[FFmpeg-devel] [PATCH] asfdemux: wrong padding

Michael Niedermayer michaelni
Mon Nov 17 00:25:17 CET 2008

On Sun, Nov 16, 2008 at 05:55:14PM -0500, Ronald S. Bultje wrote:
> Hi,
> There's this code in asf.c, line 626:
>     if (packet_length < asf->hdr.min_pktsize)
>         padsize += asf->hdr.min_pktsize - packet_length;
> What it does is to make sure that if the packet_length field is not
> within the range of the min/max_pktsize specified in the ASF header,
> we skip the rest as if it were padding. I suppose this fixes playback
> of some files but I'm not completely sure.
> Here's a quote from the specifications [1]:
> "Minimum Data Packet Size
> Specifies the minimum Data Packet size in bytes. In general, the value
> of this field is invalid if the Broadcast Flag bit in the Flags field
> is set to 1. However, for the purposes of this specification, the
> values for the Minimum Data Packet Size and Maximum Data Packet Size
> fields shall be set to the same value, and this value should be set to
> the packet size, even when the Broadcast Flag in the Flags field is
> set to 1."
> This particular bit of code causes issues for broadcasted, non-file
> data (i.e. broadcast-flag=1 in the ASF header). These don't have a
> fixed packet size but rather use the packet_length field that is
> directly at the start of the ASF packet (line 600 of asf.c). As said
> in the quote, in these broadcast streams, min_pktsize == max_pktsize
> and these values are bigger than the actual ASF packets, with no
> padding present.
> I suggest the attached patch for asf.c to not pad the input stream if
> the broadcast flag is set. With this patch applied, I can cat the ASF
> file header (in the SDP) plus the ASF packet data from each RTSP
> packet (minus a small MS-extension header) and I in fact get an ASF
> file that can be played back using ffplay. (And yes, I'm working on
> MS-RTSP and it partly works, I need to do some heavy refatoring in
> asf.c before that can be submitted...)

this patch needs to be tested against asf/wmv/wma/dvr-ms files
i think ive never seen a asf file with a packet size < min
though iam not surprised by MSs asshattry of redefining min & max and using
smaller packets

btw, does seeking work?

Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

> ... defining _GNU_SOURCE...
For the love of all that is holy, and some that is not, don't do that.
-- Luca & Mans
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 189 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20081117/f004c0c1/attachment.pgp>

More information about the ffmpeg-devel mailing list