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• 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.

• Creating HLS variants with FFMPEG

  4 janvier 2017, par user2491463

  I am starting with a high res video file and I would like to create 3 variants, low quality, mid quality, and high quality for mobile streaming. I want these mid/low/high variants to be segmented into ts pieces that the m3u8 file will be pointing that. Is there a way to do this in one line in ffmpeg ?

  I have successfully generated an m3u8 file and ts segments with ffmpeg, do I need to do this 3x and set specs for low/mid/high ? If so, how do I get the singular m3u8 file to point to all variants as opposed to one for each variant ?

  This is the command I used to generate the m3u8 file along with the ts segments.

  ffmpeg -i C:\Users\george\Desktop\video\hos.mp4 -strict -2 -acodec aac -vcodec libx264 -crf 25 C:\Users\user\Desktop\video\hos_Phone.m3u8

• FFmpeg error : Unable to find a suitable output format for ''

  11 juillet 2020, par Benjamin Basmaci

  I'm new to ffmpeg as well as Android programming. I'm trying to load a video from a URL and crop it with ffmpeg. I want to save that video to a file. This is the command I found online :

  


  "-i " + videoUrl + "-filter:v crop=240:120:100:100 -c:a copy test.mp4"


  


  I have tried it and got the error Unable to find a suitable output format for ''

  


  So I tried to narrow the possible cause down and tried these commands as well :

  


  "-i " + videoUrl + " -c:v copy -c:a copy test.mp4"
"-i " + videoUrl + " -c:v copy test.mp4"
"-i " + videoUrl + " -c:a copy test.mp4"
"-i " + videoUrl + " test.mp4"


  


  So with that last one I basically boiled it down to the bare minimum of what a comment needs, as far as I know. But still, same result.

  


  All of them give me the same error. Here is the full output I got via FFmpeg.getLatestOutput()

  


  ffmpeg version v4.2-dev-480 Copyright (c) 2000-2018 the FFmpeg developers
      built with Android (4751641 based on r328903) clang version 7.0.2 (https://android.googlesource.com/toolchain/clang 003100370607242ddd5815e4a043907ea9004281) (https://android.googlesource.com/toolchain/llvm 1d739ffb0366421d383e04ff80ec2ee591315116) (based on LLVM 7.0.2svn)
      configuration: --cross-prefix=i686-linux-android- 
                     --sysroot=/files/android-sdk/ndk-bundle/toolchains/mobile-ffmpeg-api-24-i686/sysroot
                     --prefix=/home/taner/Projects/mobile-ffmpeg/prebuilt/android-x86/ffmpeg 
                     --pkg-config=/usr/bin/pkg-config --enable-version3 --arch=i686 --cpu=i686 
                     --target-os=android --disable-neon --disable-asm --disable-inline-asm 
                     --enable-cross-compile --enable-pic --enable-jni --enable-lto 
                     --enable-optimizations --enable-swscale --enable-shared 
                     --disable-v4l2-m2m --disable-outdev=v4l2 
                     --disable-outdev=fbdev --disable-indev=v4l2 --disable-indev=fbdev 
                     --enable-small --disable-openssl --disable-xmm-clobber-test 
                     --disable-debug --disable-neon-clobber-test --disable-programs 
                     --disable-postproc --disable-doc --disable-htmlpages 
                     --disable-manpages --disable-podpages --disable-txtpages 
                     --disable-static --disable-sndio --disable-schannel 
                     --disable-securetransport --disable-xlib --disable-cuda 
                     --disable-cuvid --disable-nvenc --disable-vaapi --disable-vdpau 
                     --disable-videotoolbox --disable-audiotoolbox --disable-appkit 
                     --disable-alsa --disable-cuda --disable-cuvid --disable-nvenc 
                     --disable-vaapi --disable-vdpau --enable-libfontconfig 
                     --enable-libfreetype --enable-libfribidi --enable-gmp --enable-gnutls 
                     --enable-libmp3lame --enable-libass --enable-iconv --enable-libtheora 
                     --enable-libvorbis --enable-libvpx --enable-libwebp --enable-libxml2 
                     --enable-libopencore-amrnb --enable-libopencore-amrwb 
                     --enable-libshine --enable-libspeex --enable-libwavpack 
                     --enable-libkvazaar --enable-libilbc --enable-libopus 
                     --enable-libsnappy --enable-libsoxr --enable-libaom --enable-libtwolame 
                     --disable-sdl2 --enable-zlib --enable-mediacodec
      libavutil      56. 25.100 / 56. 25.100
      libavcodec     58. 42.104 / 58. 42.104
      libavformat    58. 25.100 / 58. 25.100
      libavdevice    58.  6.101 / 58.  6.101
      libavfilter     7. 46.101 /  7. 46.101
      libswscale      5.  4.100 /  5.  4.100
      libswresample   3.  4.100 /  3.  4.100
    Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'https://MyVideoUrl.com/example':
      Metadata:
        major_brand     : mp42
        minor_version   : 512
        compatible_brands: isomiso2avc1mp41
        creation_time   : 2019-01-28T13:44:03.000000Z
        encoder         : HandBrake 1.2.0 2018122200
      Duration: 00:00:14.33, start: 0.000000, bitrate: 4478 kb/s
        Stream #0:0(und): Video: h264 (avc1 / 0x31637661), yuv420p(tv, bt709), 1520x2700 [SAR 6075:4864 DAR 45:64], 4475 kb/s, 30.07 fps, 30 tbr, 90k tbn, 180k tbc (default)
        Metadata:
          creation_time   : 2019-01-28T13:44:03.000000Z
          handler_name    : VideoHandler
    [NULL @ 0x91833c00] Unable to find a suitable output format for ''
    : Invalid argument
    .


  


  Why does ffmpeg assume that I have given it no output format and what I need to do to make this work ?

  


  I'm using implementation 'com.arthenica:mobile-ffmpeg-full:4.2'.