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• MKV to MP4 command on MacOS [closed]

  28 février 2023, par Zakary Morton

  First time attempting anything more in-depth via Terminal, and I think I've sorted out the proper coding for my conversion. What I'd like to know/double-check are : 1) Is there a way to compress/control the size of the output file ? ; 2) Can I run this from a top-level folder and convert all videos under it rather than just next level down ? ; 3) Can I automate this somehow ? ; 4) Am I converting these in a way that will make them playable on apple tv ? ; 4) And finally, like, did I do it right ? Is there a simpler way to write this ?

  


  Here's the command :

  


  


  mkdir output
for f in *.mkv ; do ffmpeg -i "$f" -c:v libx265 -c:a aac -b:a 128k -preset : veryfast -tag:v hvc1 "output/$f%mkvmp4" ;done

  


  


  Seems to be running ok, but not sure how long its meant to take to complete. Thanks for your inside from a newb

  


• ffmpeg decode multiple streams at same time

  29 février 2012, par broschb

  I am using ffmpeg to decode a file and play it back on an android device. I have this working and would now like to decode two streams at the same time. I have read some comments regarding needing to use av_lockmgr_register() call with ffmpeg, unfortunately I am not sure how to use these and how the flow would work when using these locks.

  Currently I have seperate threads on the java side making requests through JNI to native code that is communicating with ffmpeg.

  Do the threads need to be on the native(NDK) side, or can I manage them on the java side ? And do I need to do any locking, and if so how does that work with ffmpeg ?

  ***UPDATE
  I have this working now, it appears that setting up the threads at the java sdk level transfers into separate threads at the native level. With that I was able to create a struct with my variables, and then pass a variable to the native layer to specify what struct to use for each video. So for I have needed to use any mutexs or locks at the native level, and haven't had any issues.

  Does anyone know of potential gotchas I may encounter by not doing so with ffmpeg ?

• avcodec/utvideodec : Avoid qsort when creating Huffman tables

  24 septembre 2020, par Andreas Rheinhardt

  avcodec/utvideodec : Avoid qsort when creating Huffman tables
  The Ut video format uses Huffman trees which are only implicitly coded
  
  in the bitstream : Only the lengths of the codes are coded, the rest has
  
  to be inferred by the decoder according to the rule that the longer
  
  codes are to the left of shorter codes in the tree and on each level the
  
  symbols are descending from left to right.
  Because longer codes are to the left of shorter codes, one needs to know
  
  how many non-leaf nodes there are on each level in order to know the
  
  code of the next left-most leaf (which belongs to the highest symbol on
  
  that level). The current code does this by sorting the entries to be
  
  ascending according to length and (for entries with the same length)
  
  ascending according to their symbols. This array is then traversed in
  
  reverse order, so that the lowest level is dealt with first, so that the
  
  number of non-leaf nodes of the next higher level is known when
  
  processing said level.
  But this can also be calculated without sorting : Simply count how many
  
  leaf nodes there are on each level. Then one can calculate the number of
  
  non-leaf nodes on each level iteratively from the lowest level upwards :
  
  It is just half the number of nodes of the level below.
  This improves performance : For the sample from ticket #4044 the amount
  
  of decicycles for one call to build_huff() decreased from 1055489 to
  
  446310 for Clang 10 and from 1080306 to 535155 for GCC 9.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/utvideo.c
  • [DH] libavcodec/utvideo.h
  • [DH] libavcodec/utvideodec.c