Microsoft Answers Your Questions About Encoding, Codecs and Silverlight

Microsoft_Expression_Encoder_4 recently hosted a webinar entitled "Encoding Workshop: Best Practices and Strategies" and attendees had quite a few questions about Silverlight, SmoothStreaming and other Microsoft technologies. So Allan Poore, Principal Group Manager for Expression Encoder at Microsoft nicely answered some of the most common questions below. You can also view the webinar on-demand and if you have additional questions about Expression Encoder, you can email Microsoft for answers.

Question: What are pros and cons of using H.264 and VC1 for Silverlight Smooth Streaming? Why would you select one over other?

Answer: Smooth Streaming's VC-1 implementation can support 2-pass VBR, adaptive GOP length, and dynamic frame resizing. The H.264 implementation is like the old VC-1 CBR Smooth Encoder, with a fixed GOP length and 1-pass CBR only. In general, VC-1 will have better results for Windows and Macintosh playback, particularly when CPU performance is a bigger limitation than bandwidth.

Question: Should I deinterlace 1080i and downscale to 720p with an external hardware scaler, or should I put 1080i straight into the Expression Encoder for a 432 x 768 output size?

Answer: I would recommend bringing this straight into the Expression Encoder. We often do a better job scaling and resizing than many hardware converters.

Question: How does H.264 compression compare to Windows Media/VC1 in video quality at encoding rates below 1mbps?

Answer: VC-1 is pretty competitive with H.264 Baseline in terms of quality. H.264 High Profile provides better quality at low bitrates, but has higher requirements to decode in software. So, if a device supports both VC-1 and H.264 High Profile in hardware, H.264 High is probably the best bet. When decoding in software (like Silverlight) the speed of the decode can be a bigger limitation than bitrate. So in these cases VC-1 can often provide a better overall experience.

Question: For high camera motion video such as a stabilizer or rolling dolly, what is the best approach to prevent artifacts in encoding? Is it best to increase bitrate or keyframe intervals?

Answer: The best way to preserve quality with high motion content is to increase the bitrate and/or reduce the frame size. Increasing keyframe intervals will likely not make much of a difference.

Question: Is it possible to do live transcoding and apply standard DRM for encryption at the same time?

Answer: Yes, this is possible today in Expression Encoder v4 on Smooth Streaming output. In the output tab there are Digital Rights Management settings that allow you to specify a PlayReady server that will encrypt your live content as it is being broadcast.  

Question: How is SVC encoding different than Adaptive Streaming?

Answer: The Scale Video Codec (SVC) contains subset bitstreams that build upon each other to enhance resolution, frame rate and quality. You can think of it in terms of layers that are added on to each other to create a high-quality video.  Adaptive Bitrate Streaming (e.g. <> IIS Smooth Streaming) uses separate video files or streams that have different bitrates, resolutions, frame rates, etc.  The client communicates with the server to tell it which type of stream it can playback at any given time. This is dynamic because if the network conditions change for the worse, the client can request a small sized stream to avoid stuttering playback or buffering.  

Question: What is the recommended HD capture card for Expression Encoder?

Answer: We work with a variety of capture card vendors, including Black Magic, Viewcast, and Winnov.  You can find the full Expression Encoder Pro 4 system requirements here.

Question: Is there a time limit that the basic Expression Encoder in Windows 7 will run before stopping encoding?

Answer: We offer two versions of Expression Encoder.   Expression Encoder 4 is a free VC-1 encoding and video-editing application with up to 10 minutes of screen capture. Expression Encoder Pro adds H.264 encoding (both MP4 and Smooth Streaming), Live Smooth Streaming encoding, DRM, native support of MP4/H.264, TS, M2TS, AVCHD, MPEG-2, ISM, ISMV, AAC and AC-3 files, and unlimited screen capture durations.