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• HEVC video cutting issues using FFmpeg

  4 novembre 2017, par Dmitry Katkevich

  I need to cut videos using FFmpeg and I cannot transcode original videos (because of the performance reason). And I ran into a problem with HEVC videos from IPhone : there are glithes in the beginning of the cutted video.

  Here is how we converted videos before issue :

  ffmpeg.exe -i original.MOV -c:v copy -c:a aac -ss 4 -y good.mp4

  But for HEVC video there are glitches for 1 second in the beginning of the cutted video :

  

  Then I’ve tried to put seek option before input video :

  ffmpeg.exe -ss 4 -i original.MOV -c:v copy -c:a aac -y good.mp4

  The result seems good :

  

  After some googling it turns out that -ss option before input is faster but less accurate whereas -ss option after input and before output is slower but more accurate.

  So my questions are :

  • Why -ss option behaves differently then it is put before/after input ?

  • Is there a way to avoid glitches using output seek ffmpeg option ?

  • What does ’more/less accurate’ mean ? Does it mean that the seek may be too big or to little (bigger/less than we specified) ? How big may be this difference ?

• avcodec/h2645_sei : add support for Ambient Viewing Environment SEI

  9 janvier 2023, par Jan Ekström

  avcodec/h2645_sei : add support for Ambient Viewing Environment SEI
  Defined by H.274, this SEI message is utilized by iPhones to save
  
  the nominal ambient viewing environment for the display of recorded
  
  HDR content. The contents of the message are exposed to API users
  
  as AVFrame side data containing AVAmbientViewingEnvironment.
  As the DV RPU test sample is from an iPhone and includes Ambient
  
  Viewing Environment SEI messages, its test result gets updated.
  

  • [DH] libavcodec/h2645_sei.c
  • [DH] libavcodec/h2645_sei.h
  • [DH] tests/ref/fate/hevc-dv-rpu

• FFmpeg - selecting appropriate bitrate for VP9 encoding

  11 janvier 2018, par fastily

  I am looking to encode a 4k video shot with iPhone 6s in VP9 in the best quality possible.

  For reference, stream data of the video I would like to encode, via ffprobe :

  Duration: 00:00:10.48, start: 0.000000, bitrate: 46047 kb/s
  
      Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p(tv, bt709), 3840x2160, 45959 kb/s, 29.98 fps, 29.97 tbr, 600 tbn, 1200 tbc (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler
  
        encoder         : H.264
  
      Stream #0:1(und): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, mono, fltp, 79 kb/s (default)
  
      Metadata:
  
        creation_time   : 2017-03-13T21:12:56.000000Z
  
        handler_name    : Core Media Data Handler

  I am using the following FFmpeg commands, based on these instructions (see Best Quality (Slowest) Recommended Settings section).

  1. ffmpeg -i INPUT.mov -c:v libvpx-vp9 -pass 1 -b:v 46000K -threads 4 -speed 4 -g 9999 -an -f webm -y /dev/null
  2. ffmpeg -I INPUT.mov -c:v libvpx-vp9 -pass 2 -b:v 46000K -threads 4 -speed 0 -g 9999 -an -f webm OUTPUT.webm

  Is there a best practice to select an optimal -b:v value such that the resulting video is visually indistinguishable from the original ? I have tried values ranging from 36000K-46000K, but these result in massive files with an overall bitrate exceeding the target bitrate.

  Thanks in advance !