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• FFmpeg concat command changes start_time (ts chunks concatenation)

  29 septembre 2017, par Ales

  I concatenate ts chunks using ffmpeg command :
  ffmpeg -i "concat:input1.ts|input2.ts" -c copy output.ts

  For example video consists of 10 ts chunks, and we concatenate only two last chunks (ninth and tenth ts chunks). And we stream video consisting of old (1-8) ts chunks and new joint ts chunk. There is a problem with playback of result joint chunk. After investigation we found that in joint ts chunk some properties are differ :

  start_pts=127141
  
  start_time=1.412678

  Although in original (ninth) ts chunk they are :

  start_pts=2021483
  
  start_time=21.213400

  Start time and start_pts were changed, we suppose that playback issue is related to this properties in ts chunk.

  Is there a way to leave the old values (start_pts and start_time) for result joint ts chunk ?

• Using FFmpeg in .net ?

  17 juin, par daniel

  So I know its a fairly big challenge but I want to write a basic movie player/converter in c# using the FFmpeg library. However, the first obstacle I need to overcome is wrapping the FFmpeg library in c#. I've downloaded ffmpeg but couldn't compile it on Windows, so I downloaded a precompiled version for me. Ok awesome. Then I started looking for C# wrappers.

  



  I have looked around and have found a few wrappers such as SharpFFmpeg (http://sourceforge.net/projects/sharpffmpeg/) and ffmpeg-sharp (http://code.google.com/p/ffmpeg-sharp/). First of all, I wanted to use ffmpeg-sharp as its LGPL and SharpFFmpeg is GPL. However, it had quite a few compile errors. Turns out it was written for the mono compiler, I tried compiling it with mono but couldn't figure out how. I then started to manually fix the compiler errors myself, but came across a few scary ones and thought I'd better leave those alone. So I gave up on ffmpeg-sharp.

  



  Then I looked at SharpFFmpeg and it looks like what I want, all the functions P/Invoked for me. However its GPL ? Both the AVCodec.cs and AVFormat.cs files look like ports of avcodec.c and avformat.c which I reckon I could port myself ? Then not have to worry about licencing.

  



  But I want to get this right before I go ahead and start coding. Should I :

  



  

  1. Write my own C++ library for interacting with ffmpeg, then have my C# program talk to the C++ library in order to play/convert videos etc.

  


  



  OR

  



  

  2. Port avcodec.h and avformat.h (is that all i need ?) to c# by using a whole lot of DllImports and write it entirely in C# ?

  


  



  First of all consider that I'm not great at C++ as I rarely use it but I know enough to get around. The reason I'm thinking #1 might be the better option is that most FFmpeg tutorials are in C++ and I'd also have more control over memory management than if I was to do it in c#.

  



  What do you think ?
Also would you happen to have any useful links (perhaps a tutorial) for using FFmpeg ?

  


• How to change metadata with ffmpeg/avconv without creating a new file ?

  16 mars, par Stephan Kulla

  I am writing a python script for producing audio and video podcasts. There are a bunch of recorded media files (audio and video) and text files containing the meta information.

  



  Now I want to program a function which shall add the information from the meta data text files to all media files (the original and the converted ones). Because I have to handle many different file formats (wav, flac, mp3, mp4, ogg, ogv...) it would be great to have a tool which add meta data to arbitrary formats.

  



  My Question :

  



  How can I change the metadata of a file with ffmpeg/avconv without changing the audio or video of it and without creating a new file ? Is there another commandline/python tool which would do the job for me ?

  



  What I tried so far :

  



  I thought ffmpeg/avconv could be such a tool, because it can handle nearly all media formats. I hoped, that if I set -i input_file and the output_file to the same file, ffmpeg/avconv will be smart enough to leave the file unchanged. Then I could set -metadata key=value and just the metadata will be changed.

  



  But I noticed, that if I type avconv -i test.mp3 -metadata title='Test title' test.mp3 the audio test.mp3 will be reconverted in another bitrate.

  



  So I thought to use -c copy to copy all video and audio information. Unfortunately also this does not work :

  



  :~$ du -h test.wav # test.wav is 303 MB big
303M    test.wav

:~$ avconv -i test.wav -c copy -metadata title='Test title' test.wav
avconv version 0.8.3-4:0.8.3-0ubuntu0.12.04.1, Copyright (c) 2000-2012 the
Libav    developers
built on Jun 12 2012 16:37:58 with gcc 4.6.3
[wav @ 0x846b260] max_analyze_duration reached
Input #0, wav, from 'test.wav':
Duration: 00:29:58.74, bitrate: 1411 kb/s
    Stream #0.0: Audio: pcm_s16le, 44100 Hz, 2 channels, s16, 1411 kb/s
File 'test.wav' already exists. Overwrite ? [y/N] y
Output #0, wav, to 'test.wav':
Metadata:
    title           : Test title
    encoder         : Lavf53.21.0
    Stream #0.0: Audio: pcm_s16le, 44100 Hz, 2 channels, 1411 kb/s
Stream mapping:
Stream #0:0 -> #0:0 (copy)
Press ctrl-c to stop encoding
size=     896kB time=5.20 bitrate=1411.3kbits/s    
video:0kB audio:896kB global headers:0kB muxing overhead 0.005014%

:~$ du -h test.wav # file size of test.wav changed dramatically
900K    test.wav


  



  You see, that I cannot use -c copy if input_file and output_file are the same. Of course I could produce a temporarily file :

  



  :-$ avconv -i test.wav -c copy -metadata title='Test title' test_temp.mp3
:-$ mv test_tmp.mp3 test.mp3


  



  But this solution would create (temporarily) a new file on the filesystem and is therefore not preferable.