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• ffmpeg/libav easy way to set options for muxer, codec, format, etc [closed]

  14 mars 2023, par Patrick

  Edit (shorter question) :

  


  In the ff tools (e.g. ffplay) I can set all kinds of options by simply providing a list of arguments in cmd. Id like to do that programmatically as well and without having to look up where it belongs and insert it in the different AVDictionary by hand every time. Is there a way to do this easily ?

  


  Long question :

  


  I recently messed around with ffplay code to see how it works and I noticed it uses a very straight forward way to parse and set all the command line options using the library internal cmdutils.h. I personally find the av_opt_set used in other examples of av wrappers quite confusing (Some args are explicitly stored in the struct, some in priv_data ? Im allowed/supposed to modify void*priv_data ? Which objects can I use av_opt_set on ? Which args go in which object and are they declared or in priv_data ? Where is this documented ?).
In ffplay all args are simply stored in an array and distributed to the right codec/muxer/format instance using cmdutil.
Id like to have exactly this functionality for my program (so that i can simply read a json config and don't need to care about it any further). Apparently the necessary OptionDef arrays are already defined in different implementation files.

  


  However my actual question : I noticed the OptionDef array definition in ffplay does not contain all options (only some from cmdutil included via macro). But other options e.g. fflags are not included anywhere (only defined somewhere else) and yet they work. So how does cmdutil set/parse them ?

  


  I hope someone can answer this, since simply adapting cmdutil would be a quite simple solution for me. Id also really appreciate some general guidance regarding my previous questions.

  


  Many Thanks in advance !

  


  I tried looking into the ffmpeg source and expected all OptionDef array definitions to be connected/collected inside a single array such that cmdutil can parse them easily. However this isn't the case and still some cmd options work. Therefore Im confused on how cmtutil is able to parse them

  


• ffmpeg/libav easy way to set options

  13 mars 2023, par Patrick

  I recently messed around with ffplay code to see how it works and I noticed it uses a very straight forward way to parse and set all the command line options using the library internal cmdutils.h. I personally find the av_opt_set used in other examples of av wrappers quite confusing (Some args are explicitly stored in the struct, some in priv_data ? Im allowed/supposed to modify void*priv_data ? Which objects can I use av_opt_set on ? Which args go in which object and are they declared or in priv_data ? Where is this documented ?).
In ffplay all args are simply stored in an array and distributed to the right codec/muxer/format instance using cmdutil.
Id like to have exactly this functionality for my program (so that i can simply read a json config and don't need to care about it any further). Apparently the necessary OptionDef arrays are already defined in different implementation files.

  


  However my actual question : I noticed the OptionDef array definition in ffplay does not contain all options (only some from cmdutil included via macro). But other options e.g. fflags are not included anywhere (only defined somewhere else) and yet they work. So how does cmdutil set/parse them ?

  


  I hope someone can answer this, since simply adapting cmdutil would be a quite simple solution for me. Id also really appreciate some general guidance regarding my previous questions.

  


  Many Thanks in advance !

  


  I tried looking into the ffmpeg source and expected all OptionDef array definitions to be connected/collected inside a single array such that cmdutil can parse them easily. However this isn't the case and still some cmd options work. Therefore Im confused on how cmtutil is able to parse them

  


• How to see default NVENC hevc options in ffmpeg

  18 mars 2023, par Ivan Gorin

  I am trying to use the hevc_nvenc encoder in ffmpeg to reencode an old video I have. Obviously software encoding using libx265 would be better, but I want to make in fast. I am trying to optimize for video quality, so I am using these options :

  


  -profile:v main -b_ref_mode 0 -preset p7 -tune hq -rc vbr


  


  b_ref_mode 0 since my gpu doesn't support bframe reference mode.

  


  This gives results with average bitrate of around 2M, so I am guessing that is the default bitrate setting for nvenc. Increasing -b:v increases average bitrate, but around 6.5M it stops. Even using -b:v 50M gives the same video bitrate. I have also tried setting -cq 1 to force the best quality possible, but that actually decreases bitrate to around 4.5M. The only way I found to get the desired bitrate is using -cq 1 and -maxrate set to a big value. This removes the restriction, and actually the -b:v option is no longer needed, it seems like it doesn't have any effect at all.

  


  All of this behaviour seems very strange to me, with some hidden default values for bitrate and maxrate, so the question is where can I see these values ? I tried using ffmpeg with -loglevel debug but didn't see these values getting passed, and the documentation I found says maxrate default in ffmpeg is 0 (what does this mean ?).