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• ffmpeg quality conversion options (video compression)

  25 septembre 2020, par Jason Hunter

  Can you provide a link, or an explanation, to the -q:v 1 argument that deals with video/image quality, and compression, in ffmpeg.

  


  Let me explain...

  


  for f in *
   do 
     extension="${f##*.}"
     filename="${f%.*}"
     ffmpeg -i "$f" -q:v 1 "$filename"_lq."$extension"
     rm -f "$f"
   done


  


  The ffmpeg for loop above compresses all images and videos in your working directory, it basically lowers the quality which results in smaller file sizes (the desired outcome).

  


  I'm most interested in the -q:v 1 argument of this for loop. The 1 in the -q:v 1 argument is what controls the amount of compression. But I can't find any documentation describing how to change this value of 1, and describing what it does. Is it a percentage ? Multiplier ? How do I adjust this knob ? Can/should I use negative values ? Integers only ? Min/max values ? etc.

  


  I started with the official documentation but the best I could find was a section on video quality, and the -q flag description is sparse.

  


  


  -frames[:stream_specifier] framecount (output,per-stream)
  
Stop writing to the stream after framecount frames.
  
.
  
-q[:stream_specifier] q (output,per-stream)
  

  
-qscale[:stream_specifier] q (output,per-stream)
  
Use fixed quality scale (VBR). The meaning of q/qscale is codec-dependent. If qscale is used without a stream_specifier then it applies only to the video stream, this is to maintain compatibility with previous behavior and as specifying the same codec specific value to 2 different codecs that is audio and video generally is not what is intended when no stream_specifier is used.

  


  


• ffmpeg hevc decoding fail [android]

  8 mars 2016, par revannen

  I am trying to decode h.265 with x265 and ffmpeg library, so that I downloaded ffmpeg 2.8.6 tar and x265 1.9 ver from the official site.

  now, the problem is when I decode h.264 with
  avcodec_find_decoder(AV_CODEC_ID_H264) ;
  is totally fine. :)

  but, when I try to decode h.265 with
  avcodec_find_decoder(AV_CODEC_ID_H265) ;
  it tells lots of error log.
  like.

  I/ffmpeg(4153) : nal_unit_type : 32, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 33, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 34, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 19, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : No start code is found.

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : PPS id out of range : 0

  I/ffmpeg(4153) : Error parsing NAL unit #0.

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : PPS id out of range : 0

  I/ffmpeg(4153) : Error parsing NAL unit #0.

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : PPS id out of range : 0

  I/ffmpeg(4153) : Error parsing NAL unit #0.

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : nal_unit_type : 1, nuh_layer_id : 0temporal_id : 0

  I/ffmpeg(4153) : PPS id out of range : 0

  I/ffmpeg(4153) : Error parsing NAL unit #0.

  E/decode(4153) : [407] [idvr] Error while decoding frame ! [%d]

  E/native(4153) : FAIL......-12

  1. Is it ffmpeg error ? or x265 library error ?

  2. should I modify some configuration key value in build level ? or ffmpeg running time level ?

  3. I would like to know why ffmpeg library keep saying like "No start code is found" && "PPS id out of range" [it is occur in only 265 decoding case, not 264.]

• utvideoenc : Enable support for multiple slices and use them

  14 février 2014, par Jan Ekström

  utvideoenc : Enable support for multiple slices and use them
  The official Ut Video decoder only threads with slices, thus until
  
  now any files encoded by the libavcodec encoder have only been
  
  decodable with a single thread. The default slice count is now
  
  set to subsampled_height / 120.
  Also sets slices to 1 for the Ut Video encoder tests to keep them
  
  green.
  Signed-off-by : Derek Buitenhuis <derek.buitenhuis@gmail.com>
  

  • [DBH] libavcodec/utvideoenc.c
  • [DBH] tests/fate/utvideo.mak