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• How to extract time-accurate video segments with ffmpeg ?

  25 mai 2016, par Jim Miller

  This is not a particularly new question area around here, but I’ve tried what’s been suggested there without much luck. So, my story :

  I’ve got a hunk of 15 seconds of straight-from-the-camera.mov video out of which I want to extract a specific chunk, which I can identify by start time and stop time, in seconds. I started by trying to do what I’ll call a "copy extraction" : to get seconds 9 to 12,

  ffmpeg -i test.mov -vcodec copy -acodec copy -ss 9 -to 12 test-copy.mov

  This was a not-bad start, but there are some black frames at the beginning and end of the clip, which I can’t have — it has to be a clean edit from the original. So, I tried recoding the original into a new, trimmed clip :

  ffmpeg -i test.mov -ss 00:00:09 -t 00:00:03 test-out.mov

  This is better, but not quite : There are no longer any black frames at the beginning of the clip, but they’re still there at the end.

  After some more browsing and reading, I then suspected that the problem is that ffmpeg is having trouble finding the proper points because of a lack of keyframes in the original video. So I recoded the original video to (presumably) add keyframes, in a couple of different ways. Since I want to be able to pick video at boundaries of a second ("from 9 seconds to 12 seconds"), I tried, copying various suggestions around the web,

  ffmpeg -i test.mov -force_key_frames "expr:gte(t, n_forced)" test-forced.mp4

  and

  ffmpeg -i test.mov -g 1 test-g-inserted.mp4

  (I built these as mp4’s based on some comments about an mp4 container being needed to support the keyframe search, but I’m honestly just hacking here.) I then tried the extraction as before, but on these new videos that presumably now have keyframes in them. No luck — both seem to be about the same ; the start is OK but there are still black frames at the end. (FWIW, both test-forced.mp4 and test-g-inserted.mp4 also have trailing black frames.)

  So : I’m still stuck, and would like to not be. Any insights out there as to what I’m doing wrong ? I feel like I’m close, but I really need to get rid of those trailing black frames....

• Trolls in trouble

  6 juin 2013, par Mans — Law and liberty

  Life as a patent troll is hopefully set to get more difficult. In a memo describing patent trolls as a “drain on the American economy,” the White House this week outlined a number of steps it is taking to stem this evil tide. Chiming in, the Chief Judge of the Court of Appeals for the Federal Circuit (where patent cases are heard) in a New York Times op-ed laments the toll patent trolling is taking on the industry, and urges judges to use powers already at their disposal to make the practice less attractive. However, while certainly a step in the right direction, these measures all fail to address the more fundamental properties of the patent system allowing trolls to exist in the first place.

  System and method for patent trolling

  Most patent trolling operations comprise the same basic elements :

  1. One or more patents with broad claims.
  2. The patents of (1) acquired by an otherwise non-practising entity (troll).
  3. The entity of (2) filing numerous lawsuits alleging infringement of the patents of (1).
  4. The lawsuits of (3) targeting end users or retailers.
  5. The lawsuits of (3) listing as plaintiffs difficult to trace shell companies.

  The recent legislative actions all take aim at the latter entries in this list. In so doing, they will no doubt cripple the trolls, but the trolls will remain alive, ready to resume their wicked ways once a new loophole is found in the system.

  To kill a patent troll

  As Judge Rader and his co-authors point out in the New York Times, “the problem stems largely from the fact that, [...] trolls have an important strategic advantage over their adversaries : they don’t make anything.” This is the heart of the troll, and this is where the blow should be struck. Our weapon shall be the mightiest judicial sword of all, the Constitution.

  The United States Constitution contains (in Article I, Section 8) the foundation for the patent system (emphasis mine) :

  The Congress shall have Power [...] To promote the Progress of Science and useful Arts, by securing for limited Times to Authors and Inventors the exclusive Right to their respective Writings and Discoveries.

  Patent trolls are typically not inventors. They are merely hoarders of other people’s discarded inventions, and that allowing others to reap the benefits of an inventor’s work would somehow promote progress should be a tough argument. Indeed, it is the dissociation between investment and reward which has allowed the patent trolls to rise and prosper.

  In light of the above, the solution to the troll menace is actually strikingly simple : make patents non-transferable.

  Having the inventor retain the rights to his or her inventions (works for hire still being recognised), would render the establishment of non-practising entities, which most trolls are, virtually impossible. The original purpose of patents, to protect the investment of inventors, would remain unaffected, if not strengthened, by such a change.

  Links

  • Taking on Patent Trolls to Protect American Innovation
  • Fact Sheet : White House Task Force on High-Tech Patent Issues
  • Make Patent Trolls Pay in Court
  • Constitution of the United States

• adaptive HTTP streaming for open codecs

  14 octobre 2010, par silvia

  At this week’s FOMS in New York we had one over-arching topic that seemed to be of interest to every single participant : how to do adaptive bitrate streaming over HTTP for open codecs. On the first day, there was a general discussion about the advantages and disadvantages of adaptive HTTP (...)