I'm reading and writing audio from a named pipe. I'm running into an issue where my read process lags, causing the pipe's buffer to fill up and drop frames. I'd like to insert a buffer of arbitrarily large size into the pipe.

I'm trying to use 'dd' to do this, but 'obs' and 'ibs' seem to refer to read/write block size, not buffer size?

Is there a way to use 'dd' for this purpose?

  • What about stdbuf? – user147505 Feb 15 '17 at 0:47

It could be used as such, but it sucks.

For example, dd bs=1M would be a 1 MiB buffer, however it might not solve your audio problem. If dd gets a short read, it will pass that along directly, so it won't use the buffer as such. You can add iflag=fullblock to force dd filling up its buffer entirely, but then it would read 1 MiB of data, write 1 MiB of data, read 1 MiB of data, ... dd won't accept new input before the output step is done, so your "buffer" would be 100% full, 100% empty, 100% full... and for however long it takes the buffer to fill up / empty out, the other side will be stuck.

This is not a characteristic you want/expect when thinking of pipe buffers. If you look at actual pipe buffers such as bfr or pv, they all accept new input while output is going on, they strive to maintain a good fill rate throughout so neither side has to wait more than absolutely necessary.

With a real pipe buffer, input will always be accepted (while the buffer is not full) and output will always be provided (while the buffer is not empty) and they might have advanced options such as guaranteeing a prefill, min-fill, ...

dd doesn't do any of that, in fact dd relies on buffering being done on the outside, when working with block devices, read/write concurrency is largely provided by the kernel (readahead/cache/...).

Basically you'd only consider dd as a pipe buffer in minimalistic environments that have no other programs suited to the task available.

If you must use dd but the characteristics of dd are not suited to your task, you could daisy chain multiple dd to get a "smoother" result of a buffer. But even then it might not be suitable for some use cases.

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  • Thanks for the detailed reply. I had no idea dd is incapable of simultaneous reads and writes to the buffer. This sounds unsuitable. – user2989813 Feb 15 '17 at 1:02

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