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• ffprobe stream selection for encoding

  22 octobre 2014, par user3652819

  when I run ffmpeg, I can see "default" audio and video stream :

  Stream #0:0(und): Video: h264 (Constrained Baseline) (avc1 / 0x31637661), yuv420p, 960x400 [SAR 1:1 DAR 12:5], 3859 kb/s, 23.98 fps, 23.98 tbr, 24k tbn, 47.95 tbc 
  
    (default)
  
  Metadata:
  
    creation_time   : 2013-05-03 22:50:47
  
    handler_name    : GPAC ISO Video Handler
  
  Stream #0:1(und): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 92 kb/s 
  
    (default)
  
   Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : SoundHandler
  
  Stream #0:2: Video: mjpeg, yuvj420p(pc), 675x1000 [SAR 72:72 DAR 27:40], 90k tbr, 90k tbn, 90k tbc

  As I understand, this stream selected by ffmpeg as input when encoding, if map option not set.

  How can I get "default" stream using ffprobe ?

  Sorry for English

• WebRTC books – a brief review

  1er janvier 2014, par silvia

  I just finished reading Rob Manson’s awesome book “Getting Started with WebRTC” and I can highly recommend it for any Web developer who is interested in WebRTC.

  Rob explains very clearly how to create your first video, audio or data peer-connection using WebRTC in current Google Chrome or Firefox (I think it also now applies to Opera, though that wasn’t the case when his book was published). He makes available example code, so you can replicate it in your own Web application easily, including the setup of a signalling server. He also points out that you need a ICE (STUN/TURN) server to punch through firewalls and gives recommendations for what software is available, but stops short of explaining how to set them up.

  Rob’s focus is very much on the features required in a typical Web application :

  • video calls
  • audio calls
  • text chats
  • file sharing

  In fact, he provides the most in-depth demo of how to set up a good file sharing interface I have come across.

  Rob then also extends his introduction to WebRTC to two key application areas : education and team communication. His recommendations are spot on and required reading for anyone developing applications in these spaces.

  —

  Before Rob’s book, I have also read Alan Johnson and Dan Burnett’s “WebRTC” book on APIs and RTCWEB protocols of the HTML5 Real-Time Web.

  Alan and Dan’s book was written more than a year ago and explains that state of standardisation at that time. It’s probably a little out-dated now, but it still gives you good foundations on why some decisions were made the way they are and what are contentious issues (some of which still remain). If you really want to understand what happens behind the scenes when you call certain functions in the WebRTC APIs of browsers, then this is for you.

  Alan and Dan’s book explains in more details than Rob’s book how IP addresses of communication partners are found, how firewall holepunching works, how sessions get negotiated, and how the standards process works. It’s probably less useful to a Web developer who just wants to implement video call functionality into their Web application, though if something goes wrong you may find yourself digging into the details of SDP, SRTP, DTLS, and other cryptic abbreviations of protocols that all need to work together to get a WebRTC call working.

  —

  Overall, both books are worthwhile and cover different aspects of WebRTC that you will stumble across if you are directly dealing with WebRTC code.

• Cannot concatenate videos ffmpeg [on hold]

  1er mai 2014, par Paul Prescod

  I have a bitmap that I would like to concatenate to the front of many videos as a sort of title screen or disclaimer screen.

  I try to turn it into a video with the same attributes as the rest of the video. So first I introspect the video :

  ffmpeg version 2.2.1 Copyright (c) 2000-2014 the FFmpeg developers
  
    built on Apr 11 2014 22:50:38 with Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/2.2.1 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-nonfree --enable-hardcoded-tables --enable-avresample --enable-vda --cc=clang --host-cflags= --host-ldflags= --enable-libx264 --enable-libfaac --enable-libmp3lame --enable-libxvid
  
    libavutil      52. 66.100 / 52. 66.100
  
    libavcodec     55. 52.102 / 55. 52.102
  
    libavformat    55. 33.100 / 55. 33.100
  
    libavdevice    55. 10.100 / 55. 10.100
  
    libavfilter     4.  2.100 /  4.  2.100
  
    libavresample   1.  2.  0 /  1.  2.  0
  
    libswscale      2.  5.102 /  2.  5.102
  
    libswresample   0. 18.100 /  0. 18.100
  
    libpostproc    52.  3.100 / 52.  3.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'EO1.mp4':
  
    Metadata:
  
  major_brand     : isom
  
  minor_version   : 512
  
  compatible_brands: isomiso2avc1mp41
  
  creation_time   : 1970-01-01 00:00:00
  
  encoder         : Lavf52.78.3
  
    Duration: 00:00:17.77, start: 0.000000, bitrate: 582 kb/s
  
  Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 584x328 [SAR 1:1 DAR 73:41], 512 kb/s, 23.98 fps, 23.98 tbr, 1199 tbn, 47.96 tbc (default)
  
  Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : VideoHandler
  
  Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 64 kb/s (default)
  
  Metadata:
  
    creation_time   : 1970-01-01 00:00:00
  
    handler_name    : SoundHandler

  Then I try and create a similar file :

  /usr/local/Cellar/ffmpeg/2.2.1/bin/ffmpeg -y -loop 1 -i Disclaimer.png -c:v libx264 -r 23.98 -t 5 -pix_fmt yuv420p -profile:v main disclaimer.mp4

  It seems to work okay. The video plays I would expect it to. The attributes turn out very similar. Here is a diff :

  < Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'disclaimer.mp4':
  
  ---
  
  > Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'EO1.mp4':
  
  18,20c18,21
  
  <     encoder         : Lavf55.33.100
  
  <   Duration: 00:00:05.01, start: 0.000000, bitrate: 21 kb/s
  
  <     Stream #0:0(und): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 584x328 [SAR 1:1 DAR 73:41], 17 kb/s, 23.98 fps, 23.98 tbr, 19184 tbn, 47.96 tbc (default)
  
  ---
  
  >     creation_time   : 1970-01-01 00:00:00
  
  >     encoder         : Lavf52.78.3
  
  >   Duration: 00:00:17.77, start: 0.000000, bitrate: 582 kb/s
  
  >     Stream #0:0(eng): Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 584x328 [SAR 1:1 DAR 73:41], 512 kb/s, 23.98 fps, 23.98 tbr, 1199 tbn, 47.96 tbc (default)
  
  21a23
  
  22a25,28
  
  >     Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 64 kb/s (default)
  
  >     Metadata:
  
  >       handler_name    : SoundHandler

  But when I try to concatenate, I get errors.

  > $ cat temporary.txt 
  
  
  
      file disclaimer.mp4
  
      file EO1.mp4

  /usr/local/Cellar/ffmpeg/2.2.1/bin/ffmpeg -y -f concat -i temporary.txt -c copy output.mp4

  [concat @ 0x7fd880806600] Estimating duration from bitrate, this may be inaccurate
  
  Input #0, concat, from 'temporary.txt':
  
    Duration: 00:00:00.02, start: 0.000000, bitrate: 17 kb/s
  
  Stream #0:0: Video: h264 (Main) (avc1 / 0x31637661), yuv420p, 584x328 [SAR 1:1 DAR 73:41], 17 kb/s, 23.98 fps, 23.98 tbr, 19184 tbn, 47.96 tbc
  
  Output #0, mp4, to 'output.mp4':
  
    Metadata:
  
  encoder         : Lavf55.33.100
  
  Stream #0:0: Video: h264 ([33][0][0][0] / 0x0021), yuv420p, 584x328 [SAR 1:1 DAR 73:41], q=2-31, 17 kb/s, 23.98 fps, 19184 tbn, 19184 tbc
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
  Press [q] to stop, [?] for help
  
  [mp4 @ 0x7fd880829a00] Non-monotonous DTS in output stream 0:0; previous: 93600, current: 5951; changing to 93601. This may result in incorrect timestamps in the output file.
  
  [concat @ 0x7fd880806600] Invalid stream index 1
  
  [mp4 @ 0x7fd880829a00] Non-monotonous DTS in output stream 0:0; previous: 93601, current: 6001; changing to 93602. This may result in incorrect timestamps in the output file.
  
  [concat @ 0x7fd880806600] Invalid stream index 1
  
  [mp4 @ 0x7fd880829a00] Non-monotonous DTS in output stream 0:0; previous: 93602, current: 6051; changing to 93603. This may result in incorrect timestamps in the output file.

  ...

  frame=  546 fps=0.0 q=-1.0 Lsize=    1127kB time=00:00:04.90 bitrate=1882.9kbits/s    
  
  video:1123kB audio:0kB subtitle:0 data:0 global headers:0kB muxing overhead 0.349865%

  The output looks like it only has my disclaimer file in it, not the rest of the video.

  I’m also confused why it feels like it needs to "estimate" anything. It knows the input FPS and input durations. I’m not sure if this is the problem or not. Maybe its just a bug.