Image encoding method and image encoding apparatus

1. An image encoding method for generating a bitstream having temporal scalability by encoding a plurality of images, comprising:

receiving an external parameter that specifies a bit rate type of the top temporal layer as being either a constant bit rate or a variable bit rate;

determining temporal layers having different temporal resolutions for each of a plurality of images;

setting, in a case where the constant bit rate is acquired, (1) a first bit rate type of a top temporal layer to the constant bit rate, and (2) a second bit rate type of one or more other layers to the variable bit rate;

setting, in a case where the variable bit rate is acquired, both the first bit rate type of the top temporal layer having the highest temporal resolution and the second bit rate type of the one or more layers having the lower temporal resolution to the variable bit rate;

encoding each of the plurality of images, prohibiting reference to the images with the temporal layers higher than each of the temporal layers that each of the images belongs to; and

generating the bitstream that includes temporal scalability information that indicates the temporal layers of the plurality of images, bit rate control information that indicates the first bit rate type and the second bit rate type, and the plurality of encoded images,

wherein the bitstream is input to a buffer, and

the input of at least one encoded image corresponding to the variable bit rate is interrupted when a free capacity of the buffer is lower than a threshold capacity.

2. The image encoding method according to claim 1 ,

wherein in the encoding, the plurality of images are encoded such that an image decoding apparatus performs processing on the bitstream in the first bit rate type without failure, by using a hypothetical reference decoder that hypothetically models buffer management of the image decoding apparatus.

3. The image encoding method according to claim 1 ,

wherein the temporal scalability information comprises a temporal identifier that indicates the temporal layers to which the plurality of images respectively belong, or a number of temporal resolutions that specify one or more of the temporal layers to be decoded.

4. An image encoding apparatus for generating a bitstream having temporal scalability by encoding a plurality of images, comprising:

a processor; and

a non-transitory memory having thereon a computer program, the computer program operable to cause the processor to execute operations, including

receiving an external parameter that specifies a bit rate type of the top temporal layer as being either a constant bit rate or a variable bit rate;

determining temporal layers having different temporal resolutions for each of a plurality of respective images;

setting, in a case where the constant bit rate is acquired, (1) a first bit rate type of a top temporal layer to the constant bit rate, and (2) a second bit rate type of one or more other layers to the variable rate;

setting, in a case where the variable bit rate is acquired, both the first bit rate type of the top temporal layer having the highest temporal resolution and the second bit rate type of the one or more layers having the lower temporal resolution to the variable bit rate;

encoding each of the plurality of images, prohibiting reference to the images with the temporal layers higher than each of the temporal layers that each of the images belongs to; and

generating the bitstream that includes temporal scalability information that indicates the temporal layers of the plurality of images, bit rate control information that indicates the first bit rate type and the second bit rate type, and the plurality of encoded images,

wherein the bitstream is input to a buffer, and

the input of at least one encoded image corresponding to the variable bit rate is interrupted when a free capacity of the buffer is lower than a threshold capacity.

5. A non-transitory computer-readable recording medium,

storing a program for causing a computer to execute the image encoding method according to claim 1 .

6. The image encoding method according to claim 1 ,

wherein the generating includes storing the generated bitstream to a buffer when an empty amount of the buffer is higher than a threshold capacity, and suspending the storing of the generated bitstream to the buffer when the empty amount of the buffer is lower than or equal to the threshold capacity.