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• avformat/segment : calculate segment durations correctly.

  7 janvier 2023, par Gyan Doshi

  avformat/segment : calculate segment durations correctly.
  segment_time and segment_times are defined as duration specifications, not
  
  timestamps, so calculation of segment duration must account for initial
  
  timestamp. Fixed.
  FATE ref for segment-mp4-to-ts changed on account of avoiding premature
  
  segment cut at the end of the first segment.
  

  • [DH] libavformat/segment.c
  • [DH] tests/ref/fate/segment-mp4-to-ts

• Calculate Bitrate from m3u8 ts files ffmpeg

  16 janvier 2017, par John

  I im using ffmpeg to connect to source and then make hls chunks (ts files) so that i can restream.

  I use following ffmpeg command to connect to source and generate hls segments :

  ffmpeg -y -nostdin -hide_banner -fflags +genpts -async 1 -i http://livestream.com/stream_name.ts -acodec copy -vcodec copy -scodec copy -f hls -hls_time 10 -hls_list_size 6 -hls_flags delete_segments /tmp/chunks/1_.m3u8

  Files are generated in /tmp/chunks/ folder ==>♦ 1_.m3u8 index file and 1_0.ts 1_1.ts 1_2.ts 1_3.ts

  So question is how can i calulate bitrate of stream ?

  If i use -f mpegts i can see from ffmpeg bitrate in terminal...but i don’t have chunks and opening stream is slow because stream is written in one file 1_.m3u8 on HDD and is growing..so this solution is not good.

  I use to calulate this way :

  When 1_1.ts is generated i read file size of 1_0.ts, read duration of 1_0.ts and calulate bitrate....let’s say that file size is : 2360904 bytes and file duration is : 12seconds) :

  I calucalte it using forumula :

  BITRATE = ((file_size / 1024) / file_duration) * 8 [kbit/s]

  So in my example this is :

  BITRATE = ((2360904 / 1024) / 12) * 8 = 1537 [kbit/s]

  Is this correct calulation and is this valid for ffmpeg ? Because in ffmpeg when i don’t use hls segmenter only -f mpegts i get bitrate around 1770kbit/s so would need to ask if this is correct way of calculating bitrate of stream or if is not how is correct way and formula...thanks.

  Also i need to use HLS segmenter from ffmpeg because this way streams opens very quick and cpu usage is lower (ram usage is 1-2MB per connection witch is good)

• How to calculate the start time of mp4 video ?

  27 mai 2022, par Neil Galiaskarov

  I am studying mp4 video structure. I have an issue with reading the start time value for the following mp4 video

  


  I have read this answer
mp4 video starts at different time on Quicktime/AVplayer vs Chrome/Firefox

  


  and it says that Edit atom can modify the start time.

  


  Using ffprobe I have the following output :

  


      "start_time": "0.033333",
    "duration_ts": 327,
    "duration": "10.900000",
    "bit_rate": "9420949",


  


  Using mp4dumper I have the following atoms structure which proves missing Edit atom file :

  


  ftyp (24 @ 0)
free (8 @ 24)
moov (7034 @ 32)
  mvhd (108 @ 40)
  trak (2883 @ 148)
      tkhd (92 @ 156)
      mdia (2783 @ 248)
          mdhd (32 @ 256)
          hdlr (52 @ 288)
          minf (2691 @ 340)
              smhd (16 @ 348)
              dinf (36 @ 364)
                  dref (28 @ 372)
                      url  (12 @ 388)
              stbl (2631 @ 400)
                  stsd (91 @ 408)
                      mp4a (75 @ 424)
                  stts (24 @ 499)
                  stsc (304 @ 523)
                  stsz (2056 @ 827)
                  stco (148 @ 2883)
  trak (4035 @ 3031)
      tkhd (92 @ 3039)
      mdia (3935 @ 3131)
          mdhd (32 @ 3139)
          hdlr (52 @ 3171)
          minf (3843 @ 3223)
              vmhd (20 @ 3231)
              dinf (36 @ 3251)
                  dref (28 @ 3259)
                      url  (12 @ 3275)
              stbl (3779 @ 3287)
                  stsd (163 @ 3295)
                      avc1 (147 @ 3311)
                  stts (24 @ 3458)
                  ctts (1960 @ 3482)
                  stsc (40 @ 5442)
                  stsz (1328 @ 5482)
                  stco (148 @ 6810)
                  stss (108 @ 6958)
mdat (13096745 @ 7066)


  


  How ffprobe calculates 0.033333 start time value ?