Recherche avancée

Sur d’autres sites (12402)

• How to build list of tasks for asyncio.gather in Python 3.8

  22 juillet 2020, par mcgregor94086

  Below I have attached a test program to demonstrate a problem I am having with asyncio.gather throwing a TypeError.

  


  My objective : To make multiple concurrent asynchronous calls to capture camera images to files from an array of USB cameras attached to my computer. When all cameras have completed their async captures, I want then resume processing.

  


  The async coroutine take_image() shown here makes a system call to the "ffmpeg" application that captures an image from the specified camera to a specified file.

  


  import asyncio
import os
import subprocess
import time

async def take_image(camera_id, camera_name, image_file_path, image_counter):
    image_capture_tic = time.perf_counter()
    try:
        run_cmd = subprocess.run( ["ffmpeg", '-y', '-hide_banner', '-f', 'avfoundation', '-i', camera_id,
                                   '-frames:v', '1', '-f', 'image2', image_file_path], universal_newlines=True,
                                 stdout=subprocess.PIPE, stderr=subprocess.PIPE)  # Note, ffmpeg writes to stderr, not stdout!
    except Exception as e:
        print("Error: Unable to capture image for", image_file_path)
        return "NO IMAGE!"

    image_capture_toc = time.perf_counter()
    print(f"{image_counter}: Captured {camera_name} image in: {image_capture_toc - image_capture_tic:0.0f} seconds")
    return camera_name


  


  The main() routine shown below takes a list of multiple cameras, and iterating over each camera in the list, main() makes creates an asyncio task for each camera using asyncio.create_task(). Each task is added to a list of tasks.

  


  Once all image capture tasks have been started, I await their completion using await asyncio.gather(tasks).

  


  async def main():
    tic = time.perf_counter()
    camera_list = [('0', 'FHD Camera #1'),  ('1', 'FHD Camera #2'), ('2', 'FHD Camera #3'), ]
    image_counter = 1
    tasks = []
    for camera_pair in camera_list:
        camera_id, camera_name = camera_pair
        image_file_name = 'img' + str(image_counter) + "-cam" + str(camera_id)  + "-" + camera_name + '.jpg'
        image_file_path = os.path.join("/tmp/test1/img", image_file_name)

        # schedule all image captures calls *concurrently*:
        tasks.append(asyncio.create_task(take_image(camera_id, camera_name, image_file_path, image_counter),
                     name=image_file_name))
        image_counter = image_counter + 1

    await asyncio.gather(tasks) # <-- This line throws a TypeError!
    toc = time.perf_counter()
    print(f"Captured list of {image_counter - 1} cameras in: {toc - tic:0.0f} seconds")

asyncio.run(main())


  


  Unfortunately, when I attempt to run this program, I am getting this error :

  


  TypeError : unhashable type : 'list'

  


  and the following Traceback :

  


  Traceback (most recent call last):&#xA;  File "scratch_10.py", line 41, in <module>&#xA;    asyncio.run(main())&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/runners.py", line 43, in run&#xA;    return loop.run_until_complete(main)&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/base_events.py", line 608, in run_until_complete&#xA;    return future.result()&#xA;  File "scratch_10.py", line 36, in main&#xA;    await asyncio.gather(tasks)&#xA;  File "/Library/Frameworks/Python.framework/Versions/3.8/lib/python3.8/asyncio/tasks.py", line 805, in gather&#xA;    if arg not in arg_to_fut:&#xA;TypeError: unhashable type: &#x27;list&#x27;&#xA;</module>

  


  I have been trying to puzzle through the 3.8 documentation on asyncio, but I don't understand what is wrong.

  


  How can I have each take_image request run asynchronously, and then resume processing in my calling routine once each task is complete ?

  


• Getting List of default argument values if not used in FFMPEG command execution

  12 juillet 2020, par Pradeep Prabhu

  When I use FFMPEG to capture a live IPTV stream on my MAC, I generally end up with an interrupted video. When I send these four arguments, the capture is successful.

  


  -reconnect 1 -reconnect_at_eof 1 -reconnect_streamed 1 -reconnect_delay_max 2

  


  I don't want to specify these arguments everytime, So I decided to update the default values in the source code. Unsure if I have done it right - I updated http.c which contains these arguments. I re-compiled FFMPEG successfully.

  


  I want to know if my changes are applied. Is there a way I can list out all the default values of the arguments. I can use this compiled version of FFMPEG for a week, and determine if the fix is applied or not, I was wondering, if there is a quicker and easier way to do it.

  


  If this is successful, I can use this version of FFMPEG for Emby & TellyTV.

  


• av_hwdevice_iterate_types returns an empty list

  9 juillet 2020, par Ruslan Ablyazov

  I used an example https://github.com/FFmpeg/FFmpeg/blob/master/doc/examples/hw_decode.c

  


  The av_hwdevice_iterate_types function returns an empty list. What could be the reason ?

  


  And avcodec_find_decoder_by_name("h264_cuvid") returns NULL.

  


  FFmpeg version :

  


  ffmpeg version 4.3 Copyright (c) 2000-2020 the FFmpeg developers
built with gcc 8 (Debian 8.3.0-6)
configuration: --enable-gpl --enable-ladspa --enable-libpulse --enable-libsoxr --enable-libspeex --enable-avfilter --enable-avresample --enable-postproc --enable-pthreads --enable-libass --enable-libfreetype --enable-libmp3lame --enable-libx264 --enable-libx265 --enable-nonfree --disable-ffplay --enable-libxvid --enable-cuda --enable-cuda-nvcc --enable-cuvid --enable-nvenc --enable-nonfree --enable-libnpp --extra-cflags=-I/usr/local/cuda/include --extra-ldflags=-L/usr/local/cuda/lib64
libavutil 56. 51.100 / 56. 51.100
libavcodec 58. 91.100 / 58. 91.100
libavformat 58. 45.100 / 58. 45.100
libavdevice 58. 10.100 / 58. 10.100
libavfilter 7. 85.100 / 7. 85.100
libavresample 4. 0. 0 / 4. 0. 0
libswscale 5. 7.100 / 5. 7.100
libswresample 3. 7.100 / 3. 7.100
libpostproc 55. 7.100 / 55. 7.100


  


  The command ffmpeg -c:v h264_cuvid -i 7.mp4 71.mp4 outputs :

  


  ...
Stream mapping:
Stream #0:0 -> #0:0 (h264 (h264_cuvid) -> h264 (libx264))
....


  


  And it works.

  


  The command ffmpeg-hwaccel cuda-i 7.mp4 71.mp4 outputs :

  


  ...
Stream mapping:
Stream #0:0 -> #0:0 (h264 (native) -> h264 (libx264))
....


  


  The command ffmpeg -codecs outputs :

  


   ...
 DEV.LS h264                 H.264 / AVC / MPEG-4 AVC / MPEG-4 part 10 (decoders: h264 h264_v4l2m2m h264_cuvid ) (encoders: libx264 libx264rgb h264_nvenc h264_v4l2m2m nvenc nvenc_h264 )
 D.VIL. hap                  Vidvox Hap
 DEV.L. hevc                 H.265 / HEVC (High Efficiency Video Coding) (decoders: hevc hevc_v4l2m2m hevc_cuvid ) (encoders: libx265 nvenc_hevc hevc_nvenc hevc_v4l2m2m )
 ...