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• How extract JPEG image from H264 stream in constant time

  27 août 2021, par Ross Gardiner

  I want to extract a JPEG frame from a H264 stream on disk. The extraction needs to be as fast as possible for my real-time requirements.

  


  Until now I have been using ffmpeg-python lib which is just a python wrapper for ffmpeg. Here is a code snippet :

  


  out, _ = (
    ffmpeg
    .input('./5sec.h264')
    .filter('select', 'gte(n,{})'.format(144))
    .output('pipe:', vframes=1, format='image2', vcodec='h264')
    .run(capture_stdout=True)
)


  


  This outputs the jpeg to stdout, with some effort I could read this into my program.

  


  However, as I use larger and larger stream files the extraction time to grab the JPEG increases. I thought lookup time would be constant as ffmpeg is highly optimised ?

  


  Is there a constant time solution to lookup and return a frame from a h264 (or even mjpeg) format stream on disk ?

  


  Edit :
Heres the command I use without the python wrapper :
ffmpeg -i 5sec.h264 -frames:v 1 -filter:v "select=gte(n\,25)" -f image2 frame.jpg

  


  here's output :

  


  ffmpeg version 4.1.6-1~deb10u1+rpt2 Copyright (c) 2000-2020 the FFmpeg developers
  built with gcc 8 (Raspbian 8.3.0-6+rpi1)
  configuration: --prefix=/usr --extra-version='1~deb10u1+rpt2' --toolchain=hardened --incdir=/usr/include/arm-linux-gnueabihf --enable-gpl --disable-stripping --enable-avresample --disable-filter=resample --enable-avisynth --enable-gnutls --enable-ladspa --enable-libaom --enable-libass --enable-libbluray --enable-libbs2b --enable-libcaca --enable-libcdio --enable-libcodec2 --enable-libflite --enable-libfontconfig --enable-libfreetype --enable-libfribidi --enable-libgme --enable-libgsm --enable-libjack --enable-libmp3lame --enable-libmysofa --enable-libopenjpeg --enable-libopenmpt --enable-libopus --enable-libpulse --enable-librsvg --enable-librubberband --enable-libshine --enable-libsnappy --enable-libsoxr --enable-libspeex --enable-libssh --enable-libtheora --enable-libtwolame --enable-libvidstab --enable-libvorbis --enable-libvpx --enable-libwavpack --enable-libwebp --enable-libx265 --enable-libxml2 --enable-libxvid --enable-libzmq --enable-libzvbi --enable-lv2 --enable-omx --enable-openal --enable-opengl --enable-sdl2 --enable-omx-rpi --enable-mmal --enable-neon --enable-rpi --enable-vout-drm --enable-v4l2-request --enable-libudev --enable-libdc1394 --enable-libdrm --enable-libiec61883 --enable-chromaprint --enable-frei0r --enable-libx264 --enable-shared --libdir=/usr/lib/arm-linux-gnueabihf --cpu=arm1176jzf-s --arch=arm
  libavutil      56. 22.100 / 56. 22.100
  libavcodec     58. 35.100 / 58. 35.100
  libavformat    58. 20.100 / 58. 20.100
  libavdevice    58.  5.100 / 58.  5.100
  libavfilter     7. 40.101 /  7. 40.101
  libavresample   4.  0.  0 /  4.  0.  0
  libswscale      5.  3.100 /  5.  3.100
  libswresample   3.  3.100 /  3.  3.100
  libpostproc    55.  3.100 / 55.  3.100
Input #0, h264, from '5sec.h264':
  Duration: N/A, bitrate: N/A
    Stream #0:0: Video: h264 (High), yuv420p(progressive), 640x480, 25 fps, 25 tbr, 1200k tbn, 50 tbc
Stream mapping:
  Stream #0:0 -> #0:0 (h264 (native) -> mjpeg (native))
Press [q] to stop, [?] for help
[swscaler @ 0x1a25390] deprecated pixel format used, make sure you did set range correctly
Output #0, image2, to 'frame.jpg':
  Metadata:
    encoder         : Lavf58.20.100
    Stream #0:0: Video: mjpeg, yuvj420p(pc), 640x480, q=2-31, 200 kb/s, 25 fps, 25 tbn, 25 tbc
    Metadata:
      encoder         : Lavc58.35.100 mjpeg
    Side data:
      cpb: bitrate max/min/avg: 0/0/200000 buffer size: 0 vbv_delay: -1
frame=    1 fps=0.4 q=6.8 Lsize=N/A time=00:00:01.04 bitrate=N/A speed=0.467x    
video:63kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: unknown


  


  Note, achieved FPS is 0.4. When I increase the requested frame to be the 125th frame rather than the 25th, the FPS goes down to 0.1.

  


• avformat/aviobuf : Avoid allocation when using dynamic buffer

  4 août 2021, par Andreas Rheinhardt

  avformat/aviobuf : Avoid allocation when using dynamic buffer
  This can be achieved by allocating the AVIOContext and
  
  the dynamic buffer's opaque and internal write buffer together.
  Signed-off-by : Andreas Rheinhardt <andreas.rheinhardt@outlook.com>
  

  • [DH] libavformat/aviobuf.c

• asyncio.create_subprocess_shell error : Future exception was never retrieved - BrokenPipeError

  10 juin 2021, par Abdelmalek

  Whenever I use asyncio.create_subprocess_shell() with sp.communicate() I get this error at the end of my program.

  


  If I run multiple suprocesses using asyncio, the error would be print at the end for each one of them.

  


  Aulthough it doesn't affect my program, I want to find the source and fix the issue. Thanks for the help !

  


  Traceback :

  


  Future exception was never retrieved&#xA;future: <future finished="finished" exception="BrokenPipeError(32," pipe="pipe" has="has" been="been">&#xA;Traceback (most recent call last):&#xA;  File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\subprocess.py", line 153, in _feed_stdin&#xA;    await self.stdin.drain()&#xA;  File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\streams.py", line 387, in drain&#xA;    await self._protocol._drain_helper()&#xA;  File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\streams.py", line 197, in _drain_helper&#xA;    await waiter&#xA;  File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\proactor_events.py", line 379, in _loop_writing&#xA;    f.result()&#xA;  File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\windows_events.py", line 812, in _poll&#xA;    value = callback(transferred, key, ov)&#xA;  File "C:\Users\user\AppData\Local\Programs\Python\Python39\lib\asyncio\windows_events.py", line 538, in finish_send&#xA;    return ov.getresult()&#xA;BrokenPipeError: [WinError 109] The pipe has been ended&#xA;</future>

  


  Code :

  


  async def get(cs, url):
    async with cs.get(url) as r:
        b = b''
        while True:
            chunk = await r.content.read(4000000)
            b += chunk
            if not chunk:
                break
        
        if int(r.headers['content-length']) < 8000000:
            result = BytesIO(b)
            return [result, 'full']
        else:
            command = f"ffmpeg -y -i - -c:v copy -fs 8000000 -f matroska -"
            sp = await asyncio.create_subprocess_shell(command, stdin=asyncio.subprocess.PIPE,
                stdout=asyncio.subprocess.PIPE, stderr=asyncio.subprocess.PIPE)
            stdout, stderr = await sp.communicate(b)
            sp.wait()

            print(stderr.decode())
            print(len(stdout))
            output = str(stderr)
            index_d = output.find('Duration: ')
            index_t = output.rfind('time=')
            duration = await get_sec(output[index_d + 10:].split(",")[0])
            time_ = await get_sec(output[index_t + 5:].split(" ")[0])
            percentage = f"{round((time_ / duration) * 100)}%"

            result = BytesIO(stdout)
            return [result, 'preview', percentage]

async def main(urls):
    async with aiohttp.ClientSession() as cs:
            
        tasks = []
        for url in urls:
            task = asyncio.create_task(get(cs, url))
            tasks.append(task)
        
        results = []
        for task in tasks:
            result = await task
            results.append(result)
        
        return results

loop = asyncio.get_event_loop()
results = loop.run_until_complete(main(urls))