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• 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.

• How to merge segmented webvtt subtitle files and output a single file ?

  15 février, par Dobbelina

  How to merge a segmented webvtt subtitle file and output a single file ?,
m3u8 looks like this example :

  



  #EXTM3U
#EXT-X-VERSION:4
#EXT-X-PLAYLIST-TYPE:VOD
#EXT-X-MEDIA-SEQUENCE:1
#EXT-X-INDEPENDENT-SEGMENTS
#EXT-X-TARGETDURATION:4
#USP-X-TIMESTAMP-MAP:MPEGTS=900000,LOCAL=1970-01-01T00:00:00Z
#EXTINF:4, no desc
0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-1.webvtt
#EXTINF:4, no desc
0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-2.webvtt
#EXTINF:4, no desc
0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-3.webvtt
#EXTINF:4, no desc
0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-4.webvtt
#EXTINF:4, no desc
0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-5.webvtt
#EXTINF:4, no desc
0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-6.webvtt
#EXT-X-ENDLIST


  



  I noticed that each segment is not synchronized/cued against total playing time, but against the individual ts segments.
If ffmpeg could be used to do this, what magic input do i need to give it ?

  



  A single correctly cued vtt or srt file is what i want.

  



  I have a great appetite and don't like chunks, lol !

  



  Thanks for any replies you lovely people !

  



  ---

  



  With this i get a merged vtt file, but the cues are all wrong :

  



  ffmpeg -i "https://cmoreseusphlsvod60.akamaized.net/vod/bea44/0ghzi1b2cz5(11792107_ISMUSP).ism/0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000.m3u8" -f segment -segment_time 4 -segment_format webvtt -scodec copy out-%05d.vtt


  



  Each segment is not synchronized/cued against total playing time, but against the individual ts segments.
Example output of above command :

  



  WEBVTT

00:00.000 --> 00:03.040
Du har aktier i ett företag
som saknar framtid.

00:00.000 --> 00:03.280
De vill ha aktierna.
Du känner dem inte, Olga.

00:00.000 --> 00:01.720
De som får Kastrups aktier vinner.


  



  Cues all start like this which isn't very helpfull : 00:00.000

  



  Some segments contains no cues, like segment 15 for example :
https://cmoreseusphlsvod60.akamaized.net/vod/bea44/0ghzi1b2cz5(11792107_ISMUSP).ism/0ghzi1b2cz5(11792107_ISMUSP)-textstream_swe=2000-15.webvtt

  



  


  "A WebVTT Segment MAY contain no cues ; this indicates that no
 subtitles are to be displayed during that period."

  


  


• How to detect blue screen of ffmpeg video packet ?

  28 novembre 2017, par 심상원

  Good morning. There is one question about FFMPEG.

  I’m using FFMPEG to study C ++ on Linux.

  When the camera spirituality is RTSP and the format is H.264,

  I would like to determine if the camera image is a blue screen, but the following concepts are confusing.

  1. KeyFrame comes in 1 second or every X seconds cycle. Does the KeyFrame get delivered from the camera even if it is still the same image ?

  2. If the KeyFrame is delivered, is the size of the packet transmitted between the cycles zero ?

  3. If the above method is the same as normal image, should I compare the individual frames after decoding ?

  If you do not have any of these questions, please let me know if you have a good way.

  Thank you.