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 Extract Video from Dicom
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Ronald Ruijs

Netherlands
20 Posts

Posted - Feb 15 2021 :  04:42:02  Show Profile  Reply
For those who work with Dicom Files, you may encounter a Dicom file containing video data (mpeg-2, mpeg-4, hevc). In order to extract the video data and save as Media File, the following info may be useful:

- Video is encapsulated data in pixel tag (7fe0,0010)
- All data is in 1 frame
- Basic offset table is empty (8 bytes)
- In frame, first 4 bytes contain frame content length as Cardinal (this is the size of the video data)

So, to extract video data:

- Get TDicomReadContext.ImagePos
- Content length is Cardinal at ImagePos + 12 (skip 8 bytes of Basic Offset Table and 4 bytes for sequence tag (FFFE,E000).
- Video Data Starts at ImagePos + 16 (after content length)

Code below to get you started. Refer also to https://stackoverflow.com/questions/20880303/dicom-undefined-tag-length-pixels#:~:text=%22If%20the%20Value%20Field%20has,end%20of%20the%20Value%20Field.%20%22.

Regards, Ronald

procedure SaveDicomVideoToFile(ADicomFile, AMediaFile: string);
var
  Ms: TMemoryStream;
  p,n: Cardinal;
begin
  Ms := TMemoryStream.Create;

  with Ms do
  try
    LoadFromFile(ADicomFile);

    p := GetVideoDataOffset(Ms);  <- ImagePos + 16
    n := GetVideoDataLength(Ms);  <- ImagePos + 12

    Position := p;

    with TMemoryStream.Create do
    try
      CopyFrom(Ms, n);
      SaveToFile(AMediaFile);
    finally
      Free;
    end;
  finally
    Free;
  end;
end;

//------------------------------------------------------------------------------------------------//
//
//------------------------------------------------------------------------------------------------//
function GetVideoDataOffset(AStream: TStream): Cardinal;
var
  Pr: TProgressRec;
  b: Boolean;
begin
  Pr := NullProgressRec(b, False);

  with TImageEnIO.Create(nil) do
  try
    AStream.Position := 0;

    with TDicomReadContext.Create(AStream, Pr) do
    try
      ReadHeader;
      ReadTags(Params);

      Result := ImagePos + 16;
    finally
      Free;
    end;
  finally
    Free;
  end;
end;

xequte

5869 Posts

Posted - Feb 16 2021 :  15:59:05  Show Profile  Reply
Thanks Ronald!

Nigel
Xequte Software
www.imageen.com
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