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• How to tell ffmpeg to skip the last NAL unit ?

  31 janvier 2023, par mqnl

  I'm new to ffmpeg and trying to use it to record a streaming video (e.g. recording YouTube streams). However, I guess sometimes due to network issues, the last NAL unit is corrupted and when I want to concat multiple videos together, the error below occurs and the process exited.

  


  [NULL @ 0x558551957ec0] Invalid NAL unit size (41974 > 39166).bitrate=12309.0kbits/s speed=21.5x
[NULL @ 0x558551957ec0] missing picture in access unit with size 39182
[concat @ 0x55855194c700] h264_mp4toannexb filter failed to receive output packet
../filelist.txt: Invalid data found when processing input


  


  So I'm wondering if there's a way to tell ffmpeg to skip the last NAL unit (or skip any invalid NAL unit) without re-encoding the entire video ? Thanks in advance !

  


• Model the loss of video codec

  10 janvier 2024, par Monaco

  I want to use a neural network to model the error loss after video encoding. The modeling process is as follows :

I use ffmpeg to encode and decode video frames. Since this process is not implemented using tensors in PyTorch and cannot compute gradients, I have to separately implement a neural network in PyTorch to enable gradient backpropagation. However, it turns out that the neural network cannot effectively learn the video encoding.

  


  I want to know if there are currently any implementations of video encoders or decoders that support backpropagation of gradients. I don't necessarily need to update the parameters of the encoder/decoder, but I want it to support gradient backpropagation so that I can use it for various tasks related to deep learning.

  


• Fun With Tablets And Amazon’s App Store

  24 décembre 2011, par Multimedia Mike — General, amazon, android, app store, cyanogenmod, ios, smurfs, tablet

  I bought an Android tablet a few months ago. It is less expensive than the best tablets but no where near the bottom end of the market. I think it’s pretty good. However, one downside is that it’s not “certified” to use Google’s official marketplace. That would seem to be somewhat limiting, however…

  Enter Amazon’s Android App Store
  Amazon got into the business of selling Android Apps some time ago. I started experimenting with this on a Nexus One phone that Google gave me. When I installed the App Store on the Android tablet and logged in, I was pleasantly surprised to see all of my Amazon apps ready for downloading onto the tablet.

  So I have an App Store for use with this Android tablet.

  Anyway, the reason I bring this up is because I managed to screw up this tablet in an unusual and humorous manner. You might be wondering if an app downloaded from the Amazon App Store requires the App Store to be present in order to run. The answer is : Oh yeah ! It works like this :

  
  
  

  This means that if — perhaps out of curiosity, for example — you login to the Amazon App Store, download an app, install it, and then subsequently log out of the App Store or uninstall it altogether, the downloaded app will decline to run until you log back into the store.

  Here’s the thing– I wanted to provide a minimal level of security for my Android tablet. At the very least, I wished to lock the Amazon App Store itself since Amazon is famously (and, let’s face it, understandably) reluctant to deliberately add any friction to their shopping processes. I.e., without any external protection app, the App Store app would allow anyone to purchase any app using my tablet.

  So I purchased App Protector Pro from the Amazon App Store and it worked quite well. By default, it also password protects against modifying any system settings as well as installing new apps.

  So, here’s where I screwed up : App Protector Pro was doing its faithful duty and I uninstalled the Amazon App Store as an experiment. Suddenly, no apps obtained from the App Store would work unless I reinstalled the App Store. Okay, fair enough, except for one thing– App Protector Pro wouldn’t run without the App Store. Well, it did, it started to, tried to, but then exited. So I couldn’t re-install the App Store :

  
  
  Oops
  

  I eventually learned how to perform a factory reset of the unit which solved the problem. And, as indicated earlier, all of my apps were available for me to re-download.

  Modding, Cyanogen-style
  Open source aficionados will likely point out that there are alternate firmware options which allow me to take control of my Android tablet in a free and open manner. Among these options is CyanogenMod. After I got stuck in the situation described above, I thought I would have to resort to such an option.

  On the plus side, researching alternative firmware options is what taught me to boot the device into a recovery mode and ultimately restore to a factory default setting. But if you’ll allow me to indulge in a mini-rant regarding accessibility of open source software : I was more than a little frustrated in trying to understand what CyanogenMod could possibly offer me. Their homepage says it’s “an aftermarket firmware”. I’m not entirely sure what that means or how it can benefit me. Fortunately, they have a full feature list linked from the front page. They are, in order : Lockscreen gestures, phone goggles, OpenVPN, incognito mode, themes support, and DSP equalizer. I can’t say that any of those really add any value for me. I’d love to know if CyanogenMod supports Google Android Market and various other Google apps (such as maps and GMail). That’s a question that I can’t seem to find the answer to.

  The themes feature opens another old wound for me. Back around 1999 when I was first getting into Linux in a serious way, I remember that themes were a big theme at the Linux User Groups I would attend. I also remember lots are online articles at the time that emphasized how highly customizable the Linux desktop was in comparison to Windows 9x. I was bothered for 2 reasons : First, I thought there were more pressing problems that needed to be addressed in Linux ; and second, none of these customization options seemed particularly straightforward ; many apparently required hours of compiling and tinkering.

  Small digression. Anyway, back to CyanogenMod, I was glad to see that they prominently display a button in order to “View Video Tour”. Ah, internet video has us so spoiled these days. I was eager to see this aftermarket firmware in action to see what it could do for me. However, the link leads to… a forum post ? The thread seems to discuss how it would be a cool idea if the community could put together a video tour. At this point, the investigation just seems bizarre. It feels like a bunch of kids doing their best to do things the grown-up way.

  Okay, sorry, rant over. I try to stay positive these days. I’m sure the CyanogenMod folks are doing great, fun, and interesting work on their project. The problems they choose to solve might lack mainstream appeal, however.

  Free iPad
  Ultimately, I recently unloaded the little Android tablet because, well… when a free iPad comes your way, lower spec tablets feel a little silly to keep around. Yeah, it’s great to play around with. Though here’s one unsettling thing I noticed about Apple’s App Store. While browsing for worthwhile games to indulge in, I noticed that they had a section for “Top Grossing Games”. This was a separate list from the “Top Apps” charts. I found the list weird for 2 reasons : 1) Why do I care which games are raking in the most cash ? How does this communicate value to me, personally ? Seriously, why would I base a purchasing decision around which vendor has earned the most money ?

  Anyway, let’s move on to reason #2 this was scary : Most of the games in this list had a price of FREE. One of them was that Capcom Smurfs game that stirred up controversy some months ago because of kids making unsupervised in-app purchases of virtual smurfberries. I tend to think that a top-grossing, free to play game is probably one that heavily encourages in-app purchases. Strange how this emerging trend actually encourages me to seek out games from the “top paid” list vs. “top free”.