CODEWITHSUNDEEP
c++ffmpeggstreamerh.264directshow
rafauu
rafauu

Reputation: 101

Is stream-format in h264 related to camera provided stream or is it more like transport thing?

I've got camera that produces video stream in different formats. One of them is h264 encoded stream. I use dshow along with gstreamer to acquire this stream and process it with c++ and send it also via shared memory. My question is related specifically to field stream-format in gst caps. How do I know whether it is byte-stream or avc? Is it tightly coupled to stream produced by camera or is it like transport thing that I set with gstreamer by my own? I work with rather complicated commercial specific pipelines that I cannot share full here. When I set in my code gst_caps_set_simple (gstCaps, "stream-format", G_TYPE_STRING, "byte-stream", nullptr); it works but I am not 100% why so I want to clarify that.

I've tried checking information about this specific camera with ffmpeg but I cannot get info about stream-format. Best I got is: ffmpeg -f dshow -list_options true -i video="nameOfCamera"

(...)
vcodec=h264  min s=128x96 fps=0.015625 max s=768x480 fps=29.97
vcodec=h264  min s=128x96 fps=0.015625 max s=768x576 fps=25
vcodec=h264  min s=128x96 fps=0.015625 max s=768x480 fps=29.97
vcodec=h264  min s=128x96 fps=0.015625 max s=768x576 fps=25
vcodec=h264  min s=128x96 fps=0.015625 max s=768x480 fps=29.97
vcodec=h264  min s=128x96 fps=0.015625 max s=768x576 fps=25
vcodec=h264  min s=128x96 fps=0.015625 max s=768x576 fps=25
(...)

Upvotes: 1

Views: 218

Answers (1)

Florian Zwoch
Florian Zwoch

Reputation: 7373

I would think the interface from how you get the data from should specify the data format.

byte-stream in GStreamer terms is the regular H.264 byte-stream as per H.264 specification with start codes, start code emulation bytes etc.

Alternatively avc samples can be an alternative format (MP4 files store H.264 data as AVC samples, and not byte-stream). AVC samples are basically [nal length][nal data of length size]... chunks (no start codes or start code emulation bytes).

AVC samples give you quick NAL chunk access, for the regular byte-stream would have to do a bit more parsing.

So you will have to set the type whatever you get into GStreamer so the downstream element knows what type of data to expect.

Upvotes: 2

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