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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 ?

• problem compiling ffmpeg for iFrameExtractor

  11 septembre 2012, par Robin Rye

  I'm trying to compile the ffmpeg by using the make and build files in iFrameExtractor example. firstly i tried to follow the readme file on the github, which only says to run the ./build_universal in ffmpeg folder. it did not work

  i then tried to follow the info in INSTALL without success. i then tried doing the stuff in INSTALL followed by the ./build_universal which didn't work. All the *.a files that are imported to the project exists until the end of the build sequence. when the lipo commands in build_universal are run, which i guess concat the .a files for the different architectures(?). anyhow these leave the following errors :

  lipo: specifed architecture type (armv6) for file (armv6/libavcodec.a) does not match it's cputype (16777223) and cpusubtype (3) (should be cputype (12) and cpusubtype (6))
  
  lipo: specifed architecture type (armv6) for file (armv6/libavdevice.a) does not match it's cputype (16777223) and cpusubtype (3) (should be cputype (12) and cpusubtype (6))
  
  lipo: specifed architecture type (armv6) for file (armv6/libavformat.a) does not match it's cputype (16777223) and cpusubtype (3) (should be cputype (12) and cpusubtype (6))
  
  lipo: specifed architecture type (armv6) for file (armv6/libavutil.a) does not match it's cputype (16777223) and cpusubtype (3) (should be cputype (12) and cpusubtype (6))
  
  lipo: specifed architecture type (armv6) for file (armv6/libswscale.a) does not match it's cputype (16777223) and cpusubtype (3) (should be cputype (12) and cpusubtype (6))

  i can get the project to compile for simulator if i only use ./build_armv7 but if i run the universal the .a files are removed in the end. and only using doesn't work to build for iphone 4 .

• What is the bitrate of my audio file based on ffmpeg output ?

  21 avril 2015, par blueether

  Is it the 40kb/s under Format, or is it the 16kb/s under Stream ? What is the relationship between the Format and the Stream ?
  The below output is for a file generated using Core Audio on an iphone, with an Audio Unit. The output format was specified by an AudioStreamBasicDescription descriptor

  Updated :
  Output from ffprobe -v error -show_format -show_streams 123_1429602551009.051025.m4a :

  [STREAM]
  
  index=0
  
  codec_name=aac
  
  codec_long_name=AAC (Advanced Audio Coding)
  
  profile=LC
  
  codec_type=audio
  
  codec_time_base=1/8000
  
  codec_tag_string=mp4a
  
  codec_tag=0x6134706d
  
  sample_fmt=fltp
  
  sample_rate=8000
  
  channels=1
  
  channel_layout=mono
  
  bits_per_sample=0
  
  id=N/A
  
  r_frame_rate=0/0
  
  avg_frame_rate=0/0
  
  time_base=1/8000
  
  start_pts=0
  
  start_time=0.000000
  
  duration_ts=43008
  
  duration=5.376000
  
  bit_rate=16501
  
  max_bit_rate=N/A
  
  bits_per_raw_sample=N/A
  
  nb_frames=42
  
  nb_read_frames=N/A
  
  nb_read_packets=N/A
  
  DISPOSITION:default=1
  
  DISPOSITION:dub=0
  
  DISPOSITION:original=0
  
  DISPOSITION:comment=0
  
  DISPOSITION:lyrics=0
  
  DISPOSITION:karaoke=0
  
  DISPOSITION:forced=0
  
  DISPOSITION:hearing_impaired=0
  
  DISPOSITION:visual_impaired=0
  
  DISPOSITION:clean_effects=0
  
  DISPOSITION:attached_pic=0
  
  TAG:creation_time=1970-04-16 22:36:01
  
  TAG:language=eng
  
  [/STREAM]
  
  [FORMAT]
  
  filename=123_1429602551009.051025.m4a
  
  nb_streams=1
  
  nb_programs=0
  
  format_name=mov,mp4,m4a,3gp,3g2,mj2
  
  format_long_name=QuickTime / MOV
  
  start_time=0.000000
  
  duration=5.376000
  
  size=27473
  
  bit_rate=40882
  
  probe_score=100
  
  TAG:major_brand=M4A
  
  TAG:minor_version=0
  
  TAG:compatible_brands=M4A mp42isom
  
  TAG:creation_time=1970-04-16 22:36:01
  
  TAG:iTunSMPB= 00000000 00000840 00000361 0000000000009C5F 00000000 00000000 00000000 00000000 00000000 00000000 00000000 00000000
  
  [/FORMAT]