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• twinvq : move all bitstream reading into single place

  4 août 2013, par Kostya Shishkov

  twinvq : move all bitstream reading into single place
  This is required for the future addition of VoxWare MetaSound decoder, for its
  
  functions are mostly the same but bitstream reader is completely different
  
  and bitstream format is slightly different too.
  Signed-off-by : Diego Biurrun <diego@biurrun.de>
  

  • [DBH] libavcodec/twinvq.c

• Read portion of lines from child process in Rust (chunk of data)

  2 octobre 2022, par Alexey Volodko

  When I try to spawn a child ffmpeg process I use additonal flag -progress, next I use pipe to pass this progress output to the stderr.
So the whole command looks like :

  


  ffmpeg -i ... -progress pipe:2 ...


  


  Without -progress flag ffmepg outputs following line in stderr, probably once per second :

  


  frame=46 46 fps=0.0 q=0.0 size=       0kB time=00:00:01.72 bitrate=   0.2kbits/s speed=2.69x


  


  With -progress flag ffmepg outputs (multiple lines) in stderr, probably once per second :

  


  frame=1   1 fps=0.0 q=0.0 size=       0kB time=00:00:00.19 bitrate=   2.0kbits/s speed=2.94x    
fps=0.00
stream_0_0_q=0.0
bitrate=   2.0kbits/s
total_size=48
out_time_us=192000
out_time_ms=192000
out_time=00:00:00.192000
dup_frames=0
drop_frames=0
speed=2.94x
progress=continue


  


  The main puppose of using -progress flag is to calc percentage of completion by parsing out_time_ms line and comparing to the whole duration.

  


  Reading this chunk (portion of lines) is pretty simple in NodeJS :

  


  const { spawn } = require('child_process');
const child = spawn('ffmpeg', [..., '-progress', 'pipe:2', ...]);

child.stderr.on('data', (data) => {
  // data will contain multiple lines, exactly one chunk
});


  


  Reading this chunk (portion of lines) is pretty simple in Deno also :

  


  const child = Deno.spawnChild("ffmpeg", {
  args: [..., '-progress', 'pipe:2', ...],
});
const stderrReader = child.stderr.getReader();
let readResult = await stderrReader.read();
while (readResult.done !== true) {
  readResult = await stderrReader.read();
  // readResult will contain multiple lines, exactly one chunk
}


  


  I can't achieve the same in rust :

  


  let mut command = Command::new("ffmpeg");
command.args(["...", "-progress", "pipe:2", "..."]);
let mut child = command
  .stdout(Stdio::piped())
  .stderr(Stdio::piped())
  .spawn()
  .unwrap();

let child_stderr = child.stderr.as_mut().expect("Unable to pipe stderr");
let mut reader = BufReader::new(child_stderr);
let mut buff = String::new();
while reader.read_line(&mut buff).expect("Unable to read chunk") > 0 {
  // buff will contain only on line
  buff.clear();
}


  


  I am new in Rust. I can not detect what character signals end of chunk.

  


  

  • Runnig read_line() - will read only one line.

  


  • Runnig read_to_end() - will read the whole output until the end of process (EOF).

  


  


  How can I read in Rust portion of lines that ffmpeg outputs probably once per second ?
How Node/Deno detects this "end of chunk" ?
Does rust have such event/signal also ?

  


• ffmpeg : test if format is seekable

  20 mai 2021, par Diederick C. Niehorster

  How do i test if a format is seekable ?

  


  I have written code against the latest fmmpeg's (4.4) libavformat, libavcodec, etc. My code reads and decodes video files. Now i also want to support reading from avdevices, such as dshow (DirectShow) on Windows. That is possible through the same interface as i have already implemented, it just requires using the dshow format. Super nice ! But in my video file reader, i have some seek logic implemented, which is engaged in various instances. The problem is that the dshow format is not seekable (avformat_seek_file() returns -22, invalid argument). How do i detect that a format is not seekable ? I know that the AVFormatContext's pb member (AVIOContext) has a seekable field, but the dshow format leaves pb null (as it should be since the AVFMT_NOFILE flag is set for the format). How do i test if a format is seekable (so that if it is not, i can disable the seek logic) ? The implementation of avformat_seek_file() and the various functions it calls seems to have various callbacks, so i am not sure if simply this would do the trick : bool isSeekable = !!context->pb && context->pb->seekable!=0.