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• How to send an mpeg_ts stream verbatim over rtp

  30 mars 2018, par Bruce Adams

  I’m trying to write some software to capture and process data from an mpeg_ts stream.
  As part of this I need, for testing, to generate a test mpeg_ts streams for my software to capture

  One option for this is to save a real stream to disk.
  So with that in mind I have a source transport stream which is being unicast via rtp to my box via port 1234. I can view it in vlc using :

  vlc rtp://@:1234

  and I can move between channels via the "programme" menu.
  subtitles are available but no EPG
  kaffeine works as well but only shows the first channel

  I can save this stream using :

  ffmpeg -i rtp://172.16.13.81:1235 -map 0 -copy_unknown -c copy save_ffmpeg.ts

  note : that rtp ://@:1235 does not work you need your full IP address though udp ://@:1235 does work for udp streams - see https://ffmpeg.zeranoe.com/forum/viewtopic.php?t=2386

  However there is a problem. When I try to open the resulting file save_ffmpeg.ts in VLC
  instead of opening one channel at a time it opens a new window for each channel which indicates an issue.

  If on the other hand I save it using :

  cvlc rtp://@:1235 :demux=dump :demuxdump-file=save_vlc.ts

  the resulting ts file can be viewed as normal.
  What is the difference ?

  Looking at the output of mediainfo on save_ffmpeg.ts vs save_vlc.ts
  I can see that ffmpeg has stripped the streams labelled Menu #1 to Menu #5.

  >mediainfo save_ffmpeg.ts  | grep -E '^[A-Za-z]+ #'
  
  Video #1
  
  Video #2
  
  Video #3
  
  Video #4
  
  Video #5
  
  Audio #1
  
  Audio #2
  
  Audio #3
  
  Audio #4
  
  Audio #5
  
  Audio #6
  
  Audio #7
  
  >mediainfo save_vlc.ts  | grep -E '^[A-Za-z]+ #'
  
  Video #1
  
  Video #2
  
  Video #3
  
  Video #4
  
  Video #5
  
  Audio #1
  
  Audio #2
  
  Audio #3
  
  Audio #4
  
  Audio #5
  
  Audio #6
  
  Audio #7
  
  Menu #1
  
  Menu #2
  
  Menu #3
  
  Menu #4
  
  Menu #5

  I tried adding -map_metadata 0 but to no avail.

  Q1 What is wrong with the ffmpeg command ?
  How do I get it to also save the menu streams ?

  Now I can send the ts that has the menu with ffmpeg using :

  ffmpeg -re -i save_vlc.ts -c copy -f mpegts udp://127.0.0.1:9999

  to get one channel
  but again if I try to send everything :

  ffmpeg -re -i ./save_file.ts -map 0 -map_metadata 0 -copy_unknown -c copy -f rtp_mpegts rtp://127.0.0.1:9999

  then :

  vlc rtp://127.0.0.1:9999

  opens a window for each and every channel.

  Q2 How do I fix this ?

  Q3 What would the equivalent gstreamer commands be to send and recieve ts files ?

  The relevance of the final question is that one of the options being considered for implementing the MPEG_TS reader is gstreamer. Though, it probably warrants a question of its own.

• movtextenc : fix handling of utf-8 subtitles

  28 mars 2018, par Philip Langdale

  movtextenc : fix handling of utf-8 subtitles
  See the earlier fix for movtextdec for details. The equivalent bug is
  
  present on the encoder side as well.
  We need to track the text length in 'characters' (which seems to really
  
  mean codepoints) to ensure that styles are applied across the correct
  
  ranges.
  

  • [DH] libavcodec/movtextenc.c

• FFmpeg - Delay Only Video Stream Of Audio Linked dshow Input

  15 avril 2018, par Nimble

  I’m having a slight issue trying to sync my audio and video up with an acceptable margin of error. Here is my command :

  ffmpeg -y -thread_queue_size 9999 -indexmem 9999 -guess_layout_max 0 -f dshow -video_size 3440x1440 -rtbufsize 2147.48M ^
  
  -framerate 100 -pixel_format nv12 -i video="Video (00 Pro Capture HDMI 4K+)":audio="SPDIF/ADAT (1+2) (RME Fireface UC)" ^
  
  -map 0:0,0:1 -map 0:1 -flags +cgop -force_key_frames expr:gte(t,n_forced*2) -c:v h264_nvenc -preset: llhp -pix_fmt nv12 ^
  
  -b:v 250M -minrate 250M -maxrate 250M -bufsize 250M -c:a aac -ar 44100 -b:a 384k -ac 2 -r 100 -af "aresample=async=250" ^
  
  -vsync 1 -max_muxing_queue_size 9999 -f segment -segment_time 600 -segment_wrap 9 -reset_timestamps 1 ^
  
  C:\Users\djcim\Videos\PC\PC\PC%02d.ts

  My problem is the video comes in slightly ahead of the audio, I can use -itsoffset but then I have to call the video and audio as separate inputs as -itsoffset offsets both audio and video. While this may seem the obvious solution it causes inconsistent audio synchronization if the audio isn’t called with the video. Basically if both audio and video aren’t called at the same time the video can now be ahead or behind with a 2-3 frame margin. When I call them at the same time the video consistently comes in 2 frames ahead of the audio, every time. I just need a way to delay only the video stream without delaying the audio while keeping both audio and video linked from the beginning. I’ve tried this with no luck :

  ffmpeg -y -thread_queue_size 9999 -indexmem 9999 -guess_layout_max 0 -f dshow -video_size 3440x1440 -rtbufsize 2147.48M ^
  
  -framerate 200 -pixel_format nv12 -i video="Video (00 Pro Capture HDMI 4K+)":audio="SPDIF/ADAT (1+2) (RME Fireface UC)" ^
  
  -flags +cgop -force_key_frames expr:gte(t,n_forced*2) -c:v h264_nvenc -preset: llhp -pix_fmt nv12 -b:v 250M ^
  
  -minrate 250M -maxrate 250M -bufsize 250M -c:a aac -ar 44100 -b:a 384k -ac 2 -r 100 ^
  
  -filter_complex "[0:v] setpts=PTS-STARTPTS+.032/TB [v]; [0:a] asetpts=PTS-STARTPTS, aresample=async=250 [a]" -map [v] ^
  
  -map [a] -vsync 1 -max_muxing_queue_size 9999 -f segment -segment_time 600 -segment_wrap 9 -reset_timestamps 1 ^
  
  C:\Users\djcim\Videos\PC\PC\PC%02d.ts

  Just like -itsoffset both video and audio are being delayed. You can delay solely audio with adelay, but there doesn’t seem to be a video delaying equivalent.

  Any help or advice would be greatly appreciated.