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• How AVCodecContext bitrate, framerate and timebase is used when encoding single frame

  28 mars 2023, par Cyrus

  I am trying to learn FFmpeg from examples as there is a tight schedule. The task is to encode a raw YUV image into JPEG format of the given width and height. I have found examples from ffmpeg official website, which turns out to be quite straight-forward. However there are some fields in AVCodecContext that I thought only makes sense when encoding videos(e.g. bitrate, framerate, timebase, gopsize, max_b_frames etc).

  


  I understand on a high level what those values are when it comes to videos, but do I need to care about those when I just want a single image ? Currently for testing, I am just setting them as dummy values and it seems to work. But I want to make sure that I am not making terrible assumptions that will break in the long run.

  


  EDIT :

  


  Here is the code I got. Most of them are copy and paste from examples, with some changes to replace old APIs with newer ones.

  


  #include "thumbnail.h"
#include "libavcodec/avcodec.h"
#include "libavutil/imgutils.h"
#include 
#include 
#include 

void print_averror(int error_code) {
    char err_msg[100] = {0};
    av_strerror(error_code, err_msg, 100);
    printf("Reason: %s\n", err_msg);
}

ffmpeg_status_t save_yuv_as_jpeg(uint8_t* source_buffer, char* output_thumbnail_filename, int thumbnail_width, int thumbnail_height) {
    const AVCodec* mjpeg_codec = avcodec_find_encoder(AV_CODEC_ID_MJPEG);
    if (!mjpeg_codec) {
        printf("Codec for mjpeg cannot be found.\n");
        return FFMPEG_THUMBNAIL_CODEC_NOT_FOUND;
    }

    AVCodecContext* codec_ctx = avcodec_alloc_context3(mjpeg_codec);
    if (!codec_ctx) {
        printf("Codec context cannot be allocated for the given mjpeg codec.\n");
        return FFMPEG_THUMBNAIL_ALLOC_CONTEXT_FAILED;
    }

    AVPacket* pkt = av_packet_alloc();
    if (!pkt) {
        printf("Thumbnail packet cannot be allocated.\n");
        return FFMPEG_THUMBNAIL_ALLOC_PACKET_FAILED;
    }

    AVFrame* frame = av_frame_alloc();
    if (!frame) {
        printf("Thumbnail frame cannot be allocated.\n");
        return FFMPEG_THUMBNAIL_ALLOC_FRAME_FAILED;
    }

    // The part that I don't understand
    codec_ctx->bit_rate = 400000;
    codec_ctx->width = thumbnail_width;
    codec_ctx->height = thumbnail_height;
    codec_ctx->time_base = (AVRational){1, 25};
    codec_ctx->framerate = (AVRational){1, 25};

    codec_ctx->gop_size = 10;
    codec_ctx->max_b_frames = 1;
    codec_ctx->pix_fmt = AV_PIX_FMT_YUV420P;
    int ret = av_image_fill_arrays(frame->data, frame->linesize, source_buffer, AV_PIX_FMT_YUV420P, thumbnail_width, thumbnail_height, 32);
    if (ret < 0) {
        print_averror(ret);
        printf("Pixel format: yuv420p, width: %d, height: %d\n", thumbnail_width, thumbnail_height);
        return FFMPEG_THUMBNAIL_FILL_FRAME_DATA_FAILED;
    }

    ret = avcodec_send_frame(codec_ctx, frame);
    if (ret < 0) {
        print_averror(ret);
        printf("Failed to send frame to encoder.\n");
        return FFMPEG_THUMBNAIL_FILL_SEND_FRAME_FAILED;
    }

    ret = avcodec_receive_packet(codec_ctx, pkt);
    if (ret < 0) {
        print_averror(ret);
        printf("Failed to receive packet from encoder.\n");
        return FFMPEG_THUMBNAIL_FILL_SEND_FRAME_FAILED;
    }

    // store the thumbnail in output
    int fd = open(output_thumbnail_filename, O_CREAT | O_RDWR);
    write(fd, pkt->data, pkt->size);
    close(fd);

    // freeing allocated structs
    avcodec_free_context(&codec_ctx);
    av_frame_free(&frame);
    av_packet_free(&pkt);
    return FFMPEG_SUCCESS;
}


  


• No such file or directory : 'ffprobe' : 'ffprobe'

  27 novembre 2023, par Jack McCumber

  I'm hoping someone can point me in the right direction. I'm currently trying to build a python GUI that plays clips of sounds from a specified file and allows the user to annotate it. All the research I've done has pointed my to using pydub. I'm using the following snippet :

  


  from pydub import AudioSegment
from pydub.playback import play

song = AudioSegment.from_wav("beepboop.mp3")
play(song)


  


  However, I'm currently getting the following error :

  


  Warning (from warnings module):&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/pydub/utils.py", line 170&#xA;    warn("Couldn&#x27;t find ffmpeg or avconv - defaulting to ffmpeg, but may not work", RuntimeWarning)&#xA;RuntimeWarning: Couldn&#x27;t find ffmpeg or avconv - defaulting to ffmpeg, but may not work&#xA;&#xA;Warning (from warnings module):&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/pydub/utils.py", line 198&#xA;    warn("Couldn&#x27;t find ffprobe or avprobe - defaulting to ffprobe, but may not work", RuntimeWarning)&#xA;RuntimeWarning: Couldn&#x27;t find ffprobe or avprobe - defaulting to ffprobe, but may not work&#xA;Traceback (most recent call last):&#xA;  File "/Users/jack/Desktop/code-repo/convert-csv-to-json/cleaner.py", line 7, in <module>&#xA;    song = AudioSegment.from_wav("beepboop.mp3")&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/pydub/audio_segment.py", line 808, in from_wav&#xA;    return cls.from_file(file, &#x27;wav&#x27;, parameters=parameters)&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/pydub/audio_segment.py", line 728, in from_file&#xA;    info = mediainfo_json(orig_file, read_ahead_limit=read_ahead_limit)&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages/pydub/utils.py", line 274, in mediainfo_json&#xA;    res = Popen(command, stdin=stdin_parameter, stdout=PIPE, stderr=PIPE)&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/subprocess.py", line 775, in __init__&#xA;    restore_signals, start_new_session)&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/subprocess.py", line 1522, in _execute_child&#xA;    raise child_exception_type(errno_num, err_msg, err_filename)&#xA;FileNotFoundError: [Errno 2] No such file or directory: &#x27;ffprobe&#x27;: &#x27;ffprobe&#x27;&#xA;</module>

  


  I've downloaded both ffprobe and ffmpeg from the official website, extracted the files, and installed to usr/local/bin based on input I've read in other StackOverflow comments. When I run :

  


  print(os.environ['PATH'])


  


  I get :

  


  /usr/bin:/bin:/usr/sbin:/sbin


  


  Also, MacOSX won't let me manually drag the executable into /usr/bin or /usr/sbin. Nor will it let me copy it into the directory using :

  


  $ sudo cp ffmpeg /usr/bin


  


  When I use :

  


  pip3 install ffprobe-python


  


  I get :

  


  Requirement already satisfied: ffprobe-python in /Library/Frameworks/Python.framework/Versions/3.7/lib/python3.7/site-packages (1.0.3)


  


  I'll add that when I try and use the "apt install" method, it barks at me and says my version of MacOSX isn't supported.

  


• Slowing down 960 fps video with ffmpeg (setpts is not working)

  7 novembre 2016, par haridsv

  I am trying to slow down a video recorded on an Android phone at 960fps. I found a lot of previous posts and blogs that all basically say the same thing, that you need to change the "presentation timestamp" (pts). I also found the official documentation that is saying the same thing. The command-line basically looks like this :

  ffmpeg -i input.mp4 -filter:v "setpts=4*PTS" -r 30 -y output.mp4

  I copied the video file using Android Filter Transfer and when I use the above command-line, it works to slow it down, but the resulting output is choppy. The output of the ffmpeg also indicates that it is duplicating the frames :

  frame=  687 fps=103 q=-1.0 Lsize=    4454kB time=00:00:22.80 bitrate=1600.1kbits/s dup=515 drop=0 speed=3.42x

  Running ffprobe on the file shows this :

  ffprobe version 3.1.1 Copyright (c) 2007-2016 the FFmpeg developers
  
    built with Apple LLVM version 7.3.0 (clang-703.0.31)
  
    configuration: --prefix=/usr/local/Cellar/ffmpeg/3.1.1 --enable-shared --enable-pthreads --enable-gpl --enable-version3 --enable-hardcoded-tables --enable-avresample --cc=clang --host-cflags= --host-lda
  
    libavutil      55. 28.100 / 55. 28.100
  
    libavcodec     57. 48.101 / 57. 48.101
  
    libavformat    57. 41.100 / 57. 41.100
  
    libavdevice    57.  0.101 / 57.  0.101
  
    libavfilter     6. 47.100 /  6. 47.100
  
    libavresample   3.  0.  0 /  3.  0.  0
  
    libswscale      4.  1.100 /  4.  1.100
  
    libswresample   2.  1.100 /  2.  1.100
  
    libpostproc    54.  0.100 / 54.  0.100
  
  Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'VID_20161030_213810.mp4':
  
    Metadata:
  
      major_brand     : mp42
  
      minor_version   : 0
  
      compatible_brands: isommp42
  
      creation_time   : 2016-10-30 16:08:14
  
      location        : +17.3874+078.3395/
  
      location-eng    : +17.3874+078.3395/
  
      com.android.version: 6.0.1
  
      com.android.capture.fps: 120.000000
  
    Duration: 00:00:05.73, start: 0.000000, bitrate: 14991 kb/s
  
      Stream #0:0(eng): Video: h264 (Baseline) (avc1 / 0x31637661), yuv420p, 1280x720, 13859 kb/s, SAR 1:1 DAR 16:9, 30 fps, 30 tbr, 90k tbn, 180k tbc (default)
  
      Metadata:
  
        creation_time   : 2016-10-30 16:08:14
  
        handler_name    : VideoHandle

  This seems to detect that the video is 30 fps instead of 960 fps, which is probably why it is filling in with duplicate frames instead of using the existing frames.

  I recording the video on Lenovo Z2 Plus (AKA Zuk Z2). If I playback the video using the built-in player at a slow speed it looks extremely smooth, so the frames are definitely there. Could someone help me figure out the right way ? The file is available here (about 10MB), in case someone would like to try it.

  Update : Video playback at slo-mo on the phone recorded with another phone. Notice how smooth and slow the sparks are thrown around, which is impossible if the original video is 30fps.

  • Slow-mo clip 1
  • Slow-mo click 2
  • Full video played in slow-mo (47s, probably at 120fps)