Em 28-05-2011 12:24, Hans Verkuil escreveu:
> But I would really like to see an RFC with a proposal of the API and how
> it is to be used. Then after an agreement has been reached the library can
> be modified accordingly and we can release it.
Ok, that's the RFC for the API. The code is already committed, on a separate
library at v4l-utils. So, feel free to test.
1) Media enumberation library
==========================
/**
* enum device_type - Enumerates the type for each device
*
* The device_type is used to sort the media devices array.
* So, the order is relevant. The first device should be
* V4L_VIDEO.
*/
enum device_type {
UNKNOWN = 65535,
NONE = 65534,
V4L_VIDEO = 0,
V4L_VBI,
DVB_FRONTEND,
DVB_DEMUX,
DVB_DVR,
DVB_NET,
DVB_CA,
/* TODO: Add dvb full-featured nodes */
SND_CARD,
SND_CAP,
SND_OUT,
SND_CONTROL,
SND_HW,
};
/**
* discover_media_devices() - Returns a list of the media devices
* @md_size: Returns the size of the media devices found
*
* This function reads the /sys/class nodes for V4L, DVB and sound,
* and returns an opaque desciptor that keeps a list of the devices.
* The fields on this list is opaque, as they can be changed on newer
* releases of this library. So, all access to it should be done via
* a function provided by the API. The devices are ordered by device,
* type and node. At return, md_size is updated.
*/
void *discover_media_devices(void);
/**
* free_media_devices() - Frees the media devices array
*
* @opaque: media devices opaque descriptor
*
* As discover_media_devices() dynamically allocate space for the
* strings, feeing the list requires also to free those data. So,
* the safest and recommended way is to call this function.
*/
void free_media_devices(void *opaque);
/**
* display_media_devices() - prints a list of media devices
*
* @opaque: media devices opaque descriptor
*/
void display_media_devices(void *opaque);
/**
* get_not_associated_device() - Return the next device not associated with
* an specific device type.
*
* @opaque: media devices opaque descriptor
* @last_seek: last seek result. Use NULL to get the first result
* @desired_type: type of the desired device
* @not_desired_type: type of the seek device
*
* This function seeks inside the media_devices struct for the next physical
* device that doesn't support a non_desired type.
* This method is useful for example to return the audio devices that are
* provided by the motherboard.
*/
char *get_associated_device(void *opaque,
char *last_seek,
enum device_type desired_type,
char *seek_device,
enum device_type seek_type);
/**
* get_associated_device() - Return the next device associated with another one
*
* @opaque: media devices opaque descriptor
* @last_seek: last seek result. Use NULL to get the first result
* @desired_type: type of the desired device
* @seek_device: name of the device with you want to get an association.
*@ seek_type: type of the seek device. Using NONE produces the same
* result of using NULL for the seek_device.
*
* This function seeks inside the media_devices struct for the next device
* that it is associated with a seek parameter.
* It can be used to get an alsa device associated with a video device. If
* the seek_device is NULL or seek_type is NONE, it will just search for
* devices of the desired_type.
*/
char *get_not_associated_device(void *opaque,
char *last_seek,
enum device_type desired_type,
enum device_type not_desired_type);
2) Example showing the typical usecase
===================================
#include "../libmedia_dev/get_media_devices.h"
#include <stdio.h>
int main(void)
{
void *md;
char *alsa;
md = discover_media_devices();
display_media_devices(md);
alsa = get_associated_device(md, NULL, SND_CAP, "video0", V4L_VIDEO);
if (alsa)
printf("Alsa device associated with video0 capture: %s\n", alsa);
alsa = get_not_associated_device(md, NULL, SND_OUT, V4L_VIDEO);
if (alsa)
printf("Alsa output device: %s\n", alsa);
free_media_devices(md);
return 0;
}
3) Planned improvements
====================
a) To create a new functions similar to get_associated_device, that uses an opened
file descriptor for device association;
b) provide a method to return /dev names for applications.
Cheers,
Mauro
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