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• RTSP stream escape 1 or 2 seconds in output video file

  20 février 2017, par A Sahra

  I am trying to capture RTSP video from network path (rtsp ://10.29.23.1/video) using ffmpeg framework

  When i capture the video the output video file generated with ffmpeg is very low in quality and also it escape 1 or 2 seconds after each 5 seconds of the source video

  The command that i am running is :

  >#ffmpeg -i rtsp://10.20.2.2/aerovid -vcodec libx264 -framerate 5 -f mp4 public/out.mp4
  
  Log:after running above command:
  
  [h264 @ 0x2b75640] P sub_mb_type 32 out of range at 16 1464 bitrate=226.8kbits/s dup=30 drop=0 speed=3.27x 
  
  [h264 @ 0x2b75640] error while decoding MB 16 14 
  
  [h264 @ 0x2b75640] concealing 402 DC, 402 AC, 402 MV errors in P frame 
  
  [h264 @ 0x2b75640] mb_type 52 in P slice too large at 0 379 bitrate=239.0kbits/s dup=48 drop=0 speed=1.65x 
  
  [h264 @ 0x2b75640] error while decoding MB 0 3 
  
  [h264 @ 0x2b75640] concealing 869 DC, 869 AC, 869 MV errors in P frame 
  
  [h264 @ 0x2b75640] out of range intra chroma pred mode 
  
  [h264 @ 0x2b75640] error while decoding MB 34 1 
  
  [h264 @ 0x2b75640] concealing 917 DC, 917 AC, 917 MV errors in P frame 
  
  [h264 @ 0x2b75640] P sub_mb_type 9 out of range at 9 5 
  
  [h264 @ 0x2b75640] error while decoding MB 9 5 
  
  [h264 @ 0x2b75640] concealing 778 DC, 778 AC, 778 MV errors in P frame 
  
  [h264 @ 0x2b75640] negative number of zero coeffs at 9 1507 bitrate= 288.7kbits/s dup=50 drop=0 speed=1.37x 
  
  [h264 @ 0x2b75640] error while decoding MB 9 15 
  
  [h264 @ 0x2b75640] concealing 368 DC, 368 AC, 368 MV errors in P frame 
  
  [h264 @ 0x2b75640] out of range intra chroma pred mode 
  
  [h264 @ 0x2b75640] error while decoding MB 12 3 
  
  [h264 @ 0x2b75640] concealing 857 DC, 857 AC, 857 MV errors in P frame 
  
  [h264 @ 0x2b75640] mb_type 53 in P slice too large at 38 6 
  
  [h264 @ 0x2b75640] error while decoding MB 38 6 
  
  [h264 @ 0x2b75640] concealing 708 DC, 708 AC, 708 MV errors in P frame    
  
  Invalid UE golomb code 
  
  [h264 @ 0x2b75640] cbp too large (3199971767) at 28 12 
  
  [h264 @ 0x2b75640] error while decoding MB 28 12 
  
  [h264 @ 0x2b75640] concealing 472 DC, 472 AC, 472 MV errors in P frame

  What is the reason and how to solve it please ?

• Gallery of VP8 Encoding Naivete

  15 octobre 2010, par Multimedia Mike — VP8

  I’ve been toiling away as a multimedia technology generalist for so long that it’s easy for me to forget that not everyone is as versed in the minutiae of the domain as I am. But I recently experienced what it’s like to be such an outsider when I posted about my toy VP8 encoder, expressing that it’s one of the hardest things I have ever tried to do. I heard of from number of people who do have extensive experience in video encoding, particularly with the H.264 and VP8 codecs. Their reactions were predictable : What’s so hard ? Look, you might be a little too immersed in the area to really understand a relative beginner’s perspective.

  And to all the people who suggested that I should get the encoder into FFmpeg ASAP : Are you crazy ?! Did you see what the first pass of the encoder produced ? Do you have lower standards than even I do ?

  
  
  

  Not Giving Up
  I worked a little more on the toy encoder. Remember that the above image is what I’m hoping to encode somewhat faithfully for this experiment. In my first pass, I attempted vertical prediction for all planes. For my next pass, I forced the chroma planes to mid-level (which results in a greyscale image) and played with the 16×16 luma prediction modes. When implementing an extremely naive algorithm to decide which 16×16 prediction mode would be the best for a particular block, this is what the program produced :

  
  
  

  For fun, here is what the image encodes to when forcing various prediction modes :
  

  I think the DC-only prediction mode actually looks a little better than the image that the naive algorithm produced :

  
  
  

  Vertical 16×16 prediction, similar to the image from the last post (just in black and white) :
  

  
  
  

  Horizontal 16×16 prediction :
  

  
  
  

  This is the 16×16 prediction mode unique to VP8, the TrueMotion mode (based on On2/Duck’s very first video codec) :
  

  
  
  

  Wow, these encodings really bring down the cheerful tone of the original image.

  Next Steps
  I have little reason to believe that I am encoding and subsequently reconstructing the image correctly (i.e., error is likely propagating through the entire encoding). If I have time, the next step is to validate my reconstruction against the encoder. Then I need to get the entropy considerations correct so that I actually get some compression out of this format.

• avcodec/pngdec : Fix APNG_DISPOSE_OP_BACKGROUND

  20 août 2022, par Andreas Rheinhardt

  avcodec/pngdec : Fix APNG_DISPOSE_OP_BACKGROUND
  APNG works with a single reference frame and an output frame.
  
  According to the spec, decoding APNG works by decoding
  
  the current IDAT/fdAT chunks (which decodes to a rectangular
  
  subregion of the whole image region), followed by either
  
  overwriting the region of the output frame with the newly
  
  decoded data or by blending the newly decoded data with
  
  the data from the reference frame onto the current subregion
  
  of the output frame. The remainder of the output frame
  
  is just copied from the reference frame.
  
  Then the reference frame might be left untouched
  
  (APNG_DISPOSE_OP_PREVIOUS), it might be replaced by the output
  
  frame (APNG_DISPOSE_OP_NONE) or the rectangular subregion
  
  corresponding to the just decoded frame has to be reset
  
  to black (APNG_DISPOSE_OP_BACKGROUND).
  The latter case is not handled correctly by our decoder :
  
  It only performs resetting the rectangle in the reference frame
  
  when decoding the next frame ; and since commit
  
  b593abda6c642cb0c3959752dd235c2faf66837f it does not reset
  
  the reference frame permanently, but only temporarily (i.e.
  
  it only affects decoding the frame after the frame with
  
  APNG_DISPOSE_OP_BACKGROUND). This is a problem if the
  
  frame after the APNG_DISPOSE_OP_BACKGROUND frame uses
  
  APNG_DISPOSE_OP_PREVIOUS, because then the frame after
  
  the APNG_DISPOSE_OP_PREVIOUS frame has an incorrect reference
  
  frame. (If it is not followed by an APNG_DISPOSE_OP_PREVIOUS
  
  frame, the decoder only keeps a reference to the output frame,
  
  which is ok.)
  This commit fixes this by being much closer to the spec
  
  than the earlier code : Resetting the background is no longer
  
  postponed until the next frame ; instead it is applied to
  
  the reference frame.
  Fixes ticket #9602.
  (For multithreaded decoding it was actually already broken
  
  since commit 5663301560d77486c7f7c03c1aa5f542fab23c24.)
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavcodec/pngdec.c