Extracting values from a char variable

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Adam
Adam 2022-12-14
评论： Stephen23 2022-12-14
Ran in:
I am running FFmpeg through the system() function and the output is being stored within a char variable cmdout. I have added minimal reproducible code.
cmdout = "Guessed Channel Layout for Input Stream #0.0 : monoInput #0, wav, from 'testwav.wav': Duration: 00:00:02.92, bitrate: 256 kb/s Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/sStream mapping: Stream #0:0 -> #0:0 (pcm_s16le (native) -> opus (libopus))Press [q] to stop, [?] for helpOutput #0, opus, to 'test.opus': Metadata: encoder : Lavf59.27.100 Stream #0:0: Audio: opus, 16000 Hz, mono, s16, 8 kb/s Metadata: encoder : Lavc59.37.100 libopussize= 0kB time=00:00:00.12 bitrate= 8.8kbits/s speed=N/A size= 13kB time=00:00:02.92 bitrate= 35.8kbits/s speed= 241x video:0kB audio:11kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 12.397972%bench: utime=0.000s stime=0.016s rtime=0.012sbench: maxrss=14764kB";
This is how it displayed on the command window (without the %).
%Guessed Channel Layout for Input Stream #0.0 : mono
%Input #0, wav, from 'testwav.wav':
% Duration: 00:00:02.92, bitrate: 256 kb/s
% Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s
%Stream mapping:
% Stream #0:0 -> #0:0 (pcm_s16le (native) -> opus (libopus))
%Press [q] to stop, [?] for help
%Output #0, opus, to 'test.opus':
% Metadata:
% encoder : Lavf59.27.100
% Stream #0:0: Audio: opus, 16000 Hz, mono, s16, 8 kb/s
% Metadata:
% encoder : Lavc59.37.100 libopus
%size= 0kB time=00:00:00.12 bitrate= 8.8kbits/s speed=N/A
%size= 13kB time=00:00:02.92 bitrate= 35.8kbits/s speed= 241x
%video:0kB audio:11kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 12.397972%
%bench: utime=0.000s stime=0.016s rtime=0.012s
%bench: maxrss=14764kB
I am trying to extract out the values of the following
  • 'Duration: 00:00:02.92'
  • 'bitrate: 256'
  • 'Stream #0:0: Audio: opus, 16000 Hz, mono, s16, 8 kb/s'
  • 'encoder : Lavc59.37.100 libopus'
  • 'utime=0.000'
  • 'stime=0.016'
  • 'rtime=0.012'
So far I have I am currently using the regexp() function to extract out the values into a struct.
Values = regexp(cmdout,'(?<utime>utime=.{5})','names'); % Only one working so far
for k = 1:length(Values)
disp(Values(k))
end
utime: "utime=0.000"
I have been unable to add multiple regex statements without it failing to find anything. I was also not sure if it was possible to have the struct just store the actual value e.g. utime: '0.000' rather than how it currently also contains the text.
  5 个评论
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Adam
Adam 2022-12-14
The one that contains "Audio: opus" after it.
Stephen23
Stephen23 2022-12-14
And how to distinguish between the lines containing "encoder :" ?

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Stephen23
Stephen23 2022-12-14
编辑：Stephen23 2022-12-14
Ran in:
str = fileread('text.txt')
str =
'Guessed Channel Layout for Input Stream #0.0 : mono Input #0, wav, from 'testwav.wav': Duration: 00:00:02.92, bitrate: 256 kb/s Stream #0:0: Audio: pcm_s16le ([1][0][0][0] / 0x0001), 16000 Hz, mono, s16, 256 kb/s Stream mapping: Stream #0:0 -> #0:0 (pcm_s16le (native) -> opus (libopus)) Press [q] to stop, [?] for help Output #0, opus, to 'test.opus': Metadata: encoder : Lavf59.27.100 Stream #0:0: Audio: opus, 16000 Hz, mono, s16, 8 kb/s Metadata: encoder : Lavc59.37.100 libopus size= 0kB time=00:00:00.12 bitrate= 8.8kbits/s speed=N/A size= 13kB time=00:00:02.92 bitrate= 35.8kbits/s speed= 241x video:0kB audio:11kB subtitle:0kB other streams:0kB global headers:0kB muxing overhead: 12.397972% bench: utime=0.000s stime=0.016s rtime=0.012s bench: maxrss=14764kB'
In three separate REGEXP calls (combining may be possible, but only with significant effort and complexity):
rx1 = "(Duration|bitrate|encoder)\s*:\s+([^,\n\r]+)";
tk1 = regexp(str,rx1,'tokens');
tk1 = vertcat(tk1{:})
tk1 = 4×2 cell array
{'Duration'} {'00:00:02.92' } {'bitrate' } {'256 kb/s' } {'encoder' } {'Lavf59.27.100' } {'encoder' } {'Lavc59.37.100 libopus'}
rx2 = "(Stream\s+\S+\s+Audio:)\s+(opus[^\n\r]+)";
tk2 = regexp(str,rx2,'tokens','once')
tk2 = 1×2 cell array
{'Stream #0:0: Audio:'} {'opus, 16000 Hz, mono, s16, 8 kb/s'}
rx3 = "([a-z]time)=(\d\.?\d*)";
tk3 = regexp(str,rx3,'tokens');
tk3 = vertcat(tk3{:})
tk3 = 3×2 cell array
{'utime'} {'0.000'} {'stime'} {'0.016'} {'rtime'} {'0.012'}
  2 个评论
Adam
Adam 2022-12-14
Thanks for the help. Is there any interactive or alternative sources for understanding the regexp commands. Something like Regex 101 but for MATLAB
Stephen23
Stephen23 2022-12-14
"Something like Regex 101 but for MATLAB"
There are several interactive tools on MATLAB FEX:
https://www.mathworks.com/matlabcentral/fileexchange?q=regular+expressions
For example, my one is intended to be the simplest interactive tool on FEX:
https://www.mathworks.com/matlabcentral/fileexchange/48930-interactive-regular-expression-tool
Not as fancy as Regex 101, but it might help you enough.
"...alternative sources for understanding the regexp commands"
Repeated reading of the documentation. And when I write "repeated", I don't mean twice.
https://www.mathworks.com/help/matlab/matlab_prog/regular-expressions.html

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