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• When creating a Xing or Info tag in an MP3, may I use any MP3 header or does it have to match other frames ?

  13 décembre 2019, par Alexis Wilke

  I have a set of bare MP3 files. Bare as in I removed all tags (no ID3, no Xing, no Info) from those files.

  Just before sending one of these files to the client, I want to add an Info tag. All of my files are CBR so we will use an Info tag (no Xing).

  Right now I get the first 4 bytes of the existing MP3 to get the Version (MPEG-1, Layer III), Bitrate, Frequency, Stereo Mode, etc. and thus determine the size of one frame. I create the tag that way, reusing these 4 bytes for the Info tag and determining the size of the frame.

  For those wondering, these 4 bytes may look like this :

  FF FB 78 04

  To me it felt like you are expected to use the exact same first 4 bytes in the Info tag as found in the other audio frames of the MP3, but when using ffmpeg, they stick an Info tag with a hard coded header (wrong bitrate, wrong frequency, etc.)

  My question is : Is ffmpeg really doing it right ? (LAME doesn’t do that) Could I do the same, skipping the load of the first 4 bytes and still have the greater majority of the players out there play my files as expected ?

  Note : since I read these 4 bytes over the network, it would definitely save a lot of time and some bandwidth to not have to load these 4 bytes on a HEAD request. Resources I could use for the GET requests instead...

• avcodec/simple_idct_template : change the idct coefficients so that they match the...

  12 janvier 2014, par Michael Niedermayer

  avcodec/simple_idct_template : change the idct coefficients so that they match the x86 code
  no changes in either standard deviation or PSNR is seen in any of the changed fate
  
  cases
  MSE changes from 0.05012422 to 0.04890000
  Signed-off-by : Michael Niedermayer <michaelni@gmx.at>
  

  • [DH] libavcodec/simple_idct_template.c
  • [DH] tests/ref/fate/prores-422
  • [DH] tests/ref/fate/prores-422_hq
  • [DH] tests/ref/fate/prores-422_lt
  • [DH] tests/ref/fate/prores-422_proxy
  • [DH] tests/ref/fate/prores-alpha
  • [DH] tests/ref/fate/prores-alpha_skip
  • [DH] tests/ref/fate/prores-transparency
  • [DH] tests/ref/fate/prores-transparency_skip
  • [DH] tests/ref/vsynth/vsynth1-dnxhd-720p-10bit
  • [DH] tests/ref/vsynth/vsynth1-prores
  • [DH] tests/ref/vsynth/vsynth1-prores_ks
  • [DH] tests/ref/vsynth/vsynth2-dnxhd-720p-10bit
  • [DH] tests/ref/vsynth/vsynth2-prores
  • [DH] tests/ref/vsynth/vsynth2-prores_ks

• How to use find to match substring of files to be concatted ?

  23 mars 2023, par Russell Batt

  complete beginner here, so sorry if this is painfully obvious. I'm trying to write a shell script to ffmpeg concat protocol a bunch of split video files together by looping over the files and dynamically adding the correct parts to be joined together. For example, turning this :
  

  


  titlea-00001234-01.ts
  
titlea-00001234-02.ts
  
titlea-00001234-03.ts
  
titleb-00001234-01.ts
  
titleb-00004321-02.ts
  
titleb-00004321-03.ts
  

  


  into this :
  

  


  titlea-00001234.mp4
  
titleb-00004321.mp4
  

  


  by doing this

  


  ffmpeg -i "concat:titlea-00001234-01.ts|titlea-00001234-02.ts|titlea-00001234-03.ts" -c copy titlea-00001234.mp4
ffmpeg -i "concat:titleb-00001234-01.ts|titleb-00001234-03.ts|titleb-00001234-03.ts" -c copy titleb-00001234.mp4


  


  But what I'm having trouble with is using find to add the correct parts after "concat:".

  


  Here's my best attempt :

  


  #!/bin/bash
for i in /path/to/files/*.ts
    do
        if [[ "$i" =~ (-01) ]]
        then
            j="${i##*/}"
            k="${j%-0*}"
            ffmpeg -i `concat:( find /path/to/files/ -type f -name "{$k}*" -exec printf "%s\0" {} + )` -c copy /path/to/output/"{$k%.ts}.mp4"
        else
            echo "no files to process"
            exit 0
        fi
    done


  


  But this gives an error of "No such file or directory".

  
Edit This solution worked perfectly for my needs https://stackoverflow.com/a/75807616/21403800 Thanks @pjh and everyone else for taking the time to help