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• What Every Programmer Should Know

  24 décembre 2012, par Multimedia Mike — General

  During my recent effort to force myself to understand Unicode and modern text encoding/processing, I was reminded that this is something that “every programmer should just know”, an idea that comes up every so often, usually in relation to a subject in which the speaker is already an expert. One of the most absurd examples I ever witnessed was a blog post along the lines of “What every working programmer ought to know about [some very specific niche of enterprise-level Java programming]“. I remember reading through the article and recognizing that I had almost no knowledge of the material. Disturbing, since I am demonstrably a “working programmer”.

  For fun, I queried the googles on the matter of what ever programmer ought to know.

  Specific Topics
  Here is what every programmer should know about : Unicode, time, memory (simple), memory (extremely in-depth), regular expressions, search engine optimization, floating point, security, basic number theory, race conditions, managed C++, VIM commands, distributed systems, object-oriented design, latency numbers, rate monotonic algorithm, merging branches in Mercurial, classes of algorithms, and human names.

  Broader Topics
  20 subjects every programmer should know, 97 things every programmer should know, 12 things every programmer should know, things every programmer should know (27 items), 10 papers every programmer should read at least twice, 10 things every programmer should know for their first job.

  Meanwhile, I remain fond of this xkcd comic whose mouseover text describes all that a person genuinely needs to know. Still, the new year is upon us, a time when people often make commitments to bettering themselves, and it couldn’t hurt (much) to at least skim some of the lists and find out what you never knew that you never knew.

  What About Multimedia ?
  Reading the foregoing (or the titles of the foregoing pieces), I naturally wonder if I should write something about what every programmer should know about multimedia. I think it would look something like a multimedia programming FAQ. These are some items that I can think of :

  1. YUV : The other colorspace (since most programmers are only familiar with RGB and have no idea what to make of the YUV that comes out of most video decoding APIs)
  2. Why you can’t easily seek randomly to any specific frame in a video file (keyframe/interframe discussion and their implications)
  3. Understand your platform before endeavoring to implement multimedia software (modern platforms, particularly mobile platforms, probably provide everything you need in the native APIs and there is likely little reason to compile libavcodec for the platform)
  4. Difference between containers and codecs (longstanding item, but I would argue it’s less relevant these days due to standardization on the MPEG — MP4/H.264/AAC — stack)
  5. What counts as a multimedia standard in this day and age (comparing the foregoing MPEG stack with the WebM/VP8/Vorbis stack)
  6. Trade-offs to consider when engineering a multimedia solution
  7. Optimization doesn’t always work the way you think it does (not everything touted as a massive speed-up in the world of computing — whether it be multithreaded CPUs, GPGPUs, new SIMD instruction sets — will necessarily be applicable to multimedia processing)
  8. A practical guide to legal issues would not be amiss
  9.  ???

  What other items count as “something multimedia-related that every programmer should know” ?

• current version of ffmpeg3.3.2 encode twice time of my video,the duration last two times long

  20 juin 2017, par jimmy

  I have a video with 00:01:41.46 play time,and transcode it perfect with ffmpeg-2.1.1,but when I upgrade FFmpeg version to 3.3.2 and compile it with the same compile option and same transcode option as 2.1.1 version used, I got a video with 00:03:21.82 long, I played that video to see what was added after 1:41.46, and find that it just repeat the video from the beginning with no audio, I find out no idea to this issue, it seems to be a bug that FFmpeg introducing, anyone help me !

  here is the log that I had transcoded with ffmpeg 3.3.2 :

  ffmpeg -i natural.mp4 -c:v libx264 -c:a copy output.mp4
  
  ffmpeg version 3.3.2 Copyright (c) 2000-2017 the FFmpeg developers
  
  built with gcc 4.6 (Ubuntu/Linaro 4.6.4-6ubuntu2)
  
  
  
  configuration: --enable-gpl --enable-nonfree --yasmexe=release/bin/yasm -- prefix=release --cc= --enable-static --disable-shared --disable-debug --extra-cflags=-Irelease/include --extra-ldflags='-Lrelease/lib -lm -ldl' --disable-ffplay --disable-ffprobe --disable-ffserver --disable-doc --enable-postproc --enable-bzlib --enable-zlib --enable-parsers --enable-libx264 --enable-libmp3lame --enable-libfdk-aac --enable-libspeex --enable-pthreads --extra->libs=-lpthread --enable-encoders --enable-decoders --enable-avfilter --enable->muxers --enable-demuxers
  
  
  
  libavutil      55. 58.100 / 55. 58.100
  
  libavcodec     57. 89.100 / 57. 89.100
  
  libavformat    57. 71.100 / 57. 71.100
  
  libavdevice    57.  6.100 / 57.  6.100
  
  libavfilter     6. 82.100 /  6. 82.100
  
  libswscale      4.  6.100 /  4.  6.100
  
  libswresample   2.  7.100 /  2.  7.100
  
  libpostproc    54.  5.100 / 54.  5.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'natural.mp4':
  
    Metadata:
  
    major_brand     : mp42
  
    minor_version   : 0
  
    compatible_brands: mp42isom
  
    creation_time   : 2009-07-11T08:32:34.000000Z
  
    encoder         : mp4creator 1.6.1d
  
    Duration: 00:01:41.46, start: 0.000000, bitrate: 9063 kb/s
  
    Stream #0:0(eng): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], 8976 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 2997 tbc (default)
  
  Metadata:
  
      creation_time   : 2009-07-11T08:32:34.000000Z
  
  Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
  Metadata:
  
      creation_time   : 2009-07-11T08:33:09.000000Z
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mpeg4 (native) -> h264 (libx264))
  
    Stream #0:1 -> #0:1 (copy)
  
  Press [q] to stop, [?] for help
  
  [libx264 @ 0x2d951e0] using SAR=4/3
  
  [libx264 @ 0x2d951e0] using cpu capabilities: MMX2 SSE2Fast SSSE3 SSE4.2 AVX AVX2 FMA3 LZCNT BMI2
  
  [libx264 @ 0x2d951e0] profile High, level 4.0
  
  [libx264 @ 0x2d951e0] 264 - core 138 r1+3473M a37a143 - H.264/MPEG-4 AVC codec >- Copyleft 2003-2013 - http://www.videolan.org/x264.html - options: cabac=1 >ref=3 deblock=1:0:0 analyse=0x3:0x113 me=hex subme=7 psy=1 psy_rd=1.00:0.00 >mixed_ref=1 me_range=16 chroma_me=1 trellis=1 8x8dct=1 cqm=0 deadzone=21,11 >fast_pskip=1 chroma_qp_offset=-2 threads=6 lookahead_threads=1 sliced_threads=0 >nr=0 decimate=1 interlaced=0 bluray_compat=0 constrained_intra=0 bframes=3 >b_pyramid=2 b_adapt=1 b_bias=0 direct=1 weightb=1 open_gop=0 weightp=2 >keyint=250 keyint_min=23 scenecut=40 intra_refresh=0 rc_lookahead=40 rc=crf >mbtree=1 crf=23.0 qcomp=0.60 qpmin=0 qpmax=69 qpstep=4 ip_ratio=1.40 aq=1:1.00
  
  Output #0, mp4, to 'output.mp4':
  
  Metadata:
  
    major_brand     : mp42
  
    minor_version   : 0
  
    compatible_brands: mp42isom
  
    encoder         : Lavf57.71.100
  
  Stream #0:0(eng): Video: h264 (libx264) ([33][0][0][0] / 0x0021), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], q=-1--1, 23.98 fps, 24k tbn, 23.98 tbc (default)
  
    Metadata:
  
      creation_time   : 2009-07-11T08:32:34.000000Z
  
      encoder         : Lavc57.89.100 libx264
  
    Side data:
  
      cpb: bitrate max/min/avg: 0/0/0 buffer size: 0 vbv_delay: -1
  
    Stream #0:1(eng): Audio: aac (LC) ([64][0][0][0] / 0x0040), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
    Metadata:
  
      creation_time   : 2009-07-11T08:33:09.000000Z
  
  frame= 4842 fps= 27 q=-1.0 Lsize=  107608kB time=00:03:21.82 
  
  bitrate=4367.8kbits/s speed=1.11x     
  
      video:105973kB audio:1556kB subtitle:0kB other streams:0kB global headers:0kB >muxing overhead: 0.074199%
  
  [libx264 @ 0x2d951e0] frame I:54    Avg QP:19.81  size: 77248
  
  [libx264 @ 0x2d951e0] frame P:3960  Avg QP:22.01  size: 25371
  
  [libx264 @ 0x2d951e0] frame B:828   Avg QP:23.01  size:  4680
  
  [libx264 @ 0x2d951e0] consecutive B-frames: 75.2%  4.6%  4.3% 15.9%
  
  [libx264 @ 0x2d951e0] mb I  I16..4: 17.0% 79.0%  3.9%
  
  [libx264 @ 0x2d951e0] mb P  I16..4:  2.1%  7.8%  0.2%  P16..4: 43.9%  9.7% 6.4%  0.0%  0.0%    skip:29.9%
  
  [libx264 @ 0x2d951e0] mb B  I16..4:  0.2%  1.1%  0.0%  B16..8: 29.2%  1.2%  0.2%  direct: 0.7%  skip:67.3%  L0:49.0% L1:47.7% BI: 3.3%
  
  [libx264 @ 0x2d951e0] 8x8 transform intra:78.1% inter:81.6%
  
  [libx264 @ 0x2d951e0] coded y,uvDC,uvAC intra: 52.3% 66.4% 11.9% inter: 20.5% >24.2% 0.8%
  
  [libx264 @ 0x2d951e0] i16 v,h,dc,p: 32% 22% 28% 18%
  
  [libx264 @ 0x2d951e0] i8 v,h,dc,ddl,ddr,vr,hd,vl,hu: 19% 19% 43%  3%  3%  3%  5%  2%  4%
  
  [libx264 @ 0x2d951e0] i4 v,h,dc,ddl,ddr,vr,hd,vl,hu: 23% 24% 12%  4%  8%  7% 11%  4%  5%
  
  [libx264 @ 0x2d951e0] i8c dc,h,v,p: 50% 23% 23%  4%
  
  [libx264 @ 0x2d951e0] Weighted P-Frames: Y:1.5% UV:0.3%
  
  [libx264 @ 0x2d951e0] ref P L0: 71.9% 17.0%  8.5%  2.5%  0.0%
  
  [libx264 @ 0x2d951e0] ref B L0: 89.7%  9.2%  1.2%
  
  [libx264 @ 0x2d951e0] ref B L1: 97.5%  2.5%
  
  [libx264 @ 0x2d951e0] kb/s:4298.67

  Here is the output when use ffmpeg -i natural.mp4 -c copy out.mp4,the output still last double times long :

  ./ffmpeg -i natural.mp4 -c copy out.mp4
  
  ffmpeg version 3.3.2 Copyright (c) 2000-2017 the FFmpeg developers
  
  built with gcc 4.6 (Ubuntu/Linaro 4.6.4-6ubuntu2)
  
    configuration: --enable-gpl --enable-nonfree --yasmexe=release/bin/yasm --prefix=release --cc= --enable-static --disable-shared --disable-debug --extra-cflags=-Irelease/include --extra-ldflags='-Lrelease/lib -lm -ldl' --disable-ffplay --disable-ffprobe --disable-ffserver --disable-doc --enable-postproc --enable-bzlib --enable-zlib --enable-parsers --enable-libx264 --enable-libmp3lame --enable-libfdk-aac --enable-libspeex --enable-pthreads --extra-libs=-lpthread --enable-encoders --enable-decoders --enable-avfilter --enable-muxers --enable-demuxers
  
    libavutil      55. 58.100 / 55. 58.100
  
    libavcodec     57. 89.100 / 57. 89.100
  
    libavformat    57. 71.100 / 57. 71.100
  
    libavdevice    57.  6.100 / 57.  6.100
  
    libavfilter     6. 82.100 /  6. 82.100
  
    libswscale      4.  6.100 /  4.  6.100
  
    libswresample   2.  7.100 /  2.  7.100
  
    libpostproc    54.  5.100 / 54.  5.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'natural.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: mp42isom
  
      creation_time   : 2009-07-11T08:32:34.000000Z
  
      encoder         : mp4creator 1.6.1d
  
    Duration: 00:01:41.46, start: 0.000000, bitrate: 9063 kb/s
  
      Stream #0:0(eng): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], 8976 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 2997 tbc (default)
  
      Metadata:
  
        creation_time   : 2009-07-11T08:32:34.000000Z
  
      Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
      Metadata:
  
        creation_time   : 2009-07-11T08:33:09.000000Z
  
  Output #0, mp4, to 'out.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: mp42isom
  
      encoder         : Lavf57.71.100
  
      Stream #0:0(eng): Video: mpeg4 (Simple Profile) ( [0][0][0] / 0x0020), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], q=2-31, 8976 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 90k tbc (default)
  
      Metadata:
  
        creation_time   : 2009-07-11T08:32:34.000000Z
  
      Stream #0:1(eng): Audio: aac (LC) ([64][0][0][0] / 0x0040), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
      Metadata:
  
        creation_time   : 2009-07-11T08:33:09.000000Z
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #0:1 -> #0:1 (copy)
  
  Press [q] to stop, [?] for help
  
  frame= 4842 fps=2243 q=-1.0 Lsize=  222944kB time=00:03:21.91 
  
  bitrate=9045.4kbits/s speed=93.5x    
  
  video:221299kB audio:1556kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 0.039627%

  Here is the output what ffmpeg-2.1.1 generate,It’s executed correctly :

  ./ffmpeg -i natural.mp4 -c copy output2.mp4
  
  ffmpeg version 2.1.1 Copyright (c) 2000-2013 the FFmpeg developers
  
    built on Mar 10 2017 13:56:14 with gcc 4.6 (Ubuntu/Linaro 4.6.4-6ubuntu2)
  
    configuration: --enable-gpl --enable-nonfree --yasmexe=release/bin/yasm --prefix=release --cc= --enable-static --disable-shared --disable-debug --extra-cflags='-I${ffmpeg_exported_release_dir}/include' --extra-ldflags='-L${ffmpeg_exported_release_dir}/lib -lm -ldl' --disable-ffplay --disable-ffprobe --disable-ffserver --disable-doc --enable-postproc --enable-bzlib --enable-zlib --enable-parsers --enable-libx264 --enable-libmp3lame --enable-libfdk-aac --enable-libspeex --enable-pthreads --extra-libs=-lpthread --enable-encoders --enable-decoders --enable-avfilter --enable-muxers --enable-demuxers
  
    libavutil      52. 48.101 / 52. 48.101
  
    libavcodec     55. 39.101 / 55. 39.101
  
    libavformat    55. 19.104 / 55. 19.104
  
    libavdevice    55.  5.100 / 55.  5.100
  
    libavfilter     3. 90.100 /  3. 90.100
  
    libswscale      2.  5.101 /  2.  5.101
  
    libswresample   0. 17.104 /  0. 17.104
  
    libpostproc    52.  3.100 / 52.  3.100
  
  [mov,mp4,m4a,3gp,3g2,mj2 @ 0x2d2e900] multiple edit list entries, a/v desync might occur, patch welcome
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'natural.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: mp42isom
  
      creation_time   : 2009-07-11 08:32:34
  
      encoder         : mp4creator 1.6.1d
  
    Duration: 00:01:41.46, start: 0.000000, bitrate: 9063 kb/s
  
      Stream #0:0(eng): Video: mpeg4 (Simple Profile) (mp4v / 0x7634706D), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], 8976 kb/s, 23.98 fps, 23.98 tbr, 90k tbn, 2997 tbc (default)
  
      Metadata:
  
        creation_time   : 2009-07-11 08:32:34
  
      Stream #0:1(eng): Audio: aac (mp4a / 0x6134706D), 44100 Hz, stereo, fltp, 125 kb/s (default)
  
      Metadata:
  
        creation_time   : 2009-07-11 08:33:09
  
  Output #0, mp4, to 'output2.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: mp42isom
  
      encoder         : Lavf55.19.104
  
      Stream #0:0(eng): Video: mpeg4 ( [0][0][0] / 0x0020), yuv420p, 1440x1080 [SAR 4:3 DAR 16:9], q=2-31, 8976 kb/s, 23.98 fps, 90k tbn, 90k tbc (default)
  
      Metadata:
  
        creation_time   : 2009-07-11 08:32:34
  
      Stream #0:1(eng): Audio: aac ([64][0][0][0] / 0x0040), 44100 Hz, stereo, 125 kb/s (default)
  
      Metadata:
  
        creation_time   : 2009-07-11 08:33:09
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (copy)
  
    Stream #0:1 -> #0:1 (copy)
  
  Press [q] to stop, [?] for help
  
  frame= 2421 fps=0.0 q=-1.0 Lsize=  112273kB time=00:01:41.49 bitrate=9062.0kbits/s    
  
  video:110650kB audio:1556kB subtitle:0 global headers:0kB muxing overhead 0.060302%

  Here is the video link

• Some seconds of video getting skipped while using ffmpeg source code [on hold]

  30 juin 2017, par Swapnil Konde

  I am using transcoding.c file of ffmpeg Example for creating chunks of videos in .ts format,

  And we are observing some frames/seconds are skipped from Actual Video.
  Can Anyone point out where exactly we should focus on.
  We are using latest ffmpeg version 3.3.2.
  Sometimes we do get Generic error in an external library error as well in encode_write_frame function.

  Thanks.