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• avutil/file : allow mapping 0 byte files with av_file_map

  6 septembre 2018, par Marton Balint

  avutil/file : allow mapping 0 byte files with av_file_map
  Signed-off-by : Marton Balint <cus@passwd.hu>
  

  • [DH] libavutil/file.c
  • [DH] libavutil/file.h
  • [DH] libavutil/version.h

• MPEG DASH : Playing video segments from .m4s files instead of byte ranges in the MPD File using Simple DASH Player

  1er novembre 2018, par Trycoder

  I have followed the tutorial from the link below to create an MPEG DASH player using HTML5 and javascript.
  Building a simple MPEG dash player using HTML5 and JS.

  In the given tutorial, it is possible to play the video segments using byte ranges. But for my application, I need the following features.

  1. The video player should read the .m4s segment files and play the video instead of byte ranges.
  2. The amount of data in the MediaSource buffer should be calculated periodically, also the amount of space left in the buffer.

  Are these possible in the given player or Is there a better MPEG DASH Player with the above features ?

  PS : The MPD File is created using FFmpeg.

  ffmpeg  -f  avfoundation -video_size 1280x720 -framerate 30 -i 0 -vcodec libx264  -acodec aac  -b:v 800k  -f dash  -use_template 0  -min_seg_duration 4000 -single_file 1  -start_at_zero -live 1  ffmpeg.mpd

  Also, I tried using the DASH.js player but the documentation is very vast in it. Can we get the size of the source buffer in dash.js (The space available in the source buffer and also the amount of space filled) ? This is the main feature which is required for my project.

  Edit :
  Code which I tried

• Creating an Init file from existing non-fragmented, segmented MP4 files

  20 novembre 2018, par slhck

  I am performing chunked encodes of longer video files, where I’ve split the original file into individual sequences that I have encoded separately. These sequences are files of different length, depending on where the scene cuts appear—they may be between 2 and 5 seconds long. They all start with an I-frame and are standalone.

  My encoded sequences are all MP4s, e.g. :

  test_0000.mp4
  
  test_0001.mp4
  
  test_0002.mp4
  
  test_0003.mp4
  
  test_0004.mp4

  They all have common properties :

  $ mp4info test_0000.mp4
  
  
  
  File:
  
    major brand:      isom
  
    minor version:    200
  
    compatible brand: isom
  
    compatible brand: iso2
  
    compatible brand: mp41
  
    fast start:       no
  
  
  
  Movie:
  
    duration:   2016 ms
  
    time scale: 1000
  
    fragments:  no
  
  
  
  ...

  Now, in order to play those with a DASH player, I have to create an initialization segment and individual fragmented MP4s.

  I could generate the fragmented MP4s via mp4fragment which I run on each standalone MP4 file :

  $ mp4info test_0000.m4s
  
  File:
  
    major brand:      isom
  
    minor version:    200
  
    compatible brand: isom
  
    compatible brand: iso2
  
    compatible brand: mp41
  
    compatible brand: iso5
  
    fast start:       yes
  
  
  
  Movie:
  
    duration:   2016 ms
  
    time scale: 1000
  
    fragments:  yes
  
  
  
  ...

  But obviously, these are now not according to spec, and all contain a moov atom :

  

  What I’d need is individual media segments with only one moof and mdat box, which then require an initialization segment with only a moov box.

  How can I generate that from the existing, already encoded segments ?

  I know this appears like an XY problem. In principle, I could already segment my original file directly after encoding, and run those encodes at the same time, e.g. using ffmpeg’s dash muxer, or MP4Box, however :

  • There is almost no control over the resulting segment sizes, with respect to minimum and maximum duration
  • This approach does not parallelize

  I have also checked Bento4 ; it does not seem to offer this functionality. Neither does FFmpeg. MP4Box behaves similarly. They all assume you have one long file to start with.

  ---

  I see I could splice off the ftyp and moov boxes from these “fake fragments” in order to create an initialization segment. But I would end up with segments containing multiple moof and mdat boxes, which is not according to the specification – it only allows one fragment and media data box :

  4. Media Segments

  […] one optional Segment Type Box (styp) followed by a single Movie Fragment Box (moof) followed by one or more Media Data Boxes (mdat).

  I guess I can live with this the styp not being present.