[FFmpeg-devel] [PATCH 2/2] avformat/mpegts: Skip over broken 0x80 headers

Kieran Kunhya kierank at obe.tv
Wed Apr 27 22:29:40 CEST 2016

On Wed, 27 Apr 2016 at 11:32 Mark Thompson <sw at jkqxz.net> wrote:

> On 24/04/16 23:24, Michael Niedermayer wrote:
> > On Sun, Apr 24, 2016 at 11:27:32AM +0100, Mark Thompson wrote:
> >> On 24/04/16 03:53, Michael Niedermayer wrote:
> >>> 0x47 is expected to be at [0] but the affected files contain something
> >>> else sometimes in its place that starts with 0x80 and is 12 bytes long
> >>> it contains some counter or timestamp
> >>> without the code above it will almost always work but if the counter
> >>> contains a 0x47 in it resync can start at the wrong byte
> >>>
> >>> I dont know what created these kind of files, so even if iam not
> >>> hit by a bus i think i am not too usefull here
> >>> i was hoping a bit my patch would lead to someone recognizing this ...
> >>
> >> Sounds like an RTP header.  (You can certainly imagine a very sucky RTP
> receiver not bothering to do anything with the headers and hoping it all
> works out.)
> >>
> >> Is it a 16-bit counter in the third and fourth bytes, and a 32-bit
> timestamp in the fifth to eighth?  <
> https://tools.ietf.org/html/rfc3550#section-5>
> >>
> >> (Alternatively, link me to the sample and I'll have a look at it.)
> >
> > http://samples.ffmpeg.org/ts/01c56b0dc1.ts
> Hmm.  So it does look like an RTP header, with the version correct,
> payload type for MPEG-TS and the sequence number in the right place.
> However, the timestamp and SSRC are always zero, and it lacks the subheader
> required by RFC 2250 for this sort of MPEG-TS-in-RTP stream.
> I don't see how you could sanely create a file like this - it's like
> someone has heard of RTP and thinks they should put RTP headers on things
> without actually considering what they mean.
> Unless someone can show what created this file and that it might make
> more, I suggest that the hack workaround should be removed.  The simple
> scan for 0x47 is a more consistent behaviour in the presence of broken
> files, even though it doesn't work in this particular case.
> Thanks,
> - Mark
I agree, this isn't a TS file and so the demuxer shouldn't be able to
handle it without handling wireshark dumps etc. I'm not aware on any
further headers required for TS in RTP however.


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