VIDIOC_G_ENC_INDEX -- Get meta data about a compressed video stream


int ioctl(int fd, int request, struct v4l2_enc_idx *argp);



File descriptor returned by open().





Experimental: This is an experimental interface and may change in the future.

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.

Table 1. struct v4l2_enc_idx

__u32entriesThe number of entries the driver stored in the entry array.
__u32entries_capThe number of entries the driver can buffer. Must be greater than zero.
__u32reserved[4]Reserved for future extensions. Drivers must set the array to zero.
struct v4l2_enc_idx_entryentry[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.

Table 2. struct v4l2_enc_idx_entry

__u64offsetThe 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.
__u64ptsThe 33 bit Presentation Time Stamp of this picture as defined in ISO 13818-1.
__u32lengthThe length of this picture in bytes.
__u32flagsFlags containing the coding type of this picture, see Table 3.
__u32reserved[2]Reserved for future extensions. Drivers must set the array to zero.

Table 3. Index Entry Flags

V4L2_ENC_IDX_FRAME_I0x00This is an Intra-coded picture.
V4L2_ENC_IDX_FRAME_P0x01This is a Predictive-coded picture.
V4L2_ENC_IDX_FRAME_B0x02This is a Bidirectionally predictive-coded picture.
V4L2_ENC_IDX_FRAME_MASK0x0FAND the flags field with this mask to obtain the picture coding type.

Return Value

On success 0 is returned, on error -1 and the errno variable is set appropriately:


The driver does not support this ioctl.