[FFmpeg-devel] Collection of patches

[Michael Niedermayer]

On Wed, Apr 23, 2008 at 09:36:21PM +0100, M?ns Rullg?rd wrote:
> Michael Niedermayer <michaelni at gmx.at> writes:
> 
> > On Wed, Apr 23, 2008 at 01:55:13PM +0200, Thorsten Jordan wrote:
> >> Michael Niedermayer schrieb:
> >> > On Wed, Apr 23, 2008 at 09:15:40AM +0200, Thorsten Jordan wrote:
> >> >> Michael Niedermayer schrieb:
> >> >>> On Tue, Apr 22, 2008 at 12:36:02PM +0200, Thorsten Jordan wrote:
> >> >>> [...]
> >> >>>> So thanks for reading so far and here are the patches:
> >> >>>>
> >> >>>> Make AVCHD (mts) files give better PTS values, as PCR packets are
> >> >>>> scanned ignoring the mts<->ts difference:
> >> >>>> mts_pcr_parse_syncbyte_check.patch
> >> >>> mans ?
> >> >> it may look a bit hackish but shows up a problem when decoding .mts
> >> >> files, as they are not handled specially by ffmpeg. The TS demuxer just
> >> >> scans for the next 0x47 startcode, skipping the 4 bytes of the counter
> >> >> that are stored in each mts-"packet" before the TS part. Since the first
> >> >> byte of that counter is <= 0x3f, that patch should be valid (it can
> >> >> never be 0x47). Imho the demuxer should handle mts specially, because
> >> >> what if any of the bytes 1-3 of that counter are 0x47 by coincidence?
> >> > 
> >> > Now your patch looks really wrong. Where can i find a .mts file?
> >> I have uploaded a file avchd_camera_testfile.mts to subdirectory
> >> avchd_camera_testfile in MPlayer/incoming like as for a bugreport.
> >
> > thanks
> >
> >> 
> >> MTS has 192-byte-sized packets, of which the first four bytes are a big
> >> endian counter (some kind of time stamp, like pcr) and the rest 188
> >> bytes are a normal TS packet. The exact meaning of the counter is
> >> unknown to me and I couldn't find info on the net. The
> >> open-source-software "TSMuxeR" writes a copy of the PCR to it, like when
> >> streaming TS/HDV to a camera, however the lower nibbles of the counter
> >> look like they have a special meaning, like isochronous packets on
> >> firewire transport.
> >> 
> >> Imho it would be best to write a dedicated mts demuxer that uses the ts
> >> demuxer, but "knows" of the gaps between TS packets.
> >
> > Iam really scared
> >
> >> 
> >> My patch checks if the first byte of the buffer is 0x47 (always true for
> >> ts) and if not to advance 4 bytes (it assumes mts then), and decode the
> >> PCR from there.
> >
> > Nonsense, the problem has nothing to do with mts
> > This is about packets not begining exactly at the file start
> > the same will happen with any random ts file that has been cut by dd.
> > Our naive seeking code assumes packets do start exactly at the file
> > start, the idea to fix the case where its exactly 4 bytes off in a hack like
> > you do is insane. ... And the idea to write a seperate demuxer for that is
> > even more insane.
> >
> > Proper fix below (which i will apply in 24h unless mans objects)
> >
> > Index: libavformat/mpegts.c
> > ===================================================================
> > --- libavformat/mpegts.c	(revision 12867)
> > +++ libavformat/mpegts.c	(working copy)
> > @@ -90,6 +90,9 @@
> >      AVFormatContext *stream;
> >      /** raw packet size, including FEC if present            */
> >      int raw_packet_size;
> > +
> > +    int pos47;
> > +
> >      /** if true, all pids are analyzed to find streams       */
> >      int auto_guess;
> >
> > @@ -1046,6 +1049,8 @@
> >      if (p >= p_end)
> >          return;
> >
> > +    ts->pos47= url_ftell(ts->stream->pb) % ts->raw_packet_size;
> > +
> >      if (tss->type == MPEGTS_SECTION) {
> >          if (is_start) {
> >              /* pointer field present */
> > @@ -1379,7 +1384,7 @@
> >      uint8_t buf[TS_PACKET_SIZE];
> >      int pcr_l, pcr_pid = ((PESContext*)s->streams[stream_index]->priv_data)->pcr_pid;
> >      const int find_next= 1;
> > -    pos = ((*ppos  + ts->raw_packet_size - 1) / ts->raw_packet_size) * ts->raw_packet_size;
> > +    pos = ((*ppos  + ts->raw_packet_size - 1 - ts->pos47) / ts->raw_packet_size) * ts->raw_packet_size + ts->pos47;
> >      if (find_next) {
> >          for(;;) {
> >              url_fseek(s->pb, pos, SEEK_SET);
> 
> OK, and thanks.

patch applied :)

[...]
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Michael     GnuPG fingerprint: 9FF2128B147EF6730BADF133611EC787040B0FAB

Many that live deserve death. And some that die deserve life. Can you give
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