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• FFmpeg what exactly is the filtergraph pipeline like during transcoding ?

  8 septembre 2017, par Jeff Gong

  I have been studying the source code for FFmpeg to attempt to understand its threading model and how it processes inputs. For example, when I run a command like :

  ffmpeg -i video.mp4 -s hd720 -c:v libx264 --preset medium -c:a aac -profile:v main -r 60 -f null /dev/null

  The input itself is irrelevant, but I am trying to understand how the transcoding pipeline works. In the source code, I see that the main steps occur in the functions transcode and transcode_step.

  It seems like for a single input, a single frame is read in, decoded, encoded, and written out. The process is obviously very complex but what I am really not understanding is what FFmpeg is doing when it attempts to build out a filtergraph. For example, in transcode_step of ffmpeg.c, there is the following code that happens right after an output stream has been selected :

  if (ost->filter && !ost->filter->graph->graph) {
  
      if (ifilter_has_all_input_formats(ost->filter->graph)) {
  
          ret = configure_filtergraph(ost->filter->graph);
  
          if (ret < 0) {
  
              av_log(NULL, AV_LOG_ERROR, "Error reinitializing filters!\n");
  
              return ret;
  
          }
  
      }
  
  }

  Does this only apply if I specify a specific series of filtering options to FFmpeg, like the one in this link ? For the sample command I input above, is this code still executed ?

  One last other question I had was for the case where I run an FFmpeg instance with a single input but multiple outputs (perhaps different variants for transcoding). In this scenario, does a single phase of transcode_step take in an input frame and send that frame through decoding and encoding for only a single one of the outputs ? Or does it take a frame at a time and process this frame for each of the outputs we have specified ?

• HEVC with Alpha Encoding on Windows

  14 juillet 2023, par CodeVortex

  I know, this question has been asked before, but most of the answers to them are very old.

  


  Actually, I am developing a website which uses transparent videos. So, I am using .webm format for them. However, as you know it is not possible to run .webm with transparency on Apple products. So, after researching on internet(stackoverflow etc), I found a solution that I should convert my video into a series of PNGs and then convert them into HEVC with alpha channel. However, according to the research I done, only the Apple hardware can properly encode HEVC with alpha channel.

  


  I am a newbie to these codecs and formats stuff. So, I think that I read somewhere that latest versions of FFMPEG can also encode HEVC with alpha. However, being a noob I can't figure out any way to write a command for this purpose. Being a beginner with almost non-existent skills in this field of expertise, it is nearly impossible for me to understand the documentations correctly. I also tried using shutterencoder and some other tools but failed.

  


  Although, there is a quicktime .mov solution but with that the file size becomes too large for my 10 sec video, almost 334 mb and as you know this size is too large for a animation video on a landing-page style basic website.

  


  So, now my question is there any way to properly encode HEVC with alpha on Windows or Linux to maintain transparency ?

  


  If this is not possible, then is there any other way to create such transparent videos on Windows or Linux which can be played on browsers of Apple devices ?

  


  I am stuck on this for 3 days, So, any type of help is greatly regarded. I am also providing the link to my videos, if someone wants to take a closer look on codes and formats of these videos : Videos Link

  


  P.S : if anyone with a mac device can encode these transparent videos for me, then that would be best and I shall be very grateful to you

  


• lavc/vvc : Ensure subpictures don't overlap

  22 février, par Frank Plowman

  lavc/vvc : Ensure subpictures don't overlap
  This is essentially a re-implementation of
  
  https://patchwork.ffmpeg.org/project/ffmpeg/patch/20241005223955.54158-1-post@frankplowman.com/
  That patch was not applied last time.  Instead we opted to identify
  
  issues which could be caused by invalid subpicture layouts and remedy
  
  those issues where they manifest, either through error detection or code
  
  hardening.  This was primarily implemented in the set
  
  https://patchwork.ffmpeg.org/project/ffmpeg/list/?series=13381.
  This has worked to some degree, however issues with subpicture layouts
  
  continue to crop up from the fuzzer and I've fixed a number of bugs
  
  related to subpicture layouts since then.  I think it's best to return
  
  to the initial plan and simply check if the subpicture layout is valid
  
  initially.
  This implementation is also lighter than the first time — by doing a
  
  bit more logic in pps_subpic_less_than_one_tile_slice, we are able to
  
  store a tile_in_subpic map rather than a ctu_in_subpic map.  This
  
  reduces the size of the map to the point it becomes possible to allocate
  
  it on the stack.  Similar to 8bd66a8c9587af61c7b46558be3c4ee317c1af5a,
  
  the layout is also validated in the slice map construction code, rather
  
  than in the CBS, which avoids duplicating some logic.
  Signed-off-by : Frank Plowman <post@frankplowman.com>
  

  • [DH] libavcodec/vvc/ps.c