7.28. ioctl VIDIOC_G_ENC_INDEX¶
7.28.1. Name¶
VIDIOC_G_ENC_INDEX - Get meta data about a compressed video stream
7.28.2. Synopsis¶
-
int
ioctl
(int fd, VIDIOC_G_ENC_INDEX, struct v4l2_enc_idx *argp)¶
7.28.3. Arguments¶
fd
- File descriptor returned by open().
argp
- Pointer to struct
v4l2_enc_idx
.
7.28.4. Description¶
The VIDIOC_G_ENC_INDEX ioctl provides meta data about a compressed video stream the same or another application currently reads from the driver, which is useful for random access into the stream without decoding it.
To read the data applications must call VIDIOC_G_ENC_INDEX with a
pointer to a struct v4l2_enc_idx
. On success
the driver fills the entry
array, stores the number of elements
written in the entries
field, and initializes the entries_cap
field.
Each element of the entry
array contains meta data about one
picture. A VIDIOC_G_ENC_INDEX call reads up to
V4L2_ENC_IDX_ENTRIES
entries from a driver buffer, which can hold up
to entries_cap
entries. This number can be lower or higher than
V4L2_ENC_IDX_ENTRIES
, but not zero. When the application fails to
read the meta data in time the oldest entries will be lost. When the
buffer is empty or no capturing/encoding is in progress, entries
will be zero.
Currently this ioctl is only defined for MPEG-2 program streams and video elementary streams.
-
v4l2_enc_idx
¶
__u32 | entries |
The number of entries the driver stored in the entry array. |
__u32 | entries_cap |
The number of entries the driver can buffer. Must be greater than zero. |
__u32 | reserved [4] |
Reserved for future extensions. Drivers must set the array to zero. |
struct v4l2_enc_idx_entry |
entry [V4L2_ENC_IDX_ENTRIES ] |
Meta data about a compressed video stream. Each element of the
array corresponds to one picture, sorted in ascending order by
their offset . |
-
v4l2_enc_idx_entry
¶
__u64 | offset |
The offset in bytes from the beginning of the compressed video stream to the beginning of this picture, that is a PES packet header as defined in ISO 13818-1 or a picture header as defined in ISO 13818-2. When the encoder is stopped, the driver resets the offset to zero. |
__u64 | pts |
The 33 bit Presentation Time Stamp of this picture as defined in ISO 13818-1. |
__u32 | length |
The length of this picture in bytes. |
__u32 | flags |
Flags containing the coding type of this picture, see Index Entry Flags. |
__u32 | reserved [2] |
Reserved for future extensions. Drivers must set the array to zero. |
V4L2_ENC_IDX_FRAME_I |
0x00 | This is an Intra-coded picture. |
V4L2_ENC_IDX_FRAME_P |
0x01 | This is a Predictive-coded picture. |
V4L2_ENC_IDX_FRAME_B |
0x02 | This is a Bidirectionally predictive-coded picture. |
V4L2_ENC_IDX_FRAME_MASK |
0x0F | AND the flags field with this mask to obtain the picture coding type. |
7.28.5. Return Value¶
On success 0 is returned, on error -1 and the errno
variable is set
appropriately. The generic error codes are described at the
Generic Error Codes chapter.