| | Open Sound System |
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int route;
ioctl(fd, SNDCTL_DSP_SET_RECSRC, &route);
The above code fragment lacks all error checks for clarity. Real world applications must always check for the errors and handle them as described below. Also most OSS ioctl calls will return information in the argument variable and it's usually necessary to check it too.
This ioctl call changes the current recording source. The returned value is a number between 0 and N. The meaning of the number depends on the device and it's current setup. There are no predefined values. The application needs to use SNDCTL_DSP_GET_RECSRC_NAMES to figure out the currently available recording sources. See the Audio input and output volumes and routings section for more info about the routing mechanism.
The value that was accepted by the device will be returned back in the variable pointed by the argument. However it's possible that some other application or user changes the setting to some other value after a while. Applications that want to keep their GUI up to date must check the active value regularily to se if it has changed.
In some cases changing the playback target or recording source may affect the possible sampling rates or formats. For this reason it's recommended that the source/target selections are changed only before checking or setting the rate and other audio stream parameters (or recording and playback volumes).
It's possible that the selected source device is in use by some application which makes changing the selection impossible. In this situation this ioctl call will return -1 with errno set to EBUSY. This is more or less temporary situation which will go away when the conflicting application is closed.
Traditionally many audio applications have used the mixer ioctl calls to change the recording source. This must be avoided because in practice no program does this correctly. In addition the only correct way doesn't work with the freeware OSS clones anyway.
Please look at the When OSS audio ioctl calls can be made section for information about DSP ioctl call ordering.
The return value from the OSS ioctl calls will be -1 if a fatal error occurred. Other values mean that the ioctl call was more or less successful. However in most cases the application must check the value returned in the argument to see what was the accepted value.
Please see the Possible error codes (errno) returned by OSS calls section for more info about the error codes returned by OSS.
| ossplay.c | Sources for the ossplay audio player and for the ossrecord |
| recsrc.c | A sample program for recording source selection |