save stream VP8 to webm file

[Trey Hutcheson]

I experience this exact same problem - though in my case the video is
coming via webrtcbin. It's been a defect on my backlog for a while now, but
I'm just now getting around to dealing with it. I've got some code put
together that works, but needs serious polish, but the sequence is:

* add a probe (EVENT_DOWNSTREAM) on the webmmux video sink pad to filter
for Caps events
* [if the pad has current caps] get the resolution from the current caps,
and the new caps, and compare
* If they differ (they will - that's the point here):
** unlink webmmux from its upstream element
** remove webmmux and filesink elements from container (a bin in my case,
not the root pipeline)
** set states of both elements to Null
** create new webmmux and filesink (to a new file) elements, link them, add
them to parent container
** set states to Playing
* repeat (add probe, etc)

A few notes about this approach:
* I had hoped that calling query_accept_caps on the pad with the new caps
would return false; but it doesn't. So I have to manually compare
resolutions
* I had hoped that unlinking the video sink pad and requesting a new video
sinking pad would work - effectively creating a new chapter in the target
file. Unfortunately that was not supported either.
* this approach creates N number of files for the source stream. My
requirements allow this; yours may not.

On Tue, Jun 30, 2020 at 2:17 PM <ogurin at auritek.com> wrote:

> Hello, I have a question.
>
>
>
> The task is to save VP8 from RTP packets into the webm file.
>
> There are all RTP packets already saved into the file.
>
> I am using pipeline like:
>
> appsrc block=true do-timestamp=true format=3 is-live=true
> name=video_appsrc  "
>
>                      "caps=\"application/x-rtp, media=(string)video,
> payload=(int)96, clock-rate=(int)90000,
> encoding-name=(string)VP8-DRAFT-IETF-01\" ! "
>
>                      "rtpvp8depay wait-for-keyframe=true ! webmmux
> name=mux ! filesink location=%s
>
>
>
> I assume that I get an error when resolution of the video changes into the
> stream:
>
>
>
> matroskamux matroska-mux.c:975:gst_matroska_mux_video_pad_setcaps:<mux>
> error: Caps changes are not supported by Matroska
>
> 0:00:00.371142012 26321       0xdcb8f0 INFO        GST_ERROR_SYSTEM
> gstelement.c:2224:gst_element_message_full_with_details:<mux> posting
> message: Could not multiplex stream.
>
> 0:00:00.371155378 26321       0xdcb8f0 INFO        GST_ERROR_SYSTEM
> gstelement.c:2251:gst_element_message_full_with_details:<mux> posted error
> message: Could not multiplex stream.
>
> 0:00:00.371169976 26321       0xdcb8f0 WARN             matroskamux
> matroska-mux.c:1356:gst_matroska_mux_video_pad_setcaps:<mux> pad video_0
> refused caps video/x-vp8, framerate=(fraction)0/1, height=(int)180,
> width=(int)320, profile=(string)0
>
>
>
> Please advise what I am doing wrong or maybe point me on error in pipeline
>
>
>
> Thank you in advance
>
>
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