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• aacenc_pred : rework the way prediction is done

  29 août 2015, par Rostislav Pehlivanov

  aacenc_pred : rework the way prediction is done
  This commit completely alters the algorithm of prediction.
  
  The original commit which introduced prediction was completely
  
  incorrect to even remotely care about what the actual coefficients
  
  contain or whether any options were enabled. Not my actual fault.
  This commit treats prediction the way the decoder does and expects
  
  to do : like lossy encryption. Everything related to prediction now
  
  happens at the very end but just before quantization and encoding
  
  of coefficients. On the decoder side, prediction happens before
  
  anything has had a chance to even access the coefficients.
  Also the original implementation had problems because it actually
  
  touched the band_type of special bands which already had their
  
  scalefactor indices marked and it’s a wonder the asserion wasn’t
  
  triggered when transmitting those.
  Overall, this now drastically increases audio quality and you should
  
  think about enabling it if you don’t plan on playing anything encoded
  
  on really old low power ultra-embedded devices since they might not
  
  support decoding of prediction or AAC-Main. Though the specifications
  
  were written ages ago and as times change so do the FLOPS.
  Signed-off-by : Rostislav Pehlivanov <atomnuker@gmail.com>
  

  • [DH] libavcodec/aac.h
  • [DH] libavcodec/aaccoder.c
  • [DH] libavcodec/aacenc.c
  • [DH] libavcodec/aacenc.h
  • [DH] libavcodec/aacenc_pred.c
  • [DH] libavcodec/aacenc_pred.h

• ffmpeg generated video with silent audio has different stream lengths

  18 septembre 2015, par JennHarper

  I am trying to generate a video clip of a single image and add a silent audio track for concatenating with other video files.
  I can successfully create the mp4 video with the desired image and audio track BUT, according to mediaInfo, the length of the video stream and the length of the audio stream are different. They are off by up to 60 ms. As I plan to concatenate several of these image clips and other video clips, I don’t want the error to accumulate. Any thoughts or suggestions for maintaining perfect video/audio sync ?

  Here are the ffmpeg commands that I am using :

  C :\FFmpeg\bin\ffmpeg.exe -loop 1 -i myImage.jpg -codec:v libx264 -t 7 -profile:v high -preset slow -r 25 -b:v 500k -maxrate 500k -vf scale=1280:720 -y videoStreamOnly.mp4

  C :\FFmpeg\bin\ffmpeg.exe -f lavfi -i anullsrc=r=48000 -i videoStreamOnly.mp4 -shortest -c:v copy -c:a aac -strict experimental -y videoWithSilentAudioStream.mp4

• how to trim video in h264 format using ffmpeg while preserving quality ?

  16 décembre 2020, par prisonmike11

  I'm new to ffmpeg,

  


  I'm trimming a small clip from a bluray H264 video by providing start and end duration.

  


  I tried :

  


  ffmpeg -ss 00:01:00 -i input.mp4 -to 00:02:00 -c copy output.mp4


  


  but this results in stuttering issues in start of the video. The audio and video also don't match.

  


  I tried using -c libx264 but this is taking too long and the output video has much lower bit rate.

  


  My goal is to trim as fast as possible while preserving quality. I don't care about the frame accuracy of the trim. I plan on uploading the output to youtube.

  


  what flags should I use ?