mpeg-ts fundamental

Question

I read some tutorials about mpeg transport stream, but there are 2 fundamental issues I do not understand: 1. mpeg-ts muxer recieve pes packets from audio and video, and output mpeg-ts packets. How does it do this muxing ? Is it that whenever a packet from any program is waiting on its input, that the muxer wakes up and process the pes slicing into mpeg-ts ? 2. Is it that the user can select which bit rate the mpeg-ts muxer will output ? what is the connection between the rate of the encoding to the rate of mpeg-ts ?

Thank you very much,

Ran

Answer 1

MPEG2-TS muxing is a complex art-form. Suggested reading: MPEG2-TS specification, SPTS/MPTS, VBR vs. CBR, Hypothetical reference decoder and buffers (EB, MB, TB), jitter and drift.

a very short answer to your questions can be summarized like this: for each encoder, on the other end of the line there is a decoder which wants to display a video frame (or audio frame) every frame interval. this frame needs to be decoded before its presentation time. if this frame uses other frames as reference, they also need to be decoded prior to presentation. when multiplexing, the data must arrive sufficient time before presentation. A video frame to be presented at time n must be available at decoder at time n - x where is x is a measure of time depending on the buffer rate of the decoder (see MB,TB,EB). if TS bit rate is too low, "underflow" occurs and the video is not in the decoder on time. if TS bit rate is too large, "overflow" occurs, and the buffers have to drop packets which will also create visual artifacts.