Hi,
Stas Oskin wrote:
> Hi.
>
> I have a new issue where arbitrary live packets seems to be lost in
> transmission via DSS.
Sorry, I do not fully understand the problem... What's your setup?
Are you feeding a DSS with ffmpeg (over a local network) and then
accessing the DSS with a player via RTSP?
Or are you receiving video from DSS with ffmpeg and then restreaming
it?
According to your description, it looks like some packets are lost,
maybe because of network issues?
I mean, assuming that this is your setup:
|--------| ethernet |-----| ADSL
| ffmpeg |------------>| DSS |------------------> QT Player
|--------| |-----|
maybe some packets are lost on the ADSL because the instantaneous
bitrate of your stream is > 256kbps...
Even if the average bitrate is 256kbps, there can be some "peaks"
over 256kbps which can cause troubles (for example, if there are
some dark scenes without much motion the codec can use few bits
for them, resulting in a high bitrate for the following scenes).
If this is the problem, it can be solved by using rc_max_rate &
friends (but this will cause a degradation in the video quality).
You can use some tools like wireshark, tcpstats, and similar to
check what's happening in the network... Also, many players allow
to monitor the number of lost packets, the buffers' levels, etc...
Maybe you can use these statistics to understand where the problem
is.
> 1) When same packets are recorded to file, there are no garbage/jumps
> - the video is perfect.
>
> 2) When I re-stream the recorded video with ffmpeg command line, it
> also looks fine.
So, I assume that you are using your libav-based program to feed
a DSS, right? Are you saying that if you first encode some live video
to a file, and then you stream it in a second time, everything is fine?
If this is the case, then maybe you are seeing a different problem, due
to a drift between your computer's clock and the internal clock of the
video capture (or audio) card...
I expect this problem to appear after some hours of live streaming
(depending on the hardware quality, etc...).
The "ffmpeg" program provides a way to address this problem (-vsync
and -async). If you are usign your own program, you might need to
implement something similar.
> 3) I tried to connect directly to RTP port with VLC, it shows a lot of
> garbage (because of rtp?), and in case of live it plays only few
> frames and then stops. With recorded re-stream it plays it until the
> end.
How do you directly connect to the RTP port with VLC? Remember that
if you do not use an SDP description, things are not guaranteed to work.
> 4) The whole issue happens when the source is over remote ADSL
> (256Kbps) connection. When the source is in local LAN, there are no
> issues at all (the amount of frames per second is about the same - 15
> fps).
If you do not see problems when streaming on a local network, I guess
the stream's bitrate is to high for the ADSL (see the description at the
beginning of this email).
> 1) The FFMPEG RTP operates in UDP, hence some frames might be lost
> between DSS and LibAVCodec, causing the "garbage" and jumps. Any way
> to switch the RTP to TCP?
I dont' know if you are using ffmpeg as an RTSP client, or to feed
a DSS. In the first case, it should be possible to use RTP over RTSP
(I do not remember the exact option, but there should be one).
> 2) Could it be that the timing formula (with av_rescale_q) is somehow
> causing this?
In theory, no... But the network can introduce some jitter, causing
problems. You can correct the timing formula to send a small amount
of packets "in advance" to compensate for some possible network jitter.
You can also modify it to "smooth" the output bitrate, so that your
stream can be more "ADSL friendly".
> 3) Can someone recommend a good way to clearly playback video from
> live RTP, in order to pinpoint it on ffmpeg level and not on the DSS
> level? I tried ffplay but it didn't work.
Difficult to say without knowing your setup...
Also, can you describe a little bit more what didn't work?
Luca
_______________________________________________
libav-user mailing list
[email protected]
https://lists.mplayerhq.hu/mailman/listinfo/libav-user
