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• FFmpeg low framerate when adding audio

  22 juillet 2021, par Massi

  we are sending a video from a Linux PC with GPU (Alienware M15 R2 so very strong in hardware) connected to a Logitech Brio 4K resolution camera.
We are using ffmpeg and in particular the following command :

  


  ffmpeg -re -hwaccel cuvid -hwaccel_output_format cuda -f v4l2 -input_format mjpeg -framerate 30 -video_size 3840x2160 -i /dev/video4 -f pulse -i default -c:v h264_nvenc -tune ull -preset llhq -zerolatency true -pix_fmt rgb0 -c:a aac -aac_coder fast -ar 44100 -b:a 256k -b:v 25000k -threads 0 -f flv "rtmp ://192.168.1.1/WebRTCAppEE/XXX"

  


  As you can see this is the part related to audio "-c:a aac -aac_coder fast -ar 44100 -b:a 256k"
If we send the script WITHOUT the audio part, we see it very fluid even in 4K resolution, with 30 FPS, but of course with no audio.
If we send the script WITH the audio part, the FPS goes down to 19-20 and the video is no more fluid. In this case we tried also to downgrade the video quality, but the result is always the same, the video is not fluid, even if the PC has not the CPU and GPU very loaded.
Would you suggest another script or some correction in order to avoid this problem and stream a video getting both video and audio from a device ?

  


• Use ffprobe to view audio tracks by language [on hold]

  19 novembre 2016, par crosenblum

  I wish to use ffprobe to list all audio streams, and show what language is used.

  Simply this is part of me trying to find ways to automatically remove non-english tracks from video files.

  I am new to ffprobe, but have had some experience using ffmpeg.

  Because I know that there is no guarantee of what order the language tracks may be.

  That is why I think it is vital to list each track, by number, then language, then when I know this part works, figure out how to remove the non-english ones.

  Thanks for your time.

• Using FFmpeg to detect alpha channel in PR4444 file [closed]

  8 décembre 2023, par Justin Myers

  I wanted to comment on a thread that already exists on this topic in general, but I just signed up to SO and have not earned my contribution credits yet ! If anyone has advice on how to better handle that in the future, I am all ears !!

  


  None-the-less, here is that thread :

  


  A good way to detect alpha channel in a video using ffmpeg/ffprobe

  


  I tried both the answers listed in that post to detect the presence of an alpha channel in a PR4444 video file.

  


  For Gyan's answer, I get the following pixel format from any PR4444 file (regardless if encoded with alpha or no alpha), when running part 1 :

  


  yuva444p12le

  


  As you will see in Gyan's notes, even if a FFprobe returns an "a" in the return string (for the call for pixel format), that does not equate to the presence of an alpha channel. Hence their note for the subsequent (part 2) call...

  


  I then plugged that into the part 2 of Gyan's answer, but that produced an empty from FFmpeg, and a message providing valid arguments to pair with grep. It seems as though -oP is not a valid arg for grep ? Because it wasn't listed in the returned list of options. This is the template I used (pulled verbatim from Gyan's posted solution) :

  


  ffprobe -v 0 -show_entries pixel_format=name:flags=alpha -of compact=p=0 | grep "$PIX_FMT|" | grep -oP "(?<=alpha=)\d"

  &#xA;

  Where $PIX_FMT is to be replaced with yuva444p121e (per Gyan's instructions).

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  I then tried Benji's solution for part 2, but that just returns the following :

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  pix_fmt=yuva444p12le

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  Of course, this isn't any more useful than part 1...

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  I suspect Gyan is on the right track as he mentions part 2 should produce a boolean result for the presence of an alpha channel. However, either I am misunderstanding the syntax of his template, or something has changed in FFprobe since. There is so limited information out there for this specific task. Hoping someone with more experience and knowledge can help shed some light for me ??

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