On Sat, Mar 25, 2017 at 9:01 AM, Steven Liu <l...@chinaffmpeg.org> wrote:
> refer to SPEC:
> Annex E. The FLV File Format said:
> E.3 TheFLVFileBody have a table:
> Field Type Comment
> PreviousTagSize0 UI32 Always 0
>
> Signed-off-by: Steven Liu <l...@chinaffmpeg.org>
> ---
> libavformat/flvdec.c | 13 ++++++++++++-
> 1 file changed, 12 insertions(+), 1 deletion(-)
>
> diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
> index cdcfb9c..ac74b45 100644
> --- a/libavformat/flvdec.c
> +++ b/libavformat/flvdec.c
> @@ -709,6 +709,7 @@ static int flv_read_header(AVFormatContext *s)
> int flags;
> FLVContext *flv = s->priv_data;
> int offset;
> + int pre_tag_size = 0;
>
> avio_skip(s->pb, 4);
> flags = avio_r8(s->pb);
> @@ -719,7 +720,17 @@ static int flv_read_header(AVFormatContext *s)
>
> offset = avio_rb32(s->pb);
> avio_seek(s->pb, offset, SEEK_SET);
> - avio_skip(s->pb, 4);
> +
> + /* Annex E. The FLV File Format
> + * E.3 TheFLVFileBody
> + * Field Type Comment
> + * PreviousTagSize0 UI32 Always 0
> + * */
> + pre_tag_size = avio_rb32(s->pb);
> + if (pre_tag_size) {
> + av_log(s, AV_LOG_ERROR, "Read FLV header error, input file is not a
> standard flv format, first PreviousTagSize0 always is 0\n");
> + return AVERROR_INVALIDDATA;
> + }
>
What does this exactly break if its not 0?
Demuxers should try to be forgiving on non-standard files, so checking
some spec limitation like that only makes sense if it has an actual
impact on playability of the file.
- Hendrik
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