[FFmpeg-devel] 4:2:0 DV25 file wrongly identified as 4:1:1

[Michael Niedermayer]

On Fri, Sep 03, 2010 at 02:06:13PM +0200, Niobos wrote:
> Hi,
> 
> I'm trying to pin down an issue we're having decoding a DV25 stream. The
> problem seems to be that ffmpeg (libavcodec to be more precise) thinks
> the content is in SMPTE314M 4:1:1 format, while it actually is in
> IEC61834 4:2:0 format. I'm not sure that ffmpeg is wrong; the file does
> look fishy too...
> 
> 
> First some context from the libavcodec's point of view:
> 
> The corresponding if-statement seems to be located here:
> libavcodec/dvdata.c:258
>    /* 576i50 25Mbps 4:1:1 is a special case */
>    if (dsf == 1 && stype == 0 && frame[5] & 0x07) {
>        return &dv_profiles[2];
>    }
> Especially the last condition checking frame[5]'s lower 3 bits.
> 
> This line dates back from commit
> 69afa85bf7cb5e3491efdd088d7b5067a2858d6d, but the logic is much older. I
> traced it back through GIT (sorry, I'm a little more familiar with GIT
> than with SVN): (recent to old)
> * 69afa85bf7cb5e3491efdd088d7b5067a2858d6d
> * fe4d60d52c7ba06b5d035db6660820dc07c45272
> * ba65fac202644cce948a7f11bd27759499213d1c
> * 691af50dbdf7262aa732b1a2eab42fb2f6873316
> 
> During the beginning of its lifetime, it was commented as "APT flag",
> but that comment was lost on the last commit (69afa).
> 
> 
> The DV-stream contains the following Application ID fields:
> APT=0b000 AP1=0b001 AP2=0b001 AP3=0b001
> 
> SMPTE314M states that four 0b000 values indicate IEC parameters (4:2:0,
> correct in this case); while four 0b001 values indicate SMPTE parameters
> (4:1:1, incorrect in this case). Clearly, this file conforms to none of
> these defined sets.
> 
> 
> The reason why I'm raising this issue here (as well as with the tool
> that produced the file), is that a simple fix (attached) will:
> * make ffmpeg work for our production system
> * conform to the original comment (which is now lost) by checking the
> APT flag instead of the AP1 flag.
> 
> Obviously, this change may break DV decoding if the current behaviour is
> desired. I'm no expert on the DV format, comments and insights are welcome.
> 
> Greetings,
> Niobos

>  dvdata.c |    2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 24b14fe94c5cfd32b6d52ee8660360dc63f67594  dv25-wrongly-identified-as-411.patch

as noone wants to maintain dv ...
patch should be ok if tested & passes fate 

[...]
-- 
Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

When the tyrant has disposed of foreign enemies by conquest or treaty, and
there is nothing more to fear from them, then he is always stirring up
some war or other, in order that the people may require a leader. -- Plato
-------------- next part --------------
A non-text attachment was scrubbed...
Name: not available
Type: application/pgp-signature
Size: 198 bytes
Desc: Digital signature
URL: <http://lists.mplayerhq.hu/pipermail/ffmpeg-devel/attachments/20100921/9a20ad10/attachment.pgp>