in this case, the SWF is only to be used for audio. I've tested this on a newer version of FFmpeg and the issue isn't occuring - I certainly plan to upgrade FFmpeg on the test server I'm using, but would like to get to the bottom of why this is happening and try to get this particular MP3 converting, where its currently failing despite many others not having the same issue.

  Thanks for any help !

• Breaking a video into frames with python

  30 juillet 2012, par user1481112

  I am trying to write a program that deletes frames of a video that don't have a particular symbol in them. My general plan :

  1. Split the audio from the video
  2. Split the video into frames
  3. Run the frames through a subroutine that looks for the symbol, by checking the pixels where it should be for being the correct color, and logging the ones that don't.
  4. Delete those frames and corresponding audio seconds
  5. Splices it all back together.

  I need some help finding libraries that can do this. I was wondering if wxpython could do the detection of pixel color. I have no idea what library could split audio and video and which could edit audio. I know ffmpeg could split the video into frames but after two days of work I still have not been able to install it for python 2.7, so I either need a way to install it or a different library to do it. Any ideas ?

• 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.