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• python imageio.get_reader() returns format error

  19 août 2020, par tristan_jia

  import imageio

reader = imageio.get_reader("./t.mp4")


  


  As shown above, with python 3.6.10, it returns :

  


  >>> reader = imageio.get_reader("../")&#xA;Traceback (most recent call last):&#xA;  File "<stdin>", line 1, in <module>&#xA;  File "/home/tristan_jia/workspace/py3.6/venv/lib/python3.6/site-packages/imageio/core/functions.py", line 129, in get_reader&#xA;    return format.get_reader(request)&#xA;  File "/home/tristan_jia/workspace/py3.6/venv/lib/python3.6/site-packages/imageio/core/format.py", line 168, in get_reader&#xA;    return self.Reader(self, request)&#xA;  File "/home/tristan_jia/workspace/py3.6/venv/lib/python3.6/site-packages/imageio/core/format.py", line 217, in __init__&#xA;    self._open(**self.request.kwargs.copy())&#xA;  File "/home/tristan_jia/workspace/py3.6/venv/lib/python3.6/site-packages/imageio/plugins/ffmpeg.py", line 357, in _open&#xA;    self._initialize()&#xA;  File "/home/tristan_jia/workspace/py3.6/venv/lib/python3.6/site-packages/imageio/plugins/ffmpeg.py", line 430, in _initialize&#xA;    shell=ISWIN)&#xA;  File "/usr/lib64/python3.6/subprocess.py", line 729, in __init__&#xA;    restore_signals, start_new_session)&#xA;  File "/usr/lib64/python3.6/subprocess.py", line 1364, in _execute_child&#xA;    raise child_exception_type(errno_num, err_msg, err_filename)&#xA;OSError: [Errno 8] Exec format error: &#x27;/home/tristan_jia/.imageio/ffmpeg/ffmpeg-linux64-v3.3.1&#x27;&#xA;&#xA;</module></stdin>

  


  I searched everywhere but haven't seen any similar questions. The script runs on Opensuse Leap 15.1, is it related to the system I use ?

  


• How do I play back video on Android with custom playback speed ?

  13 novembre 2015, par guidow

  I want to play back a video in Android, rendering it to a SurfaceTexture or something else that is usable as an OpenGL ES texture, but I need very precise control over the playback speed of the video to synchronize it to a stream of external events. These events will happen at a roughly predictable speed, but the exact speed will depend on many small mechanical details, influenced by many small factors, including the weather (and possibly even the phase of the moon...).

  The android.media.MediaPlayer class provided by android allows rendering to a SurfaceTexture (and the 360Videos app from the Oculus Mobile SDK successfully uses that feature), but unfortunately does not seem to allow altering the playback speed, at least not as far as I could tell from the documentation here.

  I have tried pausing and resuming the playback using pause() and start() respectively, to influence the playback speed, but that leads to extremely choppy and slow playback. My idea here was to make the video have a higher framerate than would ever be needed, and to then manually retard every frame until it actually needs to be shown. From the messages in the log, it looks to me like the MediaPlayer class will release various needed resources on pause and rerequest them on resume, which obviously kills performance if you do that once per frame.

  Another option I am looking at is ffmpeg. This one seems like it will do what i want, it doesn’t do any timings itself, it just decodes frames whenever I tell it to to a buffer, leaving me to use it however I want, whenever I want. The obvious drawback is that ffmpeg, at least on android, doesn’t do hardware decoding and probably won’t be able to decode 4K media in realtime.

  Yet another thing I was looking at was OpenMAX AL. Unfortunately, OpenMax AL is pretty hard to get into. I haven’t found any good beginner’s documentation yet, only some old, maybe outdated, READMEs as well as the interface specification from Khronos. The latter is a very long and cumbersome read, though, and I couldn’t yet even figure out if OpenMAX AL will even allow me to do my own timings...

• FFmpeg hangs on buffer fill c++

  2 mars 2021, par Derek Halden

  I'm processing a bunch of frames from an RTSP stream using ffmpeg. I end up doing a lot of processing on these frames, which means that I'm not always pulling in real-time. If the buffer gets full, the process hangs. I'm wondering if one of the following solutions is feasible/fixes the problem, and if so, how I would implement it using the ffmpeg libraries :

  



  1) Is there a way to clear the buffer if I ever reach a point where it's hanging ? (I can determine when it's hung, I just don't know what to do about it).

  



  2) Is there a way to make the buffer overwrite the old data, and just always read the most recent data ? It doesn't matter to me if I lose frames.

  



  3) I've already discovered that I can make the buffer arbtrarily large with : av_dict_set(&avd, "buffer_size", "655360", 0);. This could be a solution, but I don't know how large/small it needs to be, because I don't know how long the stream will post video for ?

  



  4) Is this just a bug that I need to bring up with the ffmpeg people ?

  



  5) Something else I haven't considered ?

  



  while(av_read_frame(context, &(packet)) >= 0 && fcount < fps*SECONDS) {
    clock_t start, end;
    int ret = avcodec_send_packet(codec_context, packet);
    if(!(packet->stream_index == video_stream_index)) {
      continue;
    }

    if (ret == AVERROR(EAGAIN) || ret == AVERROR(EINVAL)) {
      continue;
    } else if (ret < 0) {
      cerr << "Error while decoding frame " << fcount << endl;
      exit(1);
    }

    ret = avcodec_receive_frame(codec_context, frame);
    if (ret == AVERROR(EAGAIN) || ret == AVERROR(EINVAL)) {
      continue;
    } else if (ret < 0) {
      cerr << "Error while decoding frame " << fcount << endl;
      exit(1);
    }

    sws_scale(img_convert_ctx, frame->data, frame->linesize, 0,
              codec_context->height, picture_rgb->data, picture_rgb->linesize);

    if(!frame) {
      cerr << "Could not allocate video frame" << endl;
      exit(1);
    }

    if(codec_context == NULL) {
      cerr << "Cannot initialize the conversion context!" << endl;
      exit(1);
    }

    // Do something with the frame here

    fcount++;
    av_packet_unref(&(packet));

}


  



  I have added the code that causes the program to hang.