Abstract: A TV receiver is adapted to display either the regularly broadcast video signals or videotext information. The video signals contain their own internal synchronization signals. The videotext information requires locally generated synchronization signals which may be used to replace the normal video internal synchronization signals. The invention provides means for switching between the normally broadcast and the internally generated synchronization signals.

Abstract: A numerical or digital transmission system uses an adaptative coding, of log information, which is sampled and transformed by an orthogonal transformation. The coding has a rate of data flow or delivery, which is reduced by orthogonal transformation with an adaptative threshold. In each scanning field, the binary elements of the coefficients are obtained by a basic coding with a quantification pitch 2S, (S being a whole number either positive or null). A complementary coding is transmitted. The complementary coding is obtained by adding binary elements of weights 2S-1 for each one of the coefficients, until the transmission capacity of the channel is filled. The coefficients are taken in chronological order. The invention is applicable to digital television, but also the coding may be used for transmission of high fidelity sound.