[vlc-devel] [PATCH 1/1] udp: support packets dump in access_out module

Tzu-Jung Lee roylee17 at gmail.com
Thu Jul 11 14:32:08 CEST 2013

Hi Rafael,

Please let me elaborate the situation I have, which is the motivation
to have the dumps for access and accees_out modules.

I'm working on a transcoding device which takes TS over UDP, transcode
them, and streams out TS over UDP.

    ts/udp -> device -> ts/udp

Before implementing something like the vdpau, I'm trying to use two
VLC instances to do the job for now.
(I implemented a preliminary v4l2 output module, modified from the
v4l2 access module)

The two VLC instances on the device:

   a) cvlc udp:// --sout #'std{access=v4l2c,mux=ts}' &
   b) cvlc v4l2c:// --sout #'std{access=udp,dst=}' &

To test this, we also runs two VLC instances on a PC, one feed the
source stream while the other displays the transcoded result.

   c) cvlc feed.ts --sout #std{access=udp,dst=}' &
   d) vlc udp://

Currently the final display looks very blocky, and sometimes even broken.
Our video folks insist that VLC did something to the clip so the
device can't transcode it correctly.
And I also did a experiment on PC:

   e) cvlc feed.ts --sout #std{access=udp,dst=}' &
   f)  udp:// --sout #std{access=file,dst=saved.ts}' &

It turns out the saved.ts already has obvious artifices.
I notice that muxer/demuxer/udp all discard data if it think it have
some problems such as strange time-stamps.

So I'm going to add the dumps at several point in the following
pipeline to find out at which stages the clips is still okay for our

    file_access ->demux -> mux-> udp_out   /  udp_access -> demux ->
mux -> v4l2_out -> device -> v4l2_access -> demux -> mux -> udp_out

With these feature, the intermediate dumps can be recorded for the
existing VLC-only setup without external tools.

Hope the folks on the list also find it useful in other circumstances.



On Thu, Jul 11, 2013 at 7:32 PM, Rafaël Carré <funman at videolan.org> wrote:
> Hi,
> Le 11/07/2013 13:10, Tzu-Jung Lee a écrit :
>> Signed-off-by: Tzu-Jung Lee <tjlee at ambarella.com>
>> ---
>>  modules/access_output/udp.c | 28 ++++++++++++++++++++++++++++
>>  1 file changed, 28 insertions(+)
> For access_output, I send to a multicast address and then dump it with
> netcat or another VLC.
> Thus I think this patch is nice but not necessary as other solutions exist.
> What do you think?
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