[FFmpeg-devel] libavformat/mpegtsenc: adaptive alignment for teletext PES packets

Submitted by Andreas Håkon on May 22, 2019, 3:04 p.m.

Details

Message ID Q0IPCda6ob8F1JXMRok09-osmyBWUTNVIf1HvwL-xbg1qQZeQLT5JedArz3AWP0VxcaWocHKlZs7VuRUUAuWln-rL08DpwupnK9GToS5Qmg=@protonmail.com
State New
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Commit Message

Andreas Håkon May 22, 2019, 3:04 p.m.
Hi,

Patch to generate aligned Teletext PES packets using the MPEG-TS muxer
when the TS header contains data.

Regards.
A.H.

---
From 5b476153e0fcced53afa1b77543c2e386f08c504 Mon Sep 17 00:00:00 2001
From: Andreas Hakon <andreas.hakon@protonmail.com>
Date: Wed, 22 May 2019 15:36:50 +0100
Subject: [PATCH] libavformat/mpegtsenc: adaptive alignment for teletext PES
 packets

The code that generates the PES packets for Teletext data aligns the PES packets
with the boundaries of the TS packets. The strategy used is to insert padding
stuff into the PES header. The size of this padding alignment currently has a
fixed size of 36 bytes. And this value is correct when all of the Teletext
TS packets have payload only. However, inserting some data into the TS header
breaks this assumption. In this case, the Teletext PES packets are not aligned
and the end of the PES packet is inserted into an additional TS packet with a
large amount of TS padding.

This patch calculates the size of the TS header in order to reduce the size of
the PES padding and thus accommodate the PES packet to the TS boundaries.
In this way no additional TS packets are produced.

Signed-off-by: Andreas Hakon <andreas.hakon@protonmail.com>
 libavformat/mpegtsenc.c |    7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

--
1.7.10.4

Comments

Andreas Håkon May 28, 2019, 11:04 a.m.
Hi,

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Wednesday, 22 de May de 2019 17:04, Andreas Håkon <andreas.hakon@protonmail.com> wrote:

> Patch to generate aligned Teletext PES packets using the MPEG-TS muxer
> when the TS header contains data.

Can someone please tell me who is the official maintainer of the MPEG-TS muxer?
I'm still waiting for comments regarding this patch.
We've been using it for a long time without problems.

Regards.
A.H.

---
Andreas Rheinhardt May 28, 2019, 11:24 a.m.
Andreas Håkon:
> Hi,
> 
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Wednesday, 22 de May de 2019 17:04, Andreas Håkon <andreas.hakon@protonmail.com> wrote:
> 
>> Patch to generate aligned Teletext PES packets using the MPEG-TS muxer
>> when the TS header contains data.
> 
> Can someone please tell me who is the official maintainer of the MPEG-TS muxer?
> I'm still waiting for comments regarding this patch.
> We've been using it for a long time without problems.
Just take a look into the MAINTAINERS file:

mpegts.c      Marton Balint
mpegtsenc.c   Baptiste Coudurier

- Andreas
Andreas Håkon May 28, 2019, 12:08 p.m.
Hi A. Rheinhardt,


‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Tuesday, 28 de May de 2019 13:24, Andreas Rheinhardt <andreas.rheinhardt@gmail.com> wrote:

> > Can someone please tell me who is the official maintainer of the MPEG-TS muxer?
> > I'm still waiting for comments regarding this patch.
> > We've been using it for a long time without problems.
>
> Just take a look into the MAINTAINERS file:
>
> mpegts.c Marton Balint
> mpegtsenc.c Baptiste Coudurier

I do that! More than two weeks ago I send a private message to B. Coudurier (free.fr) mail.
However, I think that address doesn't work.

I hope someone can review and merge this patch.
Sorry for disturbing you.

Regards.
A.H.

---
Andreas Rheinhardt May 28, 2019, 12:36 p.m.
Andreas Håkon:
> Hi A. Rheinhardt,
> 
> 
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Tuesday, 28 de May de 2019 13:24, Andreas Rheinhardt <andreas.rheinhardt@gmail.com> wrote:
> 
>>> Can someone please tell me who is the official maintainer of the MPEG-TS muxer?
>>> I'm still waiting for comments regarding this patch.
>>> We've been using it for a long time without problems.
>>
>> Just take a look into the MAINTAINERS file:
>>
>> mpegts.c Marton Balint
>> mpegtsenc.c Baptiste Coudurier
> 
> I do that! More than two weeks ago I send a private message to B. Coudurier (free.fr) mail.
> However, I think that address doesn't work.
His emails to this list are sent from baptiste.coudurier@gmail.com.

- Andreas
Michael Niedermayer May 28, 2019, 5:11 p.m.
On Tue, May 28, 2019 at 12:08:55PM +0000, Andreas Håkon wrote:
> Hi A. Rheinhardt,
> 
> 
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Tuesday, 28 de May de 2019 13:24, Andreas Rheinhardt <andreas.rheinhardt@gmail.com> wrote:
> 
> > > Can someone please tell me who is the official maintainer of the MPEG-TS muxer?
> > > I'm still waiting for comments regarding this patch.
> > > We've been using it for a long time without problems.
> >
> > Just take a look into the MAINTAINERS file:
> >
> > mpegts.c Marton Balint
> > mpegtsenc.c Baptiste Coudurier
> 
> I do that! More than two weeks ago I send a private message to B. Coudurier (free.fr) mail.
> However, I think that address doesn't work.
> 
> I hope someone can review and merge this patch.
> Sorry for disturbing you.

with which software has the generated mpeg-ts been tested ?
do you have any testecases ?

thanks

[...]
Andreas Håkon May 28, 2019, 5:48 p.m.
Hi Michael,

> with which software has the generated mpeg-ts been tested ?
> do you have any testecases ?

Our test cases are mainly DVB-C broadcasts and mobile streaming.
All clients play well. And internal testing is done using the
well-known DVB Inspector.

Regards.
A.H.

---
Michael Niedermayer May 29, 2019, 7:20 p.m.
On Tue, May 28, 2019 at 05:48:27PM +0000, Andreas Håkon wrote:
> Hi Michael,
> 
> > with which software has the generated mpeg-ts been tested ?
> > do you have any testecases ?
> 
> Our test cases are mainly DVB-C broadcasts and mobile streaming.
> All clients play well. And internal testing is done using the
> well-known DVB Inspector.

adding information about testing or other things that increase the
confidence of a reviewer that a change is correct should decrease
the time until its applied

thx

[...]
Marton Balint June 1, 2019, 11:38 p.m.
On Wed, 22 May 2019, Andreas Håkon wrote:

> Hi,
>
> Patch to generate aligned Teletext PES packets using the MPEG-TS muxer
> when the TS header contains data.
>

> The code that generates the PES packets for Teletext data aligns the PES packets
> with the boundaries of the TS packets. The strategy used is to insert padding
> stuff into the PES header. The size of this padding alignment currently has a
> fixed size of 36 bytes. And this value is correct when all of the Teletext
> TS packets have payload only. However, inserting some data into the TS header
> breaks this assumption. In this case, the Teletext PES packets are not aligned
> and the end of the PES packet is inserted into an additional TS packet with a
> large amount of TS padding.

What is the data that is inserted into the TS header? Can you give an 
example? Are you sure that it is allowed to generate such streams? 
Are you seeing such streams in the wild?

The DVB teletext spec is very strict about that PES header size and 0x24 
is hardcoded there.

https://www.etsi.org/deliver/etsi_en/300400_300499/300472/01.03.01_60/en_300472v010301p.pdf

So maybe you should use adaptation field stuffing instead to keep the 
alignment?

> 
> This patch calculates the size of the TS header in order to reduce the size of
> the PES padding and thus accommodate the PES packet to the TS boundaries.
> In this way no additional TS packets are produced.
> 
> Signed-off-by: Andreas Hakon <andreas.hakon@protonmail.com>
>  libavformat/mpegtsenc.c |    7 +++++--
>  1 file changed, 5 insertions(+), 2 deletions(-)
> 
> diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
> index fc0ea22..f1772ac 100644
> --- a/libavformat/mpegtsenc.c
> +++ b/libavformat/mpegtsenc.c
> @@ -1328,8 +1328,11 @@ static void mpegts_write_pes(AVFormatContext *s, AVStream *st,
>                          header_len += 3;
>              }
>              if (is_dvb_teletext) {
> -                pes_header_stuffing_bytes = 0x24 - header_len;
> -                header_len = 0x24;
> +                int header_stuff = (get_ts_payload_start(buf) - buf) - 4;

This is a very bad variable name. Call it adaptation_field_len.

> +                if (header_stuff - header_len > 0x24)
> +                    header_stuff = 0;

Are you sure about this check?

> +                pes_header_stuffing_bytes = 0x24 - header_len - header_stuff;
> +                header_len = 0x24 - header_stuff;
>              }
>              len = payload_size + header_len + 3;
>              /* 3 extra bytes should be added to DVB subtitle payload: 0x20 0x00 at the beginning and trailing 0xff */
> --
> 1.7.10.4

Regards,
Marton
Andreas Håkon June 4, 2019, 9:26 a.m.
Hi Marton,


Thank you for taking the time to review this patch!

‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
On Sunday, 2 de June de 2019 1:38, Marton Balint <cus@passwd.hu> wrote:

> On Wed, 22 May 2019, Andreas Håkon wrote:
>
> > Hi,
> > Patch to generate aligned Teletext PES packets using the MPEG-TS muxer
> > when the TS header contains data.
>
> > The code that generates the PES packets for Teletext data aligns the PES packets
> > with the boundaries of the TS packets. The strategy used is to insert padding
> > stuff into the PES header. The size of this padding alignment currently has a
> > fixed size of 36 bytes. And this value is correct when all of the Teletext
> > TS packets have payload only. However, inserting some data into the TS header
> > breaks this assumption. In this case, the Teletext PES packets are not aligned
> > and the end of the PES packet is inserted into an additional TS packet with a
> > large amount of TS padding.
>
> What is the data that is inserted into the TS header? Can you give an
> example? Are you sure that it is allowed to generate such streams?
> Are you seeing such streams in the wild?

It can vary. For example you can add PCR timestamps inside the Teletext stream
(not very common, but possible).


> The DVB teletext spec is very strict about that PES header size and 0x24
> is hardcoded there.
>
> https://www.etsi.org/deliver/etsi_en/300400_300499/300472/01.03.01_60/en_300472v010301p.pdf

Yes, you're right. The sentence at section "4.2 PES packet format" indicates:

"PES_header_data_length set to "0x24"." And after it adds:

"PTS and other optional fields may be present in the PES header,
but the header length is always fixed for streams
identified in the Program Specific Information (PSI) by the DVB Teletext descriptor"

However, the idea of this restriction is to leave space for PTS data even if
it's not present in the PES packet. And if you don't add any additional stuff
in the TS header, the constraint is satisfied.

Perhaps you'd prefer this behavior to be optional?


> So maybe you should use adaptation field stuffing instead to keep the
> alignment?

This is already being done.
The objective is to use the empty space of the PES header when there is data
in the TS header, maintaining the original alignment.


> > +                  int header_stuff = (get_ts_payload_start(buf) - buf) - 4;
>
> This is a very bad variable name. Call it adaptation_field_len.

OK.

> > +                  if (header_stuff - header_len > 0x24)
> > +                      header_stuff = 0;
>
> Are you sure about this check?

YES. When no free space in the PES header then the code is disabled (equivalent
to "adaptation_field_len"/"header_stuff" = 0)... see this line:

> > +                  header_len = 0x24 - header_stuff;

And the aligment of the last TS packet is done using TS header stuffing.


So, please Marton, comment if you prefer:
- Change only the ugly name of the var.
- Make behaviour optional.
- Discard the patch.

Regards.
A.H.

---
Marton Balint June 4, 2019, 5:03 p.m.
On Tue, 4 Jun 2019, Andreas Håkon wrote:

> Hi Marton,
>
>
> Thank you for taking the time to review this patch!
>
> ‐‐‐‐‐‐‐ Original Message ‐‐‐‐‐‐‐
> On Sunday, 2 de June de 2019 1:38, Marton Balint <cus@passwd.hu> wrote:
>
>> On Wed, 22 May 2019, Andreas Håkon wrote:
>>
>> > Hi,
>> > Patch to generate aligned Teletext PES packets using the MPEG-TS muxer
>> > when the TS header contains data.
>>
>> > The code that generates the PES packets for Teletext data aligns the PES packets
>> > with the boundaries of the TS packets. The strategy used is to insert padding
>> > stuff into the PES header. The size of this padding alignment currently has a
>> > fixed size of 36 bytes. And this value is correct when all of the Teletext
>> > TS packets have payload only. However, inserting some data into the TS header
>> > breaks this assumption. In this case, the Teletext PES packets are not aligned
>> > and the end of the PES packet is inserted into an additional TS packet with a
>> > large amount of TS padding.
>>
>> What is the data that is inserted into the TS header? Can you give an
>> example? Are you sure that it is allowed to generate such streams?
>> Are you seeing such streams in the wild?
>
> It can vary. For example you can add PCR timestamps inside the Teletext stream
> (not very common, but possible).

The teletext specs also says, that a DVB teletext stream 
adaptation_field_control is either 01 or 10, which means that either there 
is an adaptation field or there is payload. Having both is NOT allowed.

If PCR needs to be transmitted, then it either has to be on a separate PCR 
PID or if you insist on using the same PID then you must use a separate 
packet with adaptation field only if you want to respect the 
specification.

>
>
>> The DVB teletext spec is very strict about that PES header size and 0x24
>> is hardcoded there.
>>
>> https://www.etsi.org/deliver/etsi_en/300400_300499/300472/01.03.01_60/en_300472v010301p.pdf
>
> Yes, you're right. The sentence at section "4.2 PES packet format" indicates:
>
> "PES_header_data_length set to "0x24"." And after it adds:
>
> "PTS and other optional fields may be present in the PES header,
> but the header length is always fixed for streams
> identified in the Program Specific Information (PSI) by the DVB Teletext descriptor"
>
> However, the idea of this restriction is to leave space for PTS data even if
> it's not present in the PES packet. And if you don't add any additional stuff
> in the TS header, the constraint is satisfied.
>
> Perhaps you'd prefer this behavior to be optional?

Our mpegts muxer should not generate streams which are not compliant with 
the relevant specifications. So the proper way to do what you want seems 
to be generating adaptation field only packets.

Regards,
Marton

Patch hide | download patch | download mbox

diff --git a/libavformat/mpegtsenc.c b/libavformat/mpegtsenc.c
index fc0ea22..f1772ac 100644
--- a/libavformat/mpegtsenc.c
+++ b/libavformat/mpegtsenc.c
@@ -1328,8 +1328,11 @@  static void mpegts_write_pes(AVFormatContext *s, AVStream *st,
                         header_len += 3;
             }
             if (is_dvb_teletext) {
-                pes_header_stuffing_bytes = 0x24 - header_len;
-                header_len = 0x24;
+                int header_stuff = (get_ts_payload_start(buf) - buf) - 4;
+                if (header_stuff - header_len > 0x24)
+                    header_stuff = 0;
+                pes_header_stuffing_bytes = 0x24 - header_len - header_stuff;
+                header_len = 0x24 - header_stuff;
             }
             len = payload_size + header_len + 3;
             /* 3 extra bytes should be added to DVB subtitle payload: 0x20 0x00 at the beginning and trailing 0xff */