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• avcodec/bitstream : Consistently treat symbol as VLC_TYPE

  26 octobre 2020, par Andreas Rheinhardt

  avcodec/bitstream : Consistently treat symbol as VLC_TYPE
  If a static VLC table gets initialized a second time (or concurrently by
  
  two threads) and if said VLC table uses symbols that have the sign bit
  
  of VLC_TYPE (a typedef for int16_t) set, initializing the VLC fails. The
  
  reason is that the type of the symbol in the temporary array is an
  
  uint16_t and so comparing it to the symbol read from the VLC table will
  
  fail, because only the lower 16bits coincide. Said failure triggers an
  
  assert.
  Reviewed-by : Lynne <dev@lynne.ee>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/bitstream.c

• avcodec/smacker : Use unsigned for prediction values

  26 juin 2020, par Andreas Rheinhardt

  avcodec/smacker : Use unsigned for prediction values
  Up until now, the Smacker decoder has pretended that the prediction
  
  values are signed in code like 'pred[0] += (unsigned)sign_extend(val, 16)'
  
  (the cast has been added to this code later to fix undefined behaviour).
  
  This has been even done in case the PCM format is u8.
  Yet in case of 8/16 bit samples, only the lower 8/16 bit of the predicition
  
  values are ever used, so one can just as well just use unsigned and
  
  remove the sign extensions. This is what this commit does.
  For GCC 9 the time for one call to smka_decode_frame() for the sample from
  
  ticket #2425 decreased from 1709043 to 1693619 decicycles ; for Clang 9
  
  it went up from 1355273 to 1369089 decicycles.
  Reviewed-by : Paul B Mahol <onemda@gmail.com>
  
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@gmail.com>
  

  • [DH] libavcodec/smacker.c

• Trouble automating concatination (merging) of VOB files from DVD with FFMPEG

  2 juillet 2020, par Randy

  I have a library of decrypted DVDs, which all have their video in a series of VOB files within the usual VIDEO_TS folder. I wondered if I could use FFMPEG to combine them into a single MPEG files. So first I found this (this assumes 2 VOB files) from an old non-stack exchange post, and it works...

  


  ffmpeg -i "concat:VTS_01_1.VOB|VTS_01_2.VOB" -f DVD 


  


  ffmpeg complains sometimes about possible missing timestamps, but I've not seen any issues in the video, audio, or synchronization. This works too with slightly different complaints

  


  ffmpeg -i "concat:VTS_01_1.VOB|VTS_01_2.VOB" -f mpeg -c copy output.mpeg


  


  So what I'd like to do is make a windows (1) batch file to create the "concat" string, after analyzing a TS_VIDEO directory. Well as it turns out, putting a "|" character in a string is a tall order. (even escaping it doesn't works as expected.) So I looked up the ffmpeg docs on the "concat" subject, and they suggest using a list of files stored in a text file, like this...

  


  file 'VTS_01_1.VOB'
file 'VTS_01_2.VOB' (etc...)

  


  Then using a call to FFMPEG like this...

  


  ffmpeg -f concat -safe 0 -i mylist.txt -c copy output.mpg


  


  Well I tried that and it didn't work very well. After the first VOB file, I was getting continuous warnings about buffer underflow and time stamps, and the usually fast concatenation process slowed to a creep. Warnings typically looked like this...

  


  


  [mpeg @ 00000185e32b4200] buffer underflow st=1 bufi=1466 size=1998

  


  [mpeg @ 00000185e32b4200] Non-monotonous DTS in output stream 0:1 ;
previous : 328415794, current : 9265348 ; changing to 328415795. This may
result in incorrect timestamps in the output file.

  


  


  So can anyone suggest a method that WORKS as well as my first example, but taking the list of files from an input text file ?