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• ffmpeg : programmatically use libavcodec and encode and decode raw bitmap, all in just few milliseconds and small compressed size on Raspberry Pi 4

  15 mars 2023, par Jerry Switalski

  We need to compress the size of the 1024x2048 image we produce, to size of about jpeg (200-500kb) from raw 32bits RGBA (8Mb) on Raspberry Pi 4. All in c/c++ program.

  


  The compression needs to be just in few milliseconds, otherwise it is pointless to us.

  


  We decided to try supported encoding using ffmpeg dev library and c/c++ code.

  


  The problem we are facing is that when we edited example of the encoding, provided by ffmpeg developers, the times we are dealing are unacceptable.

  


  Here you can see the edited code where the frames are created :

  


  for (i = 0; i < 25; i++)
{
#ifdef MEASURE_TIME
        auto start_time = std::chrono::high_resolution_clock::now();
        std::cout << "START Encoding frame...\n";
#endif
    fflush(stdout);

    ret = av_frame_make_writable(frame);
    if (ret < 0)
        exit(1);

    //I try here, to convert our 32 bits RGBA image to YUV pixel format:

    for (y = 0; y < c->height; y++)
    {
        for (x = 0; x < c->width; x++)
        {
            int imageIndexY = y * frame->linesize[0] + x;

            uint32_t rgbPixel = ((uint32_t*)OutputDataImage)[imageIndexY];

            double Y, U, V;
            uint8_t R = rgbPixel << 24;
            uint8_t G = rgbPixel << 16;
            uint8_t B = rgbPixel << 8;

            YUVfromRGB(Y, U, V, (double)R, (double)G, (double)B);
            frame->data[0][imageIndexY] = (uint8_t)Y;

            if (y % 2 == 0 && x % 2 == 0)
            {
                int imageIndexU = (y / 2) * frame->linesize[1] + (x / 2);
                int imageIndexV = (y / 2) * frame->linesize[2] + (x / 2);

                frame->data[1][imageIndexU] = (uint8_t)U;
                frame->data[2][imageIndexV] = (uint8_t)Y;
            }
        }
    }

    frame->pts = i;

    /* encode the image */
    encode(c, frame, pkt, f);

#ifdef MEASURE_TIME
        auto end_time = std::chrono::high_resolution_clock::now();
        auto time = end_time - start_time;
        std::cout << "FINISHED Encoding frame in: " << time / std::chrono::milliseconds(1) << "ms.\n";

#endif
    }


  


  Here are some important parts of the previous parts of that function :

  


  codec_name = "mpeg4";

codec = avcodec_find_encoder_by_name(codec_name);

c = avcodec_alloc_context3(codec);
    
c->bit_rate = 1000000;  
c->width = IMAGE_WIDTH;
c->height = IMAGE_HEIGHT;
c->gop_size = 1;
c->max_b_frames = 1;
c->pix_fmt = AV_PIX_FMT_YUV420P;   


  


  IMAGE_WIDTH and IMAGE_HEIGHT are 1024 and 2048 corresponding.

  


  The result I have ran on Raspberry Pi 4 look like this :

  


  START Encoding frame...
Send frame   0
FINISHED Encoding frame in: 40ms.
START Encoding frame...
Send frame   1
Write packet   0 (size=11329)
FINISHED Encoding frame in: 60ms.
START Encoding frame...
Send frame   2
Write packet   1 (size=11329)
FINISHED Encoding frame in: 58ms.


  


  Since I am completely green in encoding and using codecs, my question will be how to do it the best way and correct way, meaning the way which would reduce timing to few ms, and I am not sure the codec was chosen the best for the job, or the pixel format.

  


  The rest of the meaningful code you can see here (the encode() function you can find in the ffmpeg developer example I gave link to above) :

  


  void RGBfromYUV(double& R, double& G, double& B, double Y, double U, double V)
{
    Y -= 16;
    U -= 128;
    V -= 128;
    R = 1.164 * Y + 1.596 * V;
    G = 1.164 * Y - 0.392 * U - 0.813 * V;
    B = 1.164 * Y + 2.017 * U;
}


  


• How do I remux/transcode a progressive file in ffmpeg ?

  3 décembre 2014, par Levi Roberts

  Here’s what I’m trying to do.

  My primary objective is to remux or transcode a currently downloading media file for AppleTV and iOS compatible streaming.

  I am doing this by looking at the media file and only transcoding when necessary, otherwise it will only alter the container the video/audio lives in. This will reduce overhead for files that are already compatible. The specific compatible output I am looking for is AppleTV3 and iOS.

  I have a file that is progressive, meaning that it is downloading using another download manager or another app without the help of nodejs. This file may or may not have the moov information available in the beginning of the file. It just so happens, that I believe my test file does.

  I have some code that is partially working and it would make sense to be able to get this code fully working. That said, I’m not dismissing alternative ways to do this.

  My primary problem (I think) has to do with the moov header location or that it’s being set incorrectly. I’m hoping the fix is as simple as correcting my poor ffmpeg knowledge with command line parameters.

  I am piping the file to and from ffmpeg via GrowingFile and fs.createWriteStream respectively.

  My code for doing so is :

  var fs = require('fs');
  
  var child = require('child_process');
  
  
  
  var GrowingFile = require('growing-file');
  
  var input_file = GrowingFile.open('./tmp/input.mp4');
  
  var output_file = fs.createWriteStream('./tmp/output.m4v');
  
  
  
  // I've tried various args and ffmpeg params here without success.
  
  var args = ['-re', '-i', 'pipe:0', '-g', '52', '-ab', '64k', '-vcodec', 'libx264', '-vb', '448k', '-f', 'mp4', '-movflags', 'frag_keyframe+faststart', 'pipe:1'];
  
  var trans_proc = child.spawn('ffmpeg', args, null); 
  
  
  
  input_file.pipe(trans_proc.stdin);
  
  trans_proc.stdout.pipe(output_file);

  I am also temporarily trying to make these files work as intended via ffmpeg command line alone, without success. That command is :

  ffmpeg -i original.mp4 -vcodec copy -r 24 output.m4v

  Snippet of original.mp4 via mediainfo :

  General
  
  Format                                   : MPEG-4
  
  Format profile                           : Base Media / Version 2
  
  Codec ID                                 : mp42
  
  File size                                : 9.87 MiB
  
  Duration                                 : 43mn 14s
  
  Overall bit rate mode                    : Variable
  
  Overall bit rate                         : 31.9 Kbp
  
  
  
  Video
  
  Format                                   : AVC
  
  Format/Info                              : Advanced Video Codec
  
  Format profile                           : High@L2.1
  
  Codec ID                                 : avc1
  
  Duration                                 : 43mn 14s
  
  Width                                    : 480 pixels
  
  Height                                   : 268 pixels
  
  Color space                              : YUV
  
  Scan type                                : Progressive
  
  Stream size                              : 67.5 MiB
  
  
  
  Audio
  
  Format                                   : AAC
  
  Format/Info                              : Advanced Audio Codec
  
  Format profile                           : LC
  
  Codec ID                                 : 40
  
  Duration                                 : 43mn 14s
  
  Bit rate mode                            : Variable
  
  Bit rate                                 : 96.0 Kbps

  What’s happening is that output.m4v has an incorrect duration of only the part of the file that’s already downloaded. The video reaches the end or a refresh happens to make the duration longer. This process repeats until the original file is done downloading. What I want is to be able to emulate/clone the duration of the input file to the output file .

• FFmpeg meaningful video thumbnails

  18 avril 2015, par Maverick

  I know this question has been discussed already here. However, it did not solve the problem completely. I trying to retrieve meaning thumbnails from video and while executing the following command.

  ffmpeg -ss 3 -i input.avi -vf "select=gt(scene\,0.4)" -frames:v 5 -vsync vfr -vf "fps=fps=1/600" out%02d.jpg

  As a result, I am only able to get 1 image out of this video. I am not sure, what is going wrong over here.

  Also, it would be great, if someone kindly give a quick explanation of this command parameters and filters. The command originally comes from here

  FFMPEG console output :

  ffmpeg version 2.6 Copyright (c) 2000-2015 the FFmpeg developers
  
    built with Apple LLVM version 6.0 (clang-600.0.57) (based on LLVM 3.5svn)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/2.6 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-ldflags= --enable-libx264 --enable-libmp3lame --enable-libvo-aacenc --enable-libxvid --enable-libfreetype --enable-libtheora --enable-libvorbis --enable-libvpx --enable-librtmp --enable-libopencore-amrnb --enable-libopencore-amrwb --enable-libass --enable-ffplay --enable-libspeex --enable-libschroedinger --enable-libfdk-aac --enable-libopus --enable-frei0r --enable-libopenjpeg --disable-decoder=jpeg2000 --extra-cflags='-I/usr/local/Cellar/openjpeg/1.5.1_1/include/openjpeg-1.5 ' --enable-nonfree --enable-vda
  
    libavutil      54. 20.100 / 54. 20.100
  
    libavcodec     56. 26.100 / 56. 26.100
  
    libavformat    56. 25.101 / 56. 25.101
  
    libavdevice    56.  4.100 / 56.  4.100
  
    libavfilter     5. 11.102 /  5. 11.102
  
    libavresample   2.  1.  0 /  2.  1.  0
  
    libswscale      3.  1.101 /  3.  1.101
  
    libswresample   1.  1.100 /  1.  1.100
  
    libpostproc    53.  3.100 / 53.  3.100
  
  Input #0, avi, from 'tagesschau.avi':
  
    Metadata:
  
      encoder         : Lavf56.25.101
  
    Duration: 00:00:20.03, start: 0.000000, bitrate: 4357 kb/s
  
      Stream #0:0: Video: mpeg4 (Simple Profile) (xvid / 0x64697678), yuv420p, 720x540 [SAR 1:1 DAR 4:3], 4190 kb/s, 29.97 fps, 29.97 tbr, 29.97 tbn, 29.97 tbc
  
      Stream #0:1: Audio: ac3 ([0] [0][0] / 0x2000), 44100 Hz, stereo, fltp, 160 kb/s
  
  [swscaler @ 0x7fcb2a00f600] deprecated pixel format used, make sure you did set range correctly
  
  [mjpeg @ 0x7fcb2a803c00] bitrate tolerance 4000000 too small for bitrate 200000, overriding
  
  Output #0, image2, to 'out%02d.jpg':
  
    Metadata:
  
      encoder         : Lavf56.25.101
  
      Stream #0:0: Video: mjpeg, yuvj420p(pc), 720x540 [SAR 1:1 DAR 4:3], q=2-31, 200 kb/s, 0k fps, 0k tbn, 0k tbc
  
      Metadata:
  
        encoder         : Lavc56.26.100 mjpeg
  
  Stream mapping:
  
    Stream #0:0 -> #0:0 (mpeg4 (native) -> mjpeg (native))
  
  Press [q] to stop, [?] for help
  
  frame=    1 fps=0.0 q=6.9 Lsize=N/A time=00:10:00.00 bitrate=N/A    
  
  video:44kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown