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• FFMPEG performance when reading directly from s3 vs local

  16 janvier 2020, par user1147070

  I have a usecase where I need to transcode a s3 file. I have two options

  Option a : Download the file to local, then run ffmpeg on it

  Option b : Provide a presigned URL as ffmpeg input eg -
  "./ffmpeg -loglevel debug -y -i "https://mybucket/key?signedParams" -threads 0 -map_chapters -1 -f mp4 -movflags faststart -map 0:0 -acodec libfdk_aac -ac 2 -ar 44100 -b:a 48k -sn -vn /output.mp4"

  I tried running both and comparing the time but I don’t see any much performance improvement in #b as compared to #a.

  I have 2 questions

  1. Is #b is better in performance than #a ? Or both of them are same ?

  2. In case of #b does ffmpeg wait for complete download and then start transcoding or it start downloading and transcoding simultaneously ?

• embed timestamps into MP4 container

  28 juin 2023, par Dmitrii Dunaev

  I have a fragmented MP4 file. It was created by recording a stream from a digital camera. Is there some way to store timestamps inside the container for later display on the web interface ?

  


• How to embed additional metadata to a video file in libavcodec (FFmpeg C source code fork)

  7 mars 2023, par leavittx

  I'm extending an existing codec (Hap) inside ffmpeg library, adding some additional stuff to it (modifying FFmpeg code in my own fork of it)

  


  One of the things I'd like to do is to store a per-file maximum encoded packet size in some global header/metadata so I can use it later while doing decoding (generally, the metadata/info to store can be arbitrary, size is just what I currently need for some specialized decoder I'm writing).

  


  I'm modifying the ffmpeg code file
https://github.com/FFmpeg/FFmpeg/blob/master/libavcodec/hapenc.c

  


  EDIT : What I'd like to achieve

  


  

  • Compute some numeric value during the encoding (namely, the maximum encoded frame size for the video - it's needed for a specialized fast decoder to not read all the frames beforehand) - that is done already

  


  • Store that value in the video file metadata (looks like it should be done on container level)

  


  


  My initial incorrect attempt :
But I don't currently see any possibility to save any info outside of a single packet being produced by hap_encode function and written to AVPacket *pkt parameter.

  


  

  1. Set dict parameter on AVCodecContext *avctx's priv_data :

  


  


      av_opt_set_int(avctx->priv_data, "max_compressed_frame_size", <size>, 0);&#xA;    av_opt_set(avctx->priv_data, "max_compressed_frame_size", "", 0);&#xA;</size>

  


  Later, while decoding av_opt_get/av_opt_get_int report non-existing key.

  


  

  2. Set various AVCodecContext *avctx fields :

  


  


      avctx->flags2 = <size>;&#xA;    avctx->extradata_size = <size>;&#xA;    avctx->ticks_per_frame = <size>;&#xA;    avctx->delay = <size>;&#xA;</size></size></size></size>

  


  They all also seem to be not preserved when doing decoding later (I get just default values from decoder's AVCodecContext)