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• FFmpeg/C/C++ : where is located and how decode Closed Caption(608) in Matrox DVCPRO SD files using ffmpeg and c/c++ ?

  2 mars 2020, par Helmuth Schmitz

  I’m a lit bit crazy with some especific video files. I want to decode them using ffmpeg/c++, specifically decode 608 Closed Captions. The AVI file format/codec is DVCPRO at SD(720x480) resolution. The enconder is "Matrox DSX AVI file . Format : 6. Build : 1.0.0.451" That’s was ok, until moment i tried to see or decode 608 closed captions. There was nothing at line 21. So, i decid to play this file in Matrox Sample Video Player(an example of their SDK) and for my surprise there was 608 closed captions. So, i read Matrox SDK documentation, and found this

  Using closed caption information
  
  Some of the Matrox NTSC codecs can extract the closed caption information from the
  
  video buffers and store it as metadata in the compressed buffer. On decompression,
  
  these same codecs can restore the lines to their proper position. Other NTSC codecs
  
  just encode the closed caption lines as video data. The closed caption lines that are
  
  extracted are defined by the EIA-608 specification. The two lines are defined as lines
  
  21 from both the first and second fields.
  
  The following codecs keep the closed caption lines as metadata (NTSC only):
  
  • Matrox DV (encode and decode).
  
  • Matrox MPEG-2 I-frame (encode and decode).
  
  • Matrox MPEG-2 IBP, except 720×512 resolution (decode only).
  
  The following codecs keep the closed caption lines as video data (NTSC only):
  
  • Matrox D10 (encode and decode).
  
  • Matrox MPEG-2 IBP in 720 ×512 resolution (decode only).
  
  • Matrox M-JPEG (decode only).

  So, i thought that VBI or Closed Caption(608) will be stored at some metadata. But, exploring the entire file using ffmpeg/libavcodec with C/C++, i found nothing "hide" in metadata. Even in frames metadata. Is like magic. There is nothing in line 21 and nothing in metadata’s. So, how Matrox sample example is the only one video player that show’s it ?

• Can javascript MSE play segmented mp4 from the middle ?

  10 juillet 2020, par Elias Wagnerberger

  in my current project i have a video stream that ffmpeg encodes to a segmented mp4. that encoded data is piped into an application that sends that data to whomever connects to that application through a websocket. when a client connects i make sure to send the ftyp and the moov boxes first and then send the most recent segments recieved from ffmpeg.

  


  on the client side i just pass all binary data from the websocket to MSE.

  


  The problem i am facing is that this works if the client is connected from the very start and gets all the fragments that ffmpeg pipes out, but it does not work if the client connects in after ffmpeg sends its first few fragments.

  


  My question is :
Is it possible for MSE to play a fragmented mp4 from the middle when it is also provided the init segments ?

  


  If it is possible then how would that need to be implemented ?

  


  if it isnt possible then what format would allow me to stream live video over a websocket ?

  


• A Soundboard for Discord with Discord.py with already downloaded .mp3 files

  8 août 2019, par Kerberos Kev

  I’m setting up a discord bot with discord.py, and want to implement an soundboard.The soundboard should take already downloaded .mp3 files and play them in the discord. The bot already automatically joins and disconnects from a voice channel but does not play any of my sound files.

  I tried converting the mp3 file into an opus one and just play it without ffmpeg but this didn’t work either.

  import discord
  
  from discord.ext import commands
  
  from discord.utils import get
  
  from mutagen.mp3 import MP3
  
  import time
  
  import os
  
  
  
  client = commands.Bot(command_prefix='<')
  
  a = './'+'kurz-kacken.mp3'
  
  
  
  
  
  class Soundboard(commands.Cog):
  
  
  
      def __init__(self, client):
  
          self.client = self
  
  
  
      @commands.command(pass_context=True)
  
      async def soundboard(self, ctx, songname: str):
  
          channel = ctx.message.author.voice.channel
  
          voice = get(client.voice_clients, guild=ctx.guild)
  
  
  
          if voice and voice.is_connected():
  
              await voice.move_to(channel)
  
          else:
  
              voice = await channel.connect()
  
  
  
              print(f"The bot has connected to {channel}\n")
  
  
  
          # audio = MP3('./'+'kurz-kacken.mp3')
  
          # a = audio.info.length
  
          voice.play(discord.FFmpegPCMAudio('./'+'kurz-kacken.mp3'),
  
                     after=lambda e: print("Song done!"))
  
          voice.source = discord.PCMVolumeTransformer(voice.source)
  
          voice.source.volume = 0.07
  
          # time.sleep(a)
  
          await ctx.send(f'ended')
  
  
  
          if voice and voice.is_connected():
  
              await voice.disconnect()
  
  
  
  
  
  def setup(client):
  
      client.add_cog(Soundboard(client))