[FFmpeg-devel] [PATCH v2] avformat/flvdec: check FLVHeader PreviousTagSize0

[Steven Liu]

2017-03-26 18:39 GMT+08:00 Bodecs Bela <bodecsb at vivanet.hu>:

>
>
> 2017.03.25. 14:15 keltezéssel, Steven Liu írta:
>
>> 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 <lq at chinaffmpeg.org>
>> ---
>>   libavformat/flvdec.c | 12 +++++++++++-
>>   1 file changed, 11 insertions(+), 1 deletion(-)
>>
>> diff --git a/libavformat/flvdec.c b/libavformat/flvdec.c
>> index cdcfb9c..94c9e28 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 +720,16 @@ 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_WARNING, "Read FLV header error, input file is
>> not a standard flv format, first PreviousTagSize0 always is 0\n");
>> +    }
>>         s->start_time = 0;
>>       flv->sum_flv_tag_size = 0;
>>
> I think this forgiving behaviour is better, than the earlier rigorous one.
> I agree that showing warning is more useful than returning error and
> stopping execution because if
>
> PreviousTagSize0 is not zero that causes no harm.
>
> bb
>
>
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Pushed



Thanks!