MJPEG Stream Information

Question

I am receiving a MJPEG Stream from my camera. When I look at the video data with an hex editor it seems that it doesn't contain any streaming information. I just see one raw JPEG after another, but no information about the framerate etc. .

Is the lack of any meta information normal for MJPEG or is it just related to the camera I am using? If there a no information about the stream, how can a player know how fast to play the video?

Answer 1

The lack of metadata is normal. IP Cameras typically send MJPEG as just that, one JPEG image after another as a stream. This is the most basic valid MJPEG file. If you were to take a bunch of jpegs, cat them together into a large, giant file, and feed it to ffmpeg, it would see it as a valid mjpeg format file. Some cameras will add an additional header to contain audio data, but it is not needed to be considered valid motion jpeg.

Many cameras will include a header like X-Framerate, in the HTTP header when the stream is initially sent, or you can set it as part of the camera configuration. However, when a camera sends only jpegs, there is no way to tell from the stream itself what the framerate is.

Answer 2

Is the lack of any meta information normal for MJPEG or is it just related to the camera I am using? If there a no information about the stream, how can a player know how fast to play the video?

To add to already answered, IP camera is a live video source and frames are typically presented as soon as they arrive from camera. Rare IP camera attaches extra per frame information other than fame size (some don't do even this! they send data and separators only). Still some do attach time stamps and extra data like motion detection state.

Most of the IP cameras don't do constant frame rate. That is, frame rate might vary, esp. lower down in low light conditions. It is the responsibility of the receiving side to attach per frame time stamps when multiplexing the data into container format. Time stamp might be recovered from metadata (which rarely exists) or - more frequently - receiver stamps a frame with local receive time.

This is the way for the player to play back video sequence in proper rate. Live feed is typically presented on "show received frame as soon as possible" basis.