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• Extracting subclip from a .webm file with ffmpeg [migrated]

  19 juin 2013, par user815423426

  I am trying to extract a subclip from a webm file and write to an mp4 fil. I have the following command line :

  ffmpeg -ss 560 -i input.webm -ss 20 -t 46 -acodec copy -vcodec copy output.mp4

  but I get the following error :

  ffmpeg version 1.2 Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Mar 22 2013 10:42:11 with gcc 4.7.2 (GCC)
  
    configuration: --prefix=/path/to/installations --enable-shared --enable-gpl --en
  
  able-nonfree --enable-version3 --enable-libx264                           
  
    libavutil      52. 18.100 / 52. 18.100
  
    libavcodec     54. 92.100 / 54. 92.100
  
    libavformat    54. 63.104 / 54. 63.104
  
    libavdevice    54.  3.103 / 54.  3.103
  
    libavfilter     3. 42.103 /  3. 42.103
  
    libswscale      2.  2.100 /  2.  2.100
  
    libswresample   0. 17.102 /  0. 17.102
  
    libpostproc    52.  2.100 / 52.  2.100
  
  Input #0, matroska,webm, from '/path/to/input.webm':                                          
  
    Duration: 01:13:20.32, start: 0.000000, bitrate: 2006 kb/s
  
      Stream #0:0(eng): Video: vp8, yuv420p, 640x480, SAR 1:1 DAR 4:3, 30 fp,
  
   30 tbr, 1k tbn, 1k tbc (default)                                         
  
      Stream #0:1(eng): Audio: vorbis, 44100 Hz, stereo, fltp (default)
  
  [mp4 @ 0x1493c340] track 0: could not find tag, codec not currently support
  
  ed in container                                                           
  
  Output #0, mp4, to '/path/to/output.mp4':                         
  
    Metadata:
  
      encoder         : Lavf54.63.104
  
      Stream #0:0(eng): Video: vp8, yuv420p, 640x480 [SAR 1:1 DAR 4:3], q=2-3
  
  1, 30 fps, 90k tbn, 1k tbc (default)                                      
  
      Stream #0:1(eng): Audio: vorbis ([221][0][0][0] / 0x00DD), 44100 Hz, st
  
  ereo (default)                                                            
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #0:1 -> #0:1 (copy)
  
  Could not write header for output file #0 (incorrect codec parameters ?): O
  
  peration not permitted                                                    

  The strange thing is that the following works well for extracting files from mp4 to mp4

  ffmpeg -ss 560 -i input.mp4 -ss 20 -t 46 -acodec copy -vcodec copy output.mp4

• Making Sure The PNG Gets There

  14 juin 2013, par Multimedia Mike — General

  Rewind to 1999. I was developing an HTTP-based remote management interface for an embedded device. The device sat on an ethernet LAN and you could point a web browser at it. The pitch was to transmit an image of the device’s touch screen and the user could click on the picture to interact with the device. So we needed an image format. If you were computing at the time, you know that the web was insufferably limited back then. Our choice basically came down to GIF and JPEG. Being the office’s annoying free software zealot, I was championing a little known up and coming format named PNG.

  So the challenge was to create our own PNG encoder (incorporating a library like libpng wasn’t an option for this platform). I seem to remember being annoyed at having to implement an integrity check (CRC) for the PNG encoder. It’s part of the PNG spec, after all. It just seemed so redundant. At the time, I reasoned that there were 5 layers of integrity validation in play.

  I don’t know why, but I was reflecting on this episode recently and decided to revisit it. Here are all the encapsulation layers of a PNG file when flung over an ethernet network :

  
  
  

  So there are up to 5 encapsulations for the data in this situation. At the innermost level is the image data which is compressed with the zlib DEFLATE method. At first, I thought that this also had a CRC or checksum. However, in researching this post, I couldn’t find any evidence of such an integrity check. Further, I don’t think we bothered to compress the PNG data in this project long ago. It was a small image, monochrome, and transferring via LAN, so the encoder could get away with signaling uncompressed data.

  The graphical data gets wrapped up in a PNG chunk and all PNG chunks have a CRC. To transmit via the network, it goes into a TCP frame, which also has a checksum. That goes into an IP packet. I previously believed that this represented another integrity check. While an IP frame does have a checksum, the checksum only covers the IP header and not the payload. So that doesn’t really count towards this goal.

  Finally, the data gets encapsulated into an ethernet frame which has — you guessed it — a CRC.

  I see that other link layer protocols like PPP and wireless ethernet (802.11) also feature frame CRCs. So I guess what I’m saying is that, if you transfer a PNG file over the network, you can be confident that the data will be free of any errors.

• Concat two mp4 files with ffmpeg without losing quality [migrated]

  13 juin 2013, par jenia

  i have now a problem with concatenating of 2 videos using ffmpeg.
  So, i am encoding the source mp4 files to ts with

     ffmpeg -i output1.mp4 -scodec copy -vbsf h264_mp4toannexb i0.ts

  but the file i get looks much worse, then the source file.

  here is the information about both the files

     Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'output1.mp4':
  
     Metadata:
  
     major_brand     : isom
  
     minor_version   : 1
  
     compatible_brands: isom
  
     creation_time   : 2013-06-13 15:40:36
  
     Duration: 00:00:15.72, start: 0.000000, bitrate: 2053 kb/s
  
     Stream #0.0(und): Video: h264 (High), yuv420p, 1280x720, 1931 kb/s, 25 fps, 25 tbr,   12800 tbn, 50 tbc
  
     Stream #0.1(und): Audio: aac, 44100 Hz, stereo, s16, 128 kb/s
  
  
  
    Input #0, mpegts, from 'i0.ts':
  
    Duration: 00:00:15.64, start: 1.400000, bitrate: 1382 kb/s
  
    Program 1 
  
    Metadata:
  
    service_name    : Service01
  
    service_provider: Libav
  
    Stream #0.0[0x100]: Video: mpeg2video (Main), yuv420p, 1280x720 [PAR 1:1 DAR 16:9], 104857 kb/s, 25 fps, 25 tbr, 90k tbn, 50 tbc
  
    Stream #0.1[0x101](und): Audio: mp2, 44100 Hz, stereo, s16, 128 kb/s

  So, how can i solve this problem ?
  Thanks in advance !