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• 4K Screen Recording on 1080p Monitors [closed]

  10 avril, par Souhail Benlhachemi

  I have created a basic windows screen recording app (ffmpeg + GUI), but I noticed that the quality of the recording depends on the monitor used to record, the video recording quality when recorded using a full HD is different from he video recording quality when recorded using a 4k monitor (which is obvious).

  


  There is not much difference between the two when playing the recorded video with a scale of 100%, but when I zoom to 150% or more, we clearly can see the difference between the two recorded videos (1920x1080 VS the 4k).

  


  I did some research on how to do screen recording with a 4k quality on a full hd monitor, and here is what I found :

  


  I played with the windows duplicate API (AcquireNextFrame function which gives you the next frame on the swap chain), I successfully managed to convert the buffer to a PNG image and save it locally to my machine, but as you expect the quality was the same as a normal screenshot ! Because AcquireNextFrame return a frame after it is rasterized.

  


  Then I came across what’s called “Graphics pipeline”, I spent some time to understand the basics, and finally I came to a conclusion that I need to intercept somehow the pre-rasterize data (the data that comes before the Rasterizer Stage - Geometry shaders, etc...) and then duplicate this data and do an off-screen render on a new 4k render target, but the windows API don’t allow that, there is no way to do that ! The only option they have on docs is what’s called Stream Output Stage, but this is useful only if you want to render your own shaders, not the ones that my display is using. (I tried to use MinHook to intercept data but no luck).

  


  After that, I tried a different approach, I managed to create a virtual display as extended monitor with 4k resolution, and record it using ffmpeg, but as you know what I’m seeing on my main display on my monitor is different from the virtual display (only an empty desktop), what I need to do is drag and drop app windows using my mouse to that screen manually, but this will put us in a problem when recording, we are not seeing what we are recording xD.

  


  I found some YouTube videos that talk about DSR (Dynamic Super Resolution), I tried that on my nvidia control panel (manually with GUI) and it works. I managed to fake the system that I have a 4k monitor and the quality of the recording was crystal clear. But I didn’t find anyway to do that programmatically using NVAPI + there is no API for that on AMD.

  


  Has anyone worked on a similar project ? Or know a similar project that I can use as reference ?

  


  suggestions ?

  


• Batch extract and batch inject Dolby Vision metadata

  6 décembre 2023, par Amanda

  newbie here.

  


  After having successfully used the batch commands to extract and inject HDR10+ json metadata through hdr10plus_tool found on GitHub, I'm now trying to figure out how to correctly set up the same actions for the Dolby Vision, via dovi_tool (still the one you can find on GitHub, by QuietVoid).

  


  I'm first of all using this command to export DoVi data via json files from all of my mkv's :

  


  for file in *.mkv; do     [ -e "$file" ] && ffmpeg -i "$file" -map 0:v:0 -c copy -f hevc - | /Users/myself/myfolder/dovi_tool extract-rpu -o "${file%.mkv}_metadata.json" - done

  


  ...then, am using this other one for batch injecting those metadata :

  


  for hevc_file in "/Volumes/myhdd/myfolder"/*.h265; doif [ -e "$hevc_file" ]; thendirectory=$(dirname "$hevc_file")file_name=$(basename "$hevc_file" .h265)json_file="$directory/$file_name.json"

  


  `if [ -f "$json_file" ] ; then
new_mkv_file="$directory/$file_name_dovi.mkv"

  


      /Users/myself/myfolder/dovi_tool inject-rpu -i "$hevc_file" --rpu-in "$json_file" -o "$new_mkv_file"
else
    echo "File JSON not found for $hevc_file"
fi


  


  fi`

  


  done

  


  ...this last command, apparently makes what it is supposed to do, I can see the percentage injection status until it's done, for every file. But then, when I check the mkv created, I see no Dolby Vision in it.
I am wondering where am I mistaken.

  


  Maybe in the first code for extraction, I am using a wrong command that generates broken DoVi data ? Should I have extracted via xml rather than json ?
Please give me some hints (I am using a mac, so I don't have the same gui people uses on windows), and also, I would like to use this method via terminal in order to be able to work in batch.

  


  I would like to batch export DoVi metadata from a folder with the bdremux mkv's, and then inject them from within a folder containing the encoded mkv's.

  


• multichannel (dolby digital, DTS, ecc.) delay difference on original master

  17 janvier 2017, par esposito

  I have different flac files with 6/8 channels (this is the audio of movie) and I need to mix with ffmpeg part of rear channels with front channels and sometimes viceversa.

  There is no problem do it the operation work with an automate software.

  But I’am sure there is a phase difference beetween front channels and rear channels and I like to add a delay to compensate this difference (when I listen it is clear there is a phase offset and this degrade the result).

  I don’t have an idea about how many milliseconds I need to add to compensate and what channel and if the difference is negative or positive.

  Someone can help me please to understand approximately what are the range of delay for each channel (a table is very useful) ?

  Thank you !!