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aizvorski / h264bitstream

A complete set of functions to read and write H.264 video bitstreams, in particular to examine or modify headers.
GNU Lesser General Public License v2.1
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h264_sei.c: parse multiple SEI messages properly #1

Closed paintcan closed 10 years ago

paintcan commented 10 years ago

SEI NALU containing multiple messages: 00 00 00 01 06 01 01 04 04 09 b5 00 31 44 54 47 31 41 f8 06 01 84 80

read_sei_payload currently invokes read_sei_end_bits, ultimately invoking read_rbsp_trailing_bits after parsing a single message. However, h264_read_sei_rbsp in h264_stream.c invokes this function multiple times to read every SEI message inside the SEI NALU. h264_read_rbsp_trailing_bits is invoked after that loop, and it's clear that's the proper place for it to be called, rather than after reading each individual SEI message.

The impact of the bug is that h264_analyze dumps a garbled description of subsequent SEI messages when more than one is present, as the payload type and size for each is read from the wrong bytes. Commenting out this one line has fixed the issue for me locally, but I don't have the understanding of the entire project required to determine if this change fixes one issue but breaks the intentions of the code elsewhere.

Thanks for the project by the way, it is awesome!

aizvorski commented 10 years ago

Paintcan: Thank you for finding this. Looks like the root of the problem was calling read_rbsp_trailing_bits() from read_sei_end_bits() every time. Your patch is fine though, may need to adjust later when adding support for specific SEI message types. Thanks!