Well.... now that I've gone to read the code again, you're absolutely right that I was too hasty in calling it the "byte-by-byte" state. It's more like the "sli

Well.... now that I've gone to read the code again, you're absolutely right that I was too hasty in calling it the "byte-by-byte" state. It's more like the "slice-by-slice" state. libmpeg2 goes header-by-header, so, it can process each individual slice without waiting for the next picture start code, but it does buffer up a whole slice before starting any work. If you just give it a single byte (or any number of bytes that doesn't include some subsequent start code, including a sequence_end_code for the end of the whole video), it just copies it to an internal buffer and then asks for more until it sees the beginning of the next slice or some other header. That's why NEEDBITS and DUMPBITS don't have to bail out in the middle -- by the time you get there, you know they have a whole slice to play with. So, yes, libmpeg2 does go start-code (or sequence_end_code) by start-code -- but not a picture start code. ffmpeg/libavcodec is a wrapper around like 75+ different decoders, so I'm not too surprised if they have to go with a least-common-denominator interface. In general an MPEG-2 TS or PS packet is just a fixed size packet and doesn't have to be aligned with any ES syntax element. Typically the PES packets (the much larger packets encapsulated in PS/TS packets) do contain exactly one video picture (i.e. the data_alignment_indicator is set on every video PES packet), but even this isn't formally required. Note that the PES packet header also includes an optional length field that would do what you want (but it's optional, in part to accommodate encoders that don't want to buffer the whole image before starting to encode pixels). You might be interested in our TS/PES demuxing code that wraps libmpeg2/liba52 and tries to maintain a/v sync in the presence of arbitrary corruption -- it's more than half the size of your entire decoder! https://github.com/StanfordSNR/puffer/blob/master/src/atsc/decoder.cc https://github.com/StanfordSNR/puffer/blob/master/src/atsc/d...