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• How correctly show video with transparency in Qt with OpenCV + FFMpeg

  11 avril 2022, par TheEnigmist

  I'm trying to show a video with transparency in a Qt6 application using OpenCV + FFMPEG.
Actually those are tool versions :

  


  

  • Win 11

  


  • Qt 6.3.0

  


  • OpenCV 4.5.5 (built with CMake)

  


  • FFMPEG 2022-04-03-git-1291568c98-full_build-www.gyan.dev

  


  


  I've used a base .mov video with transparency as test (link provided below).
First of all I've converted .mov video to .webm video (VP9) and I see in output text that alpha channel remains

  


  


  ffmpeg -i '.\Retro Bars.mov' -c:v libvpx-vp9 -crf 30 -b:v 0 output.webm

  


  


  Input #0, mov,mp4,m4a,3gp,3g2,mj2,
    ...
    Stream #0:0[0x1](eng): Video: qtrle (rle  / 0x20656C72), argb(progressive),
    ...

Output #0, webm, 
   ...
   Stream #0:0(eng): Video: vp9, yuva420p(tv, progressive),
   ...


  


  But when I show info of output file with ffmpeg it loses alpha channel :

  


  


  ffmpeg -i .\output.webm

  


  


  Input #0, matroska,webm,
    ...
    Stream #0:0(eng): Video: vp9 (Profile 0), yuv420p(tv, progressive),
    ...


  


  If I open output.webm with OBS it is shown correctly without a background, as shown in picture :


  


  If I try to open it with OpenCV + FFMPEG it shows a black background under bars, as shown in picture :


  


  This is how I load video in Qt :

  


  cv::VideoCapture capture;
capture.open(filename, cv::CAP_FFMPEG);
capture.set(cv::CAP_PROP_CONVERT_RGB, false); // try forcing load alpha channel
... //in a thread
while (capture.read(frame)) {
    qDebug() << "c" << frame.channels() << "t" <<  frame.type() << "d" <<  frame.depth(); // output: c 3 t 16 d 0
    cv::cvtColor(frame, frame, cv::COLOR_BGR2RGBA); //useless since no alpha channel is detected
    img = QImage(frame.data, frame.cols, frame.rows, QImage::Format_RGBA8888);
    emit processedImage(img); // to show image in a QLabel with QPixmap::fromImage(img)
}


  


  I think the problem is when I load the video with OpenCV, it doens't detect alpha channel, since I can load correctly in other player (obs, html5, etc.)

  


  What I'm wrong with all process to show this video in Qt with transparency ?

  


  EDIT : Added dropbox link with test video + ffmpeg outputs :
sample items

  


• I tried to play the audio on Alexa skill from my S3 Bucket, from the test tab, **it show but in fact, I can't hear any sound

  19 avril 2022, par Siti Mayna

  So I tried to play the audio on Alexa skill from my S3 Bucket, from the test tab, it show but in fact, I can't hear any sound. Another fact is, that I tried to use the sample audio from https://developer.amazon.com/en-US/docs/alexa/custom-skills/ask-soundlibrary.html and it is worked, but why it won't work when it comes from my own S3 Bucket ?

  


  Notes :

  


  I've tried to test the skill using my mobile phone also.

  


  I've tried to encode the audio using FFmpeg.

  


  I've tried to use Jovo to convert the audio. https://v3.jovo.tech/audio-converter

  


  I don't know how to fix this error.

  


  There is no error message on cloud watch.

  


  Assumptions :
There is some problem related to the audio resources or there is more set to play audio from S3 Bucket since the sample audio is working.

  


  Steps to reproduce :

  


  


  Build the interaction model

  


  


  


  Encode the audio to make it Alexa skill friendly (fulfill the requirements, like sample rate, etc), I used and tried all of these :

  


  


  A :

  


  ffmpeg -i  -ac 2 -codec:a libmp3lame -b:a 48k -ar 16000 -write_xing 0 


  


  B :

  


  ffmpeg -i  -ac 2 -codec:a libmp3lame -b:a 48k -ar 24000 -write_xing 0 


  


  C :

  


  ffmpeg -y -i input.mp3 -ar 16000 -ab 48k -codec:a libmp3lame -ac 1 output.mp3


  


  


  Upload the audio resources on S3Bucket
Audio sample on s3 storage but none of them are produce any sounds

  


  


  


  Use the link and insert it to APLA.json

  


  


  
    {
      "type": "APLA",
      "version": "0.91",
      "description": "Simple document that generates speech",
      "mainTemplate": {
        "parameters": [
          "payload"
        ],
        "type": "Sequencer",
        "items": [
          {
            "type": "Audio",
            "source": "https://72578561-d9d8-47b4-811c-cafbcbc5ddb9-us-east-1.s3.amazonaws.com/Media/one-small-step-alexa-24.mp3"
          }
        ]
      }
    }



  


  notes : I change the link sources based on audio that I tried.

  


  


  the intent on lambda_function.py :

  


  


  def _load_apl_document(file_path):
    # type: (str) -> Dict[str, Any]
    """Load the apl json document at the path into a dict object."""
    with open(file_path) as f:
        return json.load(f)

class LaunchRequestHandler(AbstractRequestHandler):
    """Handler for Skill Launch."""
    def can_handle(self, handler_input):
        # type: (HandlerInput) -> bool

        return ask_utils.is_request_type("LaunchRequest")(handler_input)

    def handle(self, handler_input):
        # type: (HandlerInput) -> Response
        logger.info("In LaunchRequestHandler")

        # type: (HandlerInput) -> Response
        speak_output = "Hello World!"
        # .ask("add a reprompt if you want to keep the session open for the user to respond")

        return (
            handler_input.response_builder
                #.speak(speak_output)
                .add_directive(
                        RenderDocumentDirective(
                            token="pagerToken",
                            document=_load_apl_document("APLA.json"),
                            datasources={}
                        )
                    )
                .response
        )


  


  


  Deploy

  


  


  


  Test it

  


  


  


  The result of the test on my end :

The response for testing

  


  


  the JSON response :

  


  {
    "body": {
        "version": "1.0",
        "response": {
            "directives": [
                {
                    "type": "Alexa.Presentation.APLA.RenderDocument",
                    "token": "pagerToken",
                    "document": {
                        "type": "APLA",
                        "version": "0.91",
                        "description": "Simple document that generates speech",
                        "mainTemplate": {
                            "parameters": [
                                "payload"
                            ],
                            "type": "Sequencer",
                            "items": [
                                {
                                    "type": "Audio",
                                    "source": "https://72578561-d9d8-47b4-811c-cafbcbc5ddb9-us-east-1.s3.amazonaws.com/Media/one-small-step-alexa-24.mp3"
                                }
                            ]
                        }
                    },
                    "datasources": {}
                }
            ],
            "type": "_DEFAULT_RESPONSE"
        },
        "sessionAttributes": {},
        "userAgent": "ask-python/1.16.1 Python/3.7.12"
    }
}


  


  


  On my cloud Watch :
Cloud Watch

  


  


• Show progress bar of a ffmpeg video convertion

  13 juin 2022, par stackexchange.com-upvm25mz

  I'm trying to print a progress bar while executing ffmpeg but I'm having trouble getting the total number of frames and the current frame being processed. The error I get is AttributeError: 'NoneType' object has no attribute 'groups'. I've copied the function from this program and for some reason it works there but not here, even though I haven't changed that part.

  


  main.py

  


  pattern_duration = re.compile(
    'duration[ \t\r]?:[ \t\r]?(.+?),[ \t\r]?start', re.IGNORECASE)
pattern_progress = re.compile('time=(.+?)[ \t\r]?bitrate', re.IGNORECASE)

def execute_ffmpeg(self, manager, cmd):
    proc = expect.spawn(cmd, encoding='utf-8')
    self.update_progress_bar(proc, manager)
    self.raise_ffmpeg_error(proc)

def update_progress_bar(self, proc, manager):
    total = self.get_total_frames(proc)
    cont = 0
    pbar = self.initialize_progress_bar(manager)
    try:
        proc.expect(pattern_duration)
        while True:
            progress = self.get_current_frame(proc)
            percent = progress / total * 100
            pbar.update(percent - cont)
            cont = percent
    except expect.EOF:
        pass
    finally:
        if pbar is not None:
            pbar.close()

def raise_ffmpeg_error(self, proc):
    proc.expect(expect.EOF)
    res = proc.before
    res += proc.read()
    exitstatus = proc.wait()
    if exitstatus:
        raise ffmpeg.Error('ffmpeg', '', res)

def initialize_progress_bar(self, manager):
    pbar = None
    pbar = manager.counter(
        total=100,
        desc=self.path.rsplit(os.path.sep, 1)[-1],
        unit='%',
        bar_format=BAR_FMT,
        counter_format=COUNTER_FMT,
        leave=False
    )
    return pbar

def get_total_frames(self, proc):
    return sum(map(lambda x: float(
        x[1])*60**x[0], enumerate(reversed(proc.match.groups()[0].strip().split(':')))))

def get_current_frame(self, proc):
    proc.expect(pattern_progress)
    return sum(map(lambda x: float(
                x[1])*60**x[0], enumerate(reversed(proc.match.groups()[0].strip().split(':')))))