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
| __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. | ||
Table 2. struct 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 Table 3. |
| __u32 | reserved[2] | Reserved for future extensions. Drivers must set the array to zero. |
Table 3. Index Entry Flags
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. |