Recherche avancée

Sur d’autres sites (13513)

• AAC encoder : Extensive improvements

  11 octobre 2015, par Claudio Freire

  AAC encoder : Extensive improvements
  This finalizes merging of the work in the patches in ticket #2686.
  Improvements to twoloop and RC logic are extensive.
  The non-exhaustive list of twoloop improvments includes :
  
   - Tweaks to distortion limits on the RD optimization phase of twoloop
  
   - Deeper search in twoloop
  
   - PNS information marking to let twoloop decide when to use it
  
     (turned out having the decision made separately wasn’t working)
  
   - Tonal band detection and priorization
  
   - Better band energy conservation rules
  
   - Strict hole avoidance
  For rate control :
  
   - Use psymodel’s bit allocation to allow proper use of the bit
  
     reservoir. Don’t work against the bit reservoir by moving lambda
  
     in the opposite direction when psymodel decides to allocate more/less
  
     bits to a frame.
  
   - Retry the encode if the effective rate lies outside a reasonable
  
     margin of psymodel’s allocation or the selected ABR.
  
   - Log average lambda at the end. Useful info for everyone, but especially
  
     for tuning of the various encoder constants that relate to lambda
  
     feedback.
  Psy :
  
   - Do not apply lowpass with a FIR filter, instead just let the coder
  
     zero bands above the cutoff. The FIR filter induces group delay,
  
     and while zeroing bands causes ripple, it’s lost in the quantization
  
     noise.
  
   - Experimental VBR bit allocation code
  
   - Tweak automatic lowpass filter threshold to maximize audio bandwidth
  
     at all bitrates while still providing acceptable, stable quality.
  I/S :
  
   - Phase decision fixes. Unrelated to #2686, but the bugs only surfaced
  
     when the merge was finalized. Measure I/S band energy accounting for
  
     phase, and prevent I/S and M/S from being applied both.
  PNS :
  
   - Avoid marking short bands with PNS when they’re part of a window
  
     group in which there’s a large variation of energy from one window
  
     to the next. PNS can’t preserve those and the effect is extremely
  
     noticeable.
  M/S :
  
   - Implement BMLD protection similar to the specified in
  
     ISO-IEC/13818:7-2003, Appendix C Section 6.1. Since M/S decision
  
     doesn’t conform to section 6.1, a different method had to be
  
     implemented, but should provide equivalent protection.
  
   - Move the decision logic closer to the method specified in
  
     ISO-IEC/13818:7-2003, Appendix C Section 6.1. Specifically,
  
     make sure M/S needs less bits than dual stereo.
  
   - Don’t apply M/S in bands that are using I/S
  Now, this of course needed adjustments in the compare targets and
  
  fuzz factors of the AAC encoder’s fate tests, but if wondering why
  
  the targets go up (more distortion), consider the previous coder
  
  was using too many bits on LF content (far more than required by
  
  psy), and thus those signals will now be more distorted, not less.
  The extra distortion isn’t audible though, I carried extensive
  
  ABX testing to make sure.
  A very similar patch was also extensively tested by Kamendo2 in
  
  the context of #2686.
  

  • [DH] Changelog
  • [DH] libavcodec/aac.h
  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aaccoder_trellis.h
  • [DH] libavcodec/aaccoder_twoloop.h
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h
  • [DH] libavcodec/aacenc_is.c
  • [DH] libavcodec/aacenc_is.h
  • [DH] libavcodec/aacenc_pred.c
  • [DH] libavcodec/aacenc_quantization.h
  • [DH] libavcodec/aacenc_utils.h
  • [DH] libavcodec/aacpsy.c
  • [DH] libavcodec/mathops.h
  • [DH] libavcodec/mips/aaccoder_mips.c
  • [DH] libavcodec/psymodel.c
  • [DH] libavcodec/psymodel.h
  • [DH] tests/fate/aac.mak

• What are the correct conversion steps to generate a video from PDF with ffmpeg and mp4box

  25 juin 2020, par Michael Rall

  I need to convert a PDF-Document to a DASH-compatible stream. Every page of the PDF should be displayed for one second. Quality should be rather good, so that text and line graphics can still be read clearly. Additionally I want to be able to seek every page, so keyframes(?) should be (exactly) every second.

  


  Im using poppler-tools to extract the pdf-pages as png's -> works

  


  Im using ffmpeg to convert the single images to an x264 encoded mp4 video -> works (but maybe problematic)

  


  string.Format("-r 1 -i \"{0}.page_%d.png\" -r 24 -vcodec libx264 -pix_fmt yuv420p {0}.output.mp4", basePath)


  


  Im using MP4Box to convert that video to dash -> works (but needs improvement)

  


  string.Format("-dash 1000 -frag 1000 -rap -segment-name {1}_dash_$RepresentationID$_$Number$ -url-template {0}.output.mp4 -out \"{0}.{2}\"", basePath, tempDataId, STREAM_MANIFEST_FILE_POSTFIX)


  


  Now I have 2 Problems/Questions

  


  

  1. Are the settings for framerate, quality, outputformat correct for the goals I want to achieve

  


  2. When displaying the resulting DASH-Stream in the Demo-Player from https://github.com/Dash-Industry-Forum/dash.js/wiki it plays the stream, but as soon as I try to seek the player starts loading forever. Setting the position to start and let it play again works. The network tab in my browser-debugger shows that the player tries to load the segments and gets them successfully.

  


  


  I guess its a problem with keyframes, fragments or similar. Can somebody correct my conversion steps ?

  


  kind regards

  


• Unknown Encoder error when using libx264 with FFMPEG

  9 juillet 2018, par newuser

  I have followed the guide given here. And everything goes smoothly. But when I try to run a command with FFMPEG to convert to H.264. I get the error : Unknown Encoder ’libx264’
  I’m on Ubuntu 16.04 LTS.