AW: single frame snapshot

[Thornton, Keith]

Hi, I do this by setting a pad probe at the start of the pipeline and only letting one frame through. I wait for the frame tob e an IDR frame bevor letting it through. Something similar to the logic below

pThumbnail->letBufferThrough();
gst_pad_add_probe(m_pFirstElementSinkPad, GST_PAD_PROBE_TYPE_BUFFER, static_cast<GstPadProbeCallback>(cb_blocked), pThumbnail, 0);

static GstPadProbeReturn cb_blocked(GstPad* pad, GstPadProbeInfo* info, gpointer user_data)
    {
        Q_UNUSED(info);
        Q_UNUSED(pad);
        GstreamerH264Thumbnail* pThumbnail = static_cast<GstreamerH264Thumbnail*>(user_data);
        if (pThumbnail->isLetBufferThrough())
        {
			GstBuffer * pBuffer = gst_pad_probe_info_get_buffer(info);
			if (pBuffer) {
				if (GST_BUFFER_FLAG_IS_SET(pBuffer, GST_BUFFER_FLAG_DELTA_UNIT)) {
					return GST_PAD_PROBE_DROP;
				}
			}
			return GST_PAD_PROBE_PASS;
		}
        else
        {
            return GST_PAD_PROBE_DROP;
        }
    }




-----Ursprüngliche Nachricht-----
Von: gstreamer-devel [mailto:gstreamer-devel-bounces at lists.freedesktop.org] Im Auftrag von jmz
Gesendet: Freitag, 14. Juli 2017 08:46
An: gstreamer-devel at lists.freedesktop.org
Betreff: single frame snapshot

I want to take a snapshot of one single frame from H.264 stream. I have tried several pipelines but they did not work.

1. I used "pngenc snapshot=true ! filesink" as follows:
... ! h264parse ! avdec_h264 ! videoconvert ! pngenc snapshot=true !
filesink location=sink.png

Although one sink.png file was generated, several PNG images, in fact, are stored in this file (see the finding in my next pipeline).

2. I replaced filesink with multifilesink as follows:
... ! h264parse ! avdec_h264 ! videoconvert ! pngenc snapshot=true !
multifilesink location=img%d.png

Three files img1.png ~ img3.png were generated. I found that the total size of the three files is equal to the size of the previous sink.png. Why doesn't "snapshot=true" (Send EOS after encoding a frame) work with pngenc?

3. I added "next-file=key-frame" to multifilesink as follows:

... ! h264parse ! avdec_h264 ! videoconvert ! pngenc snapshot=true !
multifilesink location=key%d.png next-file=key-frame

Only one key1.png was generated. But the file size is equal to the sink.png (also the sum of img1.png ~ img3.png). Should "next-file=key-frame" generate new file at only keyframe?

Can I use jpegenc to take one single JPEG snapshot of H.264 stream?




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