Overview¶
We discuss here how to import items to create HEIF file collections. For track import, use the regular tools from GPAC.
Importing images¶
You can use MP4Box to manually import each item, see MP4Box -h meta.
When importing images, the first image imported will be set as primary item if the destination file has no primary item.
To import a single key frame src.hvc source:
To import a key frame at a given time from a source video:
MP4Box can also import several images at once.
To import all key frames from a source video:
To import all key frames start time 3 sec to end time 22.5 second in a source video:
To import all key frames every 30 seconds in a source video:
To import all key frames every 30 seconds from start time 3 sec to end time 3min in a source video:
Filtering while importing¶
MP4Box can be used together with filters in gpac, as discussed here. This section illustrates how this feature can be used in various use cases.
Importing a subset of frames¶
The following example import frames 1, 12 and 15 from a source sequence using the reframer filter:
Importing and transcoding¶
The following example imports a JPG image and transcodes it to HEVC at 5 mbps:
Creating images in a file with video¶
MP4Box can create images from a file with one or more video tracks and save the combined video+items.
The syntax used is the same as the examples above except the source file is not set.
The video track to import from can be set using tkID option, otherwise the first video track will be used.
To import a key frame at a given sample position as item:
To import all key frames as items position (here renaming the output file from mp4 to heif):
In the above examples, the video data is copied to the new item, which increases the file size.
You can change that by specifying that the item is a reference to the sample data using ref:
In this example, the first key frame of every 30s window of the source track will be added as an item sharing the data with the track sample.
Creating grids¶
Grids can be created using add-image-grid, as illustrated in these tests.
There is also a quick grid creation option called agrid which automatically computes a grid from the items present in the file.
It will hide all these items and make the grid a primary item, resulting in a thumbnail-like grid picture.
All images in the file must have the same width and height. If the number of images is not even, the last image will be ignored.
This will create a new file containing the first key frame of every 30s window of long_video.mp4 and add a grid representing all these items.
The grid aspect ratio can be hinted using agrid=AR , with AR the target aspect ratio. There is no guarantee that the AR will be respected since this depends on the image source sizes and number.