LEAD AAC Transcoder

The LEAD AAC Transcoder is a DirectShow filter. It is used to transcode AAC audio stream in mpeg2 format to ACC in ISO (mpeg4) format or vice versa. This filter changes AAC packets format without performing re-compression of the audio stream or the data packets. Converting with this filter is fast, while the quality of the original stream is preserved. To convert without re-compression, an AAC stream inside a MPEG2 transport file to ISO format, or vice versa, LEAD AAC Transcoder filter should be inserted between mpeg2 demux and ISO multiplexer. LEAD Multimedia toolkit automatically inserts the filter in this manner.

Filter Interfaces	N/A
Interface ID	N/A
Input Media Types	Type: MEDIATYPE_Audio Subtypes: MEDIASUBTYPE_AAC MEDIASUBTYPE_mp4a
Output Media Types	Type: MEDIATYPE_Audio Subtype: MEDIASUBTYPE_mp4a MEDIASUBTYPE_AAC
Filter CLSID	CLSID_LMAACTranscoder
Filter category	CLSID_AudioCompressorCategory
Executable	LTranscoderAAC.dll, DSKernel2.dll

Platforms

Win32, x64

To illustrate the advantage of using transcoders, two setups are provided below for comparison. Observe (Figure 1) how the transcoders are positioned between LEAD MPEG Transport Demultiplexer and LEAD ISO Multiplexer. Now observe the next image (Figure 2) and how in between the same LEAD MPEG2 Transport Demultiplexer and LEAD ISO Multiplexer there is a need to use encoders and decoders. As a result of using decoding-encoding filters, the processing of data is slower than the speeds attained with data re-packetizing - a key feature of transcoders.

Figure 1. Re-packetizing of Data Using Transcoders.