Last weekend, after few months of work, the new bitstream filter API eventually landed.<\/p>\n
In Libav is possible to manipulate raw and encoded data in many ways, the most common being<\/p>\n
Bitstream filtering is somehow less considered even if the are widely used under the hood to demux and mux many widely used formats.<\/p>\n
It could be consider an optional final demuxing or muxing step since it works on encoded data<\/strong> and its main purpose is to reformat the data so it can be accepted by decoders consuming only a specific serialization of the many supported (e.g. the HEVC<\/strong> QSV decoder) or it can be correctly muxed in a container<\/strong> format that stores only a specific kind.<\/p>\n In Libav this kind of reformatting happens normally automatically with the annoying exception of MPEGTS<\/strong> muxing.<\/p>\n The new API is modeled against the pull\/push paradigm<\/a> I described for AVCodec before<\/a>, it works on In order to use a bsf<\/strong> you need to:<\/p>\n You can enumerate<\/strong> the available filters<\/p>\n or directly pick the one you need by name<\/strong>:<\/p>\n A bsf<\/strong> may use some codec parameters<\/strong> and time_base<\/strong> and provide updated ones.<\/p>\n Multiple New API<\/h2>\n
AVPacket<\/code>s and has the following concrete implementation:<\/p>\n\/\/ Query<\/span>\nconst<\/span> AVBitStreamFilter<\/span> *<\/span>av_bsf_next<\/span>(<\/span>void<\/span> **<\/span>opaque<\/span>);<\/span>\nconst<\/span> AVBitStreamFilter<\/span> *<\/span>av_bsf_get_by_name<\/span>(<\/span>const<\/span> char<\/span> *<\/span>name<\/span>);<\/span>\n\n\/\/ Setup<\/span>\nint<\/span> av_bsf_alloc<\/span>(<\/span>const<\/span> AVBitStreamFilter<\/span> *<\/span>filter<\/span>,<\/span> AVBSFContext<\/span> **<\/span>ctx<\/span>);<\/span>\nint<\/span> av_bsf_init<\/span>(<\/span>AVBSFContext<\/span> *<\/span>ctx<\/span>);<\/span>\n\n\/\/ Usage<\/span>\nint<\/span> av_bsf_send_packet<\/span>(<\/span>AVBSFContext<\/span> *<\/span>ctx<\/span>,<\/span> AVPacket<\/span> *<\/span>pkt<\/span>);<\/span>\nint<\/span> av_bsf_receive_packet<\/span>(<\/span>AVBSFContext<\/span> *<\/span>ctx<\/span>,<\/span> AVPacket<\/span> *<\/span>pkt<\/span>);<\/span>\n\n\/\/ Cleanup<\/span>\nvoid<\/span> av_bsf_free<\/span>(<\/span>AVBSFContext<\/span> **<\/span>ctx<\/span>);<\/span>\n<\/pre>\n<\/div>\n\n
AVBitStreamFilter<\/code> using a query<\/strong> function.<\/li>\nAVBSFContext<\/code>, by allocating, configuring and then initializing it.<\/li>\nav_bsf_send_packet<\/code> function and get the processed output once it is ready using av_bsf_receive_packet<\/code>.<\/li>\nav_bsf_free<\/code> cleans up the memory used for the context and the internal buffers.<\/li>\n<\/ul>\nQuery<\/h3>\n
void<\/span> *<\/span>state<\/span> =<\/span> NULL<\/span>;<\/span>\n\nconst<\/span> AVBitStreamFilter<\/span> *<\/span>bsf<\/span>;<\/span>\n\nwhile<\/span> ((<\/span>bsf<\/span> =<\/span> av_bsf_next<\/span>(<\/span>&<\/span>state<\/span>))<\/span> {<\/span>\n av_log<\/span>(<\/span>NULL<\/span>,<\/span> AV_LOG_INFO<\/span>,<\/span> "%s<\/span>\\n<\/span>"<\/span>,<\/span> bsf<\/span>-><\/span>name<\/span>);<\/span>\n}<\/span>\n<\/pre>\n<\/div>\nconst<\/span> AVBitStreamFilter<\/span> *<\/span>bsf<\/span> =<\/span> av_bsf_get_by_name<\/span>(<\/span>"hevc_mp4toannexb"<\/span>);<\/span>\n<\/pre>\n<\/div>\nSetup<\/h3>\n
AVBSFContext<\/span> *<\/span>ctx<\/span>;<\/span>\n\nret<\/span> =<\/span> av_bsf_alloc<\/span>(<\/span>bsf<\/span>,<\/span> &<\/span>ctx<\/span>);<\/span>\nif<\/span> (<\/span>ret<\/span> <<\/span> 0<\/span>)<\/span>\n return<\/span> ret<\/span>;<\/span>\n\nret<\/span> =<\/span> avcodec_parameters_copy<\/span>(<\/span>ctx<\/span>-><\/span>par_in<\/span>,<\/span> in<\/span>-><\/span>codecpar<\/span>);<\/span>\nif<\/span> (<\/span>ret<\/span> <<\/span> 0<\/span>)<\/span>\n goto<\/span> fail<\/span>;<\/span>\n\nctx<\/span>-><\/span>time_base_in<\/span> =<\/span> in<\/span>-><\/span>time_base<\/span>;<\/span>\n\nret<\/span> =<\/span> av_bsf_init<\/span>(<\/span>ctx<\/span>);<\/span>\nif<\/span> (<\/span>ret<\/span> <<\/span> 0<\/span>)<\/span>\n goto<\/span> fail<\/span>;<\/span>\n\nret<\/span> =<\/span> avcodec_parameters_copy<\/span>(<\/span>out<\/span>-><\/span>codecpar<\/span>,<\/span> ctx<\/span>-><\/span>par_out<\/span>);<\/span>\nif<\/span> (<\/span>ret<\/span> <<\/span> 0<\/span>)<\/span>\n goto<\/span> fail<\/span>;<\/span>\n\nout<\/span>-><\/span>time_base<\/span> =<\/span> ctx<\/span>-><\/span>time_base_out<\/span>;<\/span>\n<\/pre>\n<\/div>\nUsage<\/h3>\n
AVPackets<\/code> may be consumed before an AVPacket<\/code> is emitted or multiple