Recherche avancée

Sur d’autres sites (3057)

• How can I mux (or encapsulate) H.264 RTP output into a container using FFMPEG ?

  7 octobre 2013, par Grad

  I am working on the effects of network losses in video transmission. In order to simulate the network losses I use a simple program which drops random RTP packets from the output of H.264 RTP encoding.

  I use Joint Model (JM) 14.2 in order to encode the video. However, I don't use AnnexB format as my output, instead I choose the output as RTP packets. The JM output is generated as RTP packets with RTP headers and payload as a sequence. After that, some of RTP packets are dropped by using a simple program. Then, I can decode the output bitstream by using also JM and it's error concealment methods.

  The main purpose of this process is to evaluate the differences created by network losses on the human video quality perception. In order to measure the perceived quality, the shown video must be in its decoded form (i.e. full resolution) or it can be decodable at the receiver side. The RTP packets created by the JM Encoder cannot be decoded without the JM software installed. However, with the proper header (or container) most video players are able to decode the bitstream. So, the my goal in this question is to encapsulate my encoded RTP packet bitstream in a common container such as AVI or MP4 to have my content decodable at the receiver computer.

  The format of the encoded bitstream in RTP packetized form is as follows :

       ----------------------------------------------------------------------
  
       | RTP Header #1 | RTP Payload #1 | RTP Header #2 | RTP Payload #2 |...
  
       ----------------------------------------------------------------------

  In order to find the video quality, I want to make a subjective test with these bitstreams. I can make these test by using the full resolution data decoded by myself whereas it's very inconvenient to crowdsource this subjective test with GBs of video data on the Internet. So, I want to mux these bitstreams into a container (i.e. AVI) by using FFMPEG. I have tried to decode these bitstreams with FFMPEG and FFPLAY ; however, both of them didn't work. I also tried the following command and it didn't work, either.

      ffmpeg - f h264 -i  -vcodec copy -r 25 out.avi

  Which format or muxer should I use ? Do I need to convert these files to any other format ?

• What Every Programmer Should Know

  24 décembre 2012, par Multimedia Mike — General

  During my recent effort to force myself to understand Unicode and modern text encoding/processing, I was reminded that this is something that “every programmer should just know”, an idea that comes up every so often, usually in relation to a subject in which the speaker is already an expert. One of the most absurd examples I ever witnessed was a blog post along the lines of “What every working programmer ought to know about [some very specific niche of enterprise-level Java programming]“. I remember reading through the article and recognizing that I had almost no knowledge of the material. Disturbing, since I am demonstrably a “working programmer”.

  For fun, I queried the googles on the matter of what ever programmer ought to know.

  Specific Topics
  Here is what every programmer should know about : Unicode, time, memory (simple), memory (extremely in-depth), regular expressions, search engine optimization, floating point, security, basic number theory, race conditions, managed C++, VIM commands, distributed systems, object-oriented design, latency numbers, rate monotonic algorithm, merging branches in Mercurial, classes of algorithms, and human names.

  Broader Topics
  20 subjects every programmer should know, 97 things every programmer should know, 12 things every programmer should know, things every programmer should know (27 items), 10 papers every programmer should read at least twice, 10 things every programmer should know for their first job.

  Meanwhile, I remain fond of this xkcd comic whose mouseover text describes all that a person genuinely needs to know. Still, the new year is upon us, a time when people often make commitments to bettering themselves, and it couldn’t hurt (much) to at least skim some of the lists and find out what you never knew that you never knew.

  What About Multimedia ?
  Reading the foregoing (or the titles of the foregoing pieces), I naturally wonder if I should write something about what every programmer should know about multimedia. I think it would look something like a multimedia programming FAQ. These are some items that I can think of :

  1. YUV : The other colorspace (since most programmers are only familiar with RGB and have no idea what to make of the YUV that comes out of most video decoding APIs)
  2. Why you can’t easily seek randomly to any specific frame in a video file (keyframe/interframe discussion and their implications)
  3. Understand your platform before endeavoring to implement multimedia software (modern platforms, particularly mobile platforms, probably provide everything you need in the native APIs and there is likely little reason to compile libavcodec for the platform)
  4. Difference between containers and codecs (longstanding item, but I would argue it’s less relevant these days due to standardization on the MPEG — MP4/H.264/AAC — stack)
  5. What counts as a multimedia standard in this day and age (comparing the foregoing MPEG stack with the WebM/VP8/Vorbis stack)
  6. Trade-offs to consider when engineering a multimedia solution
  7. Optimization doesn’t always work the way you think it does (not everything touted as a massive speed-up in the world of computing — whether it be multithreaded CPUs, GPGPUs, new SIMD instruction sets — will necessarily be applicable to multimedia processing)
  8. A practical guide to legal issues would not be amiss
  9.  ???

  What other items count as “something multimedia-related that every programmer should know” ?

• Python remove and change video background [closed]

  21 juillet 2022, par Billi Alt

  I have a video with a human in the foreground and a white wall in the background. I would like to remove the white wall and to add several background videos. So one video would be from second 0-5 the next from 5-20 and so on. And the end video should still have the initial audio. Do you have any idea how to do that in python ?