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I know by testing that my Samsung D will play .flv container files (video/x-flv) containing h264(avc) video and aac audio streams.

According to the Transcoding Config document, this entry in the Samsung 7 Profile will transcode any flv with an h264(avc) codec regardless of the audio to an mpegts with a copied h264 video and a converted ac3 audio.

<Video targetContainer="mpegts" targetACodec="ac3">
<Matches container="flv" vCodec="h264" />

When I play one of these videos using this rule, the mime displays as video/mpeg and the skip forward/back is disabled.

To work around this I first tried

<Video targetContainer="mpeg" targetACodec="ac3">
<Matches container="flv" vCodec="h264" />
then
<Video targetContainer="asf" targetACodec="ac3">
<Matches container="flv" vCodec="h264" />

Both of these are valid Samsung file formats but DLNA gave me "unsupported file format" errors.

Is Mpegts the only container I can transcode to?

you have to provide targetVCodec="mpeg2video" for the mpeg case, mpegPS only allows mpeg2 video stream, not h264. Obviously more CPU will be used in this case.