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• Use FFMPEG to stream images from one client to another through IIS (or other) server

  20 avril 2012, par eselk

  I'm new to FFMPEG and maybe I should post this in their forums, but you guys here seem to know everything, so here goes. I have a client app that takes screen shots and saves them as images (256 color bitmaps currently, can change if needed), it does this at a rate of about 4 fps. I currently use my own socket code written in C# to push these to my socket server (also C#) running on a Windows 2008 server. That server then sends these images out to several clients that display them as they are received and also buffers them to allow for rewind, pause, etc, like a DVR. My current format requires approx 100KB per frame, and thus only works for a very small number of clients.

  I started looking at FFMPEG and the compression with MPEG1 and especially MPEG4 is amazing, and so is the quality. What I'm looking for is a basic guide, tutorial, or steps, to produce something similar to my current design, but using FFMPEG and actual video streaming. Ideally the player side could be something like Flash or anything that is easy to embed in a .NET WinForm (or a browser control I can host in the WinForm), and it would need to support buffering still so they can pause and rewind (about 5 or 10 mins, which seems like a lot, but remember this is only 4 fps and 256 color, about 1 or 2 MB per min in my testing).

  I see that FFMPEG, the command-line utility, and I assume the API, even has options for posting to a server via UDP or TCP, so maybe I'll use that instead of my own socket code. Ideally my app would feed images to FFMPEG library at a rate of 4fps as they come from the screen-shot unit, and it would send these up to my IIS server (or another server ?) which would then server them to client(s) that could use them similar to a YouTube video.

• How To Write An Oscilloscope

  29 avril 2012, par Multimedia Mike — General, gme, oscilloscope, visualization

  I’m trying to figure out how to write a software oscilloscope audio visualization. It’s made more frustrating by the knowledge that I am certain that I have accomplished this task before.

  In this context, the oscilloscope is used to draw the time-domain samples of an audio wave form. I have written such a plugin as part of the xine project. However, for that project, I didn’t have to write the full playback pipeline— my plugin was just handed some PCM data and drew some graphical data in response. Now I’m trying to write the entire engine in a standalone program and I’m wondering how to get it just right.

  
  
  

  This is an SDL-based oscilloscope visualizer and audio player for Game Music Emu library. My approach is to have an audio buffer that holds a second of audio (44100 stereo 16-bit samples). The player updates the visualization at 30 frames per second. The o-scope is 512 pixels wide. So, at every 1/30th second interval, the player dips into the audio buffer at position ((frame_number % 30) * 44100 / 30) and takes the first 512 stereo frames for plotting on the graph.

  It seems to be working okay, I guess. The only problem is that the A/V sync seems to be slightly misaligned. I am just wondering if this is the correct approach. Perhaps the player should be performing some slightly more complicated calculation over those (44100/30) audio frames during each update in order to obtain a more accurate graph ? I described my process to an electrical engineer friend of mine and he insisted that I needed to apply something called hysteresis to the output or I would never get accurate A/V sync in this scenario.

  Further, I know that some schools of thought on these matters require that the dots in those graphs be connected, that the scattered points simply won’t do. I guess it’s a stylistic choice.

  Still, I think I have a reasonable, workable approach here. I might just be starting the visualization 1/30th of a second too late.

• FFmpeg error - "at least one output file must be specified" [closed]

  7 février 2013, par Derrick Tucker

  I'm having a little trouble, and I feel like the solution is probably starting me in the face.

  ffmpeg -ss 0 -i rawvid.flv -t 33 -vf scale=640x480 -b:21504 test.mpg

  When run, this yells at me that "At least one output file must be specified". I've been knocking me head on the wall for hours now, what am I missing ?

  PS : FFmpeg works fine, and if I remove all of the flags in the statement above, it works.