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Bufferless (on the fly) video data generation for the video device class #3322

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032de0b
Video Class: New callback function added which allows to generate fra…
Oct 30, 2025
b8cea4a
Added bufferless operation to the video capture example. Can be teste…
Oct 30, 2025
889cde7
Video class: Changed pararameters of payload request to a dedicated s…
Oct 30, 2025
6b3970d
Fixed trailing whitespaces in files (used wrong editor)
Oct 31, 2025
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69 changes: 54 additions & 15 deletions examples/device/video_capture/src/main.c
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Original file line number Diff line number Diff line change
Expand Up @@ -56,6 +56,20 @@ void video_task(void* param);
void freertos_init_task(void);
#endif

#if !defined(CFG_EXAMPLE_VIDEO_READONLY) || defined(CFG_EXAMPLE_VIDEO_BUFFERLESS)
/* EBU color bars: https://stackoverflow.com/questions/6939422 */
static uint8_t const bar_color[8][4] = {
/* Y, U, Y, V */
{ 235, 128, 235, 128}, /* 100% White */
{ 219, 16, 219, 138}, /* Yellow */
{ 188, 154, 188, 16}, /* Cyan */
{ 173, 42, 173, 26}, /* Green */
{ 78, 214, 78, 230}, /* Magenta */
{ 63, 102, 63, 240}, /* Red */
{ 32, 240, 32, 118}, /* Blue */
{ 16, 128, 16, 128}, /* Black */
};
#endif

//--------------------------------------------------------------------+
// Main
Expand Down Expand Up @@ -111,12 +125,43 @@ void tud_resume_cb(void) {
blink_interval_ms = tud_mounted() ? BLINK_MOUNTED : BLINK_NOT_MOUNTED;
}

#ifdef CFG_EXAMPLE_VIDEO_BUFFERLESS

#ifndef CFG_EXAMPLE_VIDEO_DISABLE_MJPEG
#error Demo only supports YUV2 please define CFG_EXAMPLE_VIDEO_DISABLE_MJPEG
#endif

void tud_video_prepare_payload_cb(uint_fast8_t ctl_idx, uint_fast8_t stm_idx, tud_video_payload_request_t* request)
{
static uint32_t frame_counter = 0;
(void)ctl_idx;
(void)stm_idx;

/* Offset will be zero at the start of a new frame */
if (!request->offset) frame_counter++;

for (size_t buf_pos = 0; buf_pos < request->length; buf_pos += 2) {

/* Position within the current line (pixel relative) */
int line_pos = ((request->offset + buf_pos)>>1) % FRAME_WIDTH;

/* Choose color based on the position and change the table offset every 4 frames */
const uint8_t* color = bar_color[(line_pos/(FRAME_WIDTH / 8) + (frame_counter>>2)) % 8];

/* Copy pixel data for odd or even pixels */
memcpy(&((uint8_t*)request->buf)[buf_pos], &color[(line_pos & 1) ? 2 : 0], 2);
}

}
#endif

//--------------------------------------------------------------------+
// USB Video
//--------------------------------------------------------------------+
static unsigned frame_num = 0;
static unsigned tx_busy = 0;
static unsigned interval_ms = 1000 / FRAME_RATE;
#ifndef CFG_EXAMPLE_VIDEO_BUFFERLESS

#ifdef CFG_EXAMPLE_VIDEO_READONLY
// For mcus that does not have enough SRAM for frame buffer, we use fixed frame data.
Expand Down Expand Up @@ -145,18 +190,6 @@ static struct {
static uint8_t frame_buffer[FRAME_WIDTH * FRAME_HEIGHT * 16 / 8];

static void fill_color_bar(uint8_t* buffer, unsigned start_position) {
/* EBU color bars: https://stackoverflow.com/questions/6939422 */
static uint8_t const bar_color[8][4] = {
/* Y, U, Y, V */
{ 235, 128, 235, 128}, /* 100% White */
{ 219, 16, 219, 138}, /* Yellow */
{ 188, 154, 188, 16}, /* Cyan */
{ 173, 42, 173, 26}, /* Green */
{ 78, 214, 78, 230}, /* Magenta */
{ 63, 102, 63, 240}, /* Red */
{ 32, 240, 32, 118}, /* Blue */
{ 16, 128, 16, 128}, /* Black */
};
uint8_t* p;

/* Generate the 1st line */
Expand All @@ -183,6 +216,8 @@ static void fill_color_bar(uint8_t* buffer, unsigned start_position) {

#endif

#endif /* NDEF CFG_EXAMPLE_VIDEO_BUFFERLESS */

static void video_send_frame(void) {
static unsigned start_ms = 0;
static unsigned already_sent = 0;
Expand All @@ -197,7 +232,9 @@ static void video_send_frame(void) {
already_sent = 1;
tx_busy = 1;
start_ms = board_millis();
#ifdef CFG_EXAMPLE_VIDEO_READONLY
#if defined(CFG_EXAMPLE_VIDEO_BUFFERLESS)
tud_video_n_frame_xfer(0, 0, NULL, FRAME_WIDTH * FRAME_HEIGHT * 16 / 8);
#elif defined (CFG_EXAMPLE_VIDEO_READONLY)
#if defined(CFG_EXAMPLE_VIDEO_DISABLE_MJPEG)
tud_video_n_frame_xfer(0, 0, (void*)(uintptr_t)&frame_buffer[(frame_num % (FRAME_WIDTH / 2)) * 4],
FRAME_WIDTH * FRAME_HEIGHT * 16/8);
Expand All @@ -216,13 +253,15 @@ static void video_send_frame(void) {
start_ms += interval_ms;
tx_busy = 1;

#ifdef CFG_EXAMPLE_VIDEO_READONLY
#if defined(CFG_EXAMPLE_VIDEO_BUFFERLESS)
tud_video_n_frame_xfer(0, 0, NULL, FRAME_WIDTH * FRAME_HEIGHT * 16 / 8);
#elif defined(CFG_EXAMPLE_VIDEO_READONLY)
#if defined(CFG_EXAMPLE_VIDEO_DISABLE_MJPEG)
tud_video_n_frame_xfer(0, 0, (void*)(uintptr_t)&frame_buffer[(frame_num % (FRAME_WIDTH / 2)) * 4],
FRAME_WIDTH * FRAME_HEIGHT * 16/8);
#else
tud_video_n_frame_xfer(0, 0, (void*)(uintptr_t)frames[frame_num % 8].buffer, frames[frame_num % 8].size);
#endif
#endif
#else
fill_color_bar(frame_buffer, frame_num);
tud_video_n_frame_xfer(0, 0, (void*) frame_buffer, FRAME_WIDTH * FRAME_HEIGHT * 16 / 8);
Expand Down
1 change: 1 addition & 0 deletions examples/device/video_capture/src/tusb_config.h
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Original file line number Diff line number Diff line change
Expand Up @@ -110,6 +110,7 @@

//#define CFG_EXAMPLE_VIDEO_READONLY
//#define CFG_EXAMPLE_VIDEO_DISABLE_MJPEG
//#define CFG_EXAMPLE_VIDEO_BUFFERLESS

#ifdef __cplusplus
}
Expand Down
21 changes: 18 additions & 3 deletions src/class/video/video_device.c
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Original file line number Diff line number Diff line change
Expand Up @@ -214,6 +214,12 @@ TU_ATTR_WEAK int tud_video_commit_cb(uint_fast8_t ctl_idx, uint_fast8_t stm_idx,
return VIDEO_ERROR_NONE;
}

TU_ATTR_WEAK void tud_video_prepare_payload_cb(uint_fast8_t ctl_idx, uint_fast8_t stm_idx, tud_video_payload_request_t* request) {
(void) ctl_idx;
(void) stm_idx;
(void) request;
}

//--------------------------------------------------------------------+
//
//--------------------------------------------------------------------+
Expand Down Expand Up @@ -860,7 +866,16 @@ static uint_fast16_t _prepare_in_payload(videod_streaming_interface_t *stm, uint
}
TU_ASSERT(pkt_len >= hdr_len);
uint_fast16_t data_len = pkt_len - hdr_len;
memcpy(&ep_buf[hdr_len], stm->buffer + stm->offset, data_len);
if (stm->buffer) {
memcpy(&ep_buf[hdr_len], stm->buffer + stm->offset, data_len);
} else {
tud_video_payload_request_t rqst = {
.buf = &ep_buf[hdr_len],
.length = data_len,
.offset = stm->offset
};
tud_video_prepare_payload_cb(stm->index_vc, stm->index_vs, &rqst);
}
stm->offset += data_len;
remaining -= data_len;
if (!remaining) {
Expand Down Expand Up @@ -1235,11 +1250,11 @@ bool tud_video_n_frame_xfer(uint_fast8_t ctl_idx, uint_fast8_t stm_idx, void *bu
TU_ASSERT(ctl_idx < CFG_TUD_VIDEO);
TU_ASSERT(stm_idx < CFG_TUD_VIDEO_STREAMING);

if (!buffer || !bufsize) return false;
if (!bufsize) return false;
videod_streaming_interface_t *stm = _get_instance_streaming(ctl_idx, stm_idx);
videod_streaming_epbuf_t *stm_epbuf = &_videod_streaming_epbuf[ctl_idx];

if (!stm || !stm->desc.ep[0] || stm->buffer) return false;
if (!stm || !stm->desc.ep[0] || stm->bufsize) return false;
if (stm->state == VS_STATE_PROBING) return false;

/* Find EP address */
Expand Down
20 changes: 20 additions & 0 deletions src/class/video/video_device.h
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Original file line number Diff line number Diff line change
Expand Up @@ -35,6 +35,16 @@
extern "C" {
#endif


//--------------------------------------------------------------------+
// Payload request
//--------------------------------------------------------------------+
typedef struct TU_ATTR_PACKED {
void* buf; /* Payload buffer to be filled */
size_t length; /* Length of the requested data in bytes */
size_t offset; /* Offset within the frame (in bytes) */
} tud_video_payload_request_t;

//--------------------------------------------------------------------+
// Application API (Multiple Ports)
// CFG_TUD_VIDEO > 1
Expand Down Expand Up @@ -83,6 +93,16 @@ int tud_video_power_mode_cb(uint_fast8_t ctl_idx, uint8_t power_mod);
int tud_video_commit_cb(uint_fast8_t ctl_idx, uint_fast8_t stm_idx,
video_probe_and_commit_control_t const *parameters);

/** Invoked if buffer is set to NULL (allows bufferless on the fly data generation)
*
* @param[in] ctl_idx Destination control interface index
* @param[in] stm_idx Destination streaming interface index
* @param[out] payload_buf Payload storage buffer (target buffer for requested data)
* @param[in] payload_size Size of payload_buf (requested data size)
* @param[in] offset Current byte offset relative to given bufsize from tud_video_n_frame_xfer (framesize)
* @return video_error_code_t */
void tud_video_prepare_payload_cb(uint_fast8_t ctl_idx, uint_fast8_t stm_idx, tud_video_payload_request_t* request);

//--------------------------------------------------------------------+
// INTERNAL USBD-CLASS DRIVER API
//--------------------------------------------------------------------+
Expand Down
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