mirror of
https://git.ffmpeg.org/ffmpeg.git
synced 2026-01-01 11:50:01 +01:00
8bd66a8c95
The criteria for slice structure validity is similar to that of subpicture structure validity that we saw not too long ago [1]. The relationship between tiles and slices must satisfy the following properties: * Exhaustivity. All tiles in a picture must belong to a slice. The tiles cover the picture, so this implies the slices must cover the picture. * Mutual exclusivity. No tile may belong to more than one slice, i.e. slices may not overlap. In most cases these properties are guaranteed by the syntax. There is one noticable exception however: when pps_tile_idx_delta_present_flag is equal to one, each slice is associated with a syntax element pps_tile_idx_delta_val[i] which "specifies the difference between the tile index of the tile containing the first CTU in the ( i + 1 )-th rectangular slice and the tile index of the tile containing the first CTU in the i-th rectangular slice" [2]. When these syntax elements are present, the i-th slice can begin anywhere and the usual guarantees provided by the syntax are lost. The patch detects slice structures which violate either of the two properties above, and are therefore invalid, while building the slice map. Should the slice map be determined to be invalid, an AVERROR_INVALIDDATA is returned. This prevents issues including segmentation faults when trying to decode, invalid bitstreams. [1]: https://ffmpeg.org//pipermail/ffmpeg-devel/2024-October/334470.html [2]: H.266 (V3) Section 7.4.3.5, Picture parameter set RBSP semantics Signed-off-by: Frank Plowman <post@frankplowman.com>