Delphi: Capture OSX console output - delphi

Question

I am on OSX and I found the following Delphi (Firemonkey) code to write the console output to a Memo. This works fine when I am using normal commands like "ls", but it doesn't capture the output from external terminal apps.
For example, if I run the command line application "youtube-dl", the output shows up only in the PAServer log, but not in the Memo.
Is there a way to do this? Or can someone modify the code to make this work?
const
libc = '/usr/lib/libc.dylib';
type
PIOFile = Pointer;
//Create a new stream connected to a pipe running the given command.
function popen(const Command: PAnsiChar; Modes: PAnsiChar): PIOFile; cdecl;
external libc name '_popen';
//Close a stream opened by popen and return the status of its child.
function pclose(Stream: PIOFile): Integer; cdecl; external libc name '_pclose';
//Return the EOF indicator for STREAM.
function feof(Stream: PIOFile): Integer; cdecl; external libc name '_feof';
//Read chunks of generic data from STREAM.
function fread(Ptr: Pointer; Size: LongWord; N: LongWord;
Stream: PIOFile): LongWord; cdecl; external libc name '_fread';
//Wait for a child to die. When one does, put its status in *STAT_LOC
//and return its process ID. For errors, return (pid_t) -1.
function wait(__stat_loc: PInteger): Integer; cdecl;
external libc name '_wait';
procedure TForm1.ExecCmdine(const CmdLine: string);
var
Output: PIOFile;
Buffer: PAnsiChar;
TempString: Ansistring;
Line: AnsiString;
BytesRead: Integer;
const
BufferSize: Integer = 1000;
begin
TempString := '';
Output := popen(PAnsiChar(Ansistring(CmdLine)), 'r');
GetMem(Buffer, BufferSize);
if Assigned(Output) then
try
while feof(Output) = 0 do
begin
BytesRead := fread(Buffer, 1, BufferSize, Output);
SetLength(TempString, Length(TempString) + BytesRead);
Move(Buffer^, TempString[length(TempString) - (BytesRead - 1)], BytesRead);
while Pos(#10, TempString) > 0 do
begin
Line := Copy(TempString, 1, Pos(#10, TempString) - 1);
Memo1.Lines.Add(UTF8ToString(Line));
TempString := Copy(TempString, Pos(#10, TempString) + 1, Length(TempString));
end;
end;
finally
pclose(output);
wait(nil);
FreeMem(Buffer, BufferSize);
end;
end;

Answer 1

Rob Kennedy had the correct answer, but sadly he didn't post it as answer, so I will do it.
The problem was that the console output of youtube-dl gets printed to stderr and not stdout, so I had to add 2>&1 to the console command when running it.