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• x264 Decoding time increases with zerolatency

  13 avril 2016, par Ajay Ponna Venkatesh

  Reference - Why sliced thread affect so much on realtime encoding using ffmpeg x264 ?

  With Zerolatency / sliced-threads enabled, I am observing that the decoding time shoots up ! I am encoding on my Windows 10 laptop and streaming to Samsung S4 phone where it is decoded and rendered. If usually, decoding takes 2-3 ms, it shoots up to around 25 ms if I use sliced-threads. It is a real time streaming application so I need low latency and that’s why I enabled zerolatency. Can someone help please ?

  I am using the hardware decoder on the phone.

• Is there a way to check the resolution of a file in FFMPEG ? [duplicate]

  2 avril 2020, par Kaxemer

  I'm gathering some videos that I want to concatenate together. However, these videos are coming from different sources and might have different resolutions. Is there a way I can check what resolution they would be in FFMPEG programmatically ? I know that you cannot concatenate videos with different resolutions, so I want to be able to make the videos match the biggest resolution before concatenation.

  


• How does mp4 block matching work

  19 juin 2019, par YAHsaves

  I’ve been working on a video encoder that uses block matching to find similar blocks on previous frames.

  For the sake of simplicity I’ll leave out most of the details, but I’m wondering if I got the block matching algorithm right.

  In order to find a block on a previous frame my encoder uses the mean squared algorithm for the Y channel in YUV color space.

  This works by comparing each pixel of the block we want to match, with the block on the previous frame. It takes the difference of each pixel and squares it.

  After all the pixels are compared the block that has the least average difference is chosen as the desired block.

  Now this is where I need help. My encoder looks at every possible block in a 256x256 area and uses half pixel searches as well. The smallest block size it can use is 4x4.

  From what I’ve read online this is the same things mp4 uses.

  However I can’t find nearly as many blocks as mp4 appears to be able to find.

  For example here are 2 frames I want to compress. The first will be the I frame and the second is the P frame :

  

  Now after my encoder has run it is able to reduce the second frame by 80% and, what it can’t match close enough it saves as "difference" blocks. Which are grey blocks only recording the difference. They look like this :

  

  Now what I don’t get is to save these "difference" blocks as a jpg takes roughly 90kb to be accurate enough.

  Multiply that by 24 (24 frames per second) you get 2070kb per second. That’s not including how much space the actual motion vectors take up or anything else.

  However somehow mp4 is able to compress the video of the images above into a mere 700kb per second and still look better than my encoder at much larger data amounts.

  Why is this ? Is there something I’m doing wrong when looking for blocks ? Any help would be much appreciated.