Recherche avancée

Sur d’autres sites (7102)

• ffmpeg recording audio / video sync issues [closed]

  1er novembre 2022, par sling jones

  I'm using ffmpeg to record NTSC analog video on Linux Fedora 36 using a Blackmagic Intensity Pro 4K for video and a Scarlett 2i2 for audio. I'm using a TBC to avoid dropped frames and to ensure a constant S-Video Y/C framerate on the analog end.

  


  The problem I'm running into is that on playback the audio will start out relatively in sync with the video at the beginning of the captured file but will eventually run ahead of the video eventually becoming many seconds off.

  


  Nothing I do seems to change this or change the degree to which it happens. The audio and video stay in sync throughout the entire video as I'm monitoring the source so I don't understand how they can diverge so much once encoded into a digital file ?

  


  Here is the command I am using :

  


  ffmpeg -hwaccel cuda -fflags +igndts -format_code ntsc -f decklink -raw_format auto -vsync passthrough -rtbufsize 1500M -thread_queue_size 512 -i 'Intensity Pro 4K' -f pulse -rtbufsize 500M -thread_queue_size 512 -i 'Scarlett 2i2 Camera Analog Stereo' -c copy -map 0:1 -map 1:0 "/tmp/ffmpeg-raw/file-raw.avi"


  


  here's the ffprobe output from one of my files :

  


  Input #0, avi, from 'test2-raw.avi':
  Metadata:
    software        : Lavf59.33.100
  Duration: 00:11:42.87, start: 0.000000, bitrate: 169341 kb/s
  Stream #0:0: Video: rawvideo (UYVY / 0x59565955), uyvy422, 720x486, 167801 kb/s, 59.94 fps, 59.94 tbr, 59.94 tbn
  Stream #0:1: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 48000 Hz, 2 channels, s16, 1536 kb/s



  


  As you can see in my code snippet, I've been throwing things at the wall for a bit. I've tried different rtbufsizes, adding -copyts, and going through the different -vsync options. I've tried it with and without hardware acceleration ( I do have a NVIDIA card), +igdts did get rid of a warning but did not help with the sync, as did changing the thread queue sizes.

  


  OBS can do this, why can't I ?

  


• avformat : add DFPWM WAV container support

  8 mars 2022, par Jack Bruienne

  avformat : add DFPWM WAV container support
  This commit adds support for storing DFPWM audio in a WAV container.
  
  It uses the WAVEFORMATEXTENSIBLE structure, following these conventions :
  
  https://gist.github.com/MCJack123/90c24b64c8e626c7f130b57e9800962c
  
  The implementation is very simple : it just adds the GUID to the list of
  
  WAV GUIDs, and modifies the WAV muxer to always use WAVEFORMATEXTENSIBLE
  
  format with that GUID.
  This creates a standard container format for DFPWM besides raw data.
  
  It will allow users to transfer DFPWM audio in a standard container
  
  format, with the sample rate and channel count contained in the file
  
  as opposed to being an external parameter as in the raw format.
  This format is already supported in my AUKit library, which is the CC
  
  analog to libav (albeit much smaller). Support in other applications is TBD.
  Signed-off-by : Jack Bruienne <jackbruienne@gmail.com>
  

  • [DH] libavformat/riff.c
  • [DH] libavformat/riffenc.c
  • [DH] libavformat/version.h

• avcodec/hevcdec : apply H.274 film grain

  29 septembre 2021, par Niklas Haas

  avcodec/hevcdec : apply H.274 film grain
  Similar in spirit and design to 66845cffc3bbb, but slightly simpler due
  
  to the lack of interlaced frames in HEVC. See that commit for more
  
  details.
  For the seed value, since no specification for this appears to exist, I
  
  semi-arbitrarily decided to base it off the POC id alone, since there's
  
  no analog of the idr_pic_id in HEVC's I-frames. This design is stable
  
  across remuxes and seeks, but changes for adjacent frames with a period
  
  that's typically long enough not to be noticeable, which makes it
  
  satisfy all of the requirements that a film grain seed should have.
  Tested with and without threading, using a patch to insert film grain
  
  metadata artificially (for lack of real files containing film grain).
  

  • [DH] libavcodec/hevc_refs.c
  • [DH] libavcodec/hevcdec.c
  • [DH] libavcodec/hevcdec.h