Re: [FFmpeg-devel] [PATCH] avcodec: add Radiance HDR image format support

[James Almer <jamrial@gmail.com>]

On 7/6/2022 4:09 PM, Andreas Rheinhardt wrote:
> James Almer:
>> On 7/6/2022 3:47 PM, Paul B Mahol wrote:
>>> Added parser.
>>> The test will be added after this is merged.
>>
>> [...]
>>
>>> +static int hdr_parse(AVCodecParserContext *s, AVCodecContext *avctx,
>>> +                     const uint8_t **poutbuf, int *poutbuf_size,
>>> +                     const uint8_t *buf, int buf_size)
>>> +{
>>> +    HDRParseContext *ipc = s->priv_data;
>>> +    uint64_t state = ipc->pc.state64;
>>> +    int next = END_NOT_FOUND, i = 0;
>>> +
>>> +    s->pict_type = AV_PICTURE_TYPE_NONE;
>>
>> pict_type I, and key frame?
>>
>> [...]
>>
>>> +static int hdr_encode_frame(AVCodecContext *avctx, AVPacket *pkt,
>>> +                            const AVFrame *frame, int *got_packet)
>>> +{
>>> +    HDREncContext *s = avctx->priv_data;
>>> +    int64_t packet_size;
>>> +    uint8_t *buf;
>>> +    int ret;
>>> +
>>> +    packet_size = avctx->width * avctx->height * 4LL + 1024LL;
>>> +    if ((ret = ff_get_encode_buffer(avctx, pkt, packet_size, 0)) < 0)
>>
>> Wont using worst case scenario like this result in massive packets?
>> av_shrink_packet() only changes the size field, it doesn't realloc the
>> buffer to shrink it.
>>
>> You could allocate a buffer in HDREncContext with
>> av_fast_padded_malloc() here, use the bytestream2 API below, then
>> allocate the packet with ff_get_encode_buffer() using
>> bytestream2_tell_p() as size and do a memcpy at the end.
>>
> 
> If that is the aim, then there is no reason to do the memcpy ourselves
> (or do the av_fast_padded_malloc directly): Just use ff_alloc_packet()
> and the generic code will ensure that the packet data will be made
> refcounted. And the temp buffer will be freed generically, too.

The idea is to keep the encoder working with user provided buffers, 
while not allocating worst case scenario packets.

> 
>>> +        return ret;
>>> +
>>> +    buf = pkt->data;
>>> +    bytestream_put_str(&buf, "#?RADIANCE\n");
>>> +    bytestream_put_str(&buf, "SOFTWARE=lavc\n");
>>> +    ret = snprintf(buf, 32, "PIXASPECT=%f\n",
>>> av_q2d(av_inv_q(avctx->sample_aspect_ratio)));
>>> +    if (ret > 0)
>>> +        buf += ret;
>>> +    bytestream_put_str(&buf, "FORMAT=32-bit_rle_rgbe\n\n");
>>> +    ret = snprintf(buf, 32, "-Y %d +X %d\n", avctx->height,
>>> avctx->width);
>>> +    if (ret > 0)
>>> +        buf += ret;
>>> +
>>> +    for (int y = 0; y < avctx->height; y++) {
>>> +        const float *red   = (const float *)(frame->data[2] + y *
>>> frame->linesize[2]);
>>> +        const float *green = (const float *)(frame->data[0] + y *
>>> frame->linesize[0]);
>>> +        const float *blue  = (const float *)(frame->data[1] + y *
>>> frame->linesize[1]);
>>> +
>>> +        if (avctx->width < 8 || avctx->width > 0x7fff) {
>>> +            for (int x = 0; x < avctx->width; x++) {
>>> +                float2rgbe(buf, red[x], green[x], blue[x]);
>>> +                buf += 4;
>>> +            }
>>> +        } else {
>>> +            bytestream_put_byte(&buf, 2);
>>> +            bytestream_put_byte(&buf, 2);
>>> +            bytestream_put_byte(&buf, avctx->width >> 8);
>>> +            bytestream_put_byte(&buf, avctx->width & 0xFF);
>>> +
>>> +            for (int x = 0; x < avctx->width; x++)
>>> +                float2rgbe(s->scanline + 4 * x, red[x], green[x],
>>> blue[x]);
>>> +            for (int p = 0; p < 4; p++)
>>> +                rle(&buf, s->scanline + p, avctx->width);
>>> +        }
>>> +    }
>>> +
>>> +    pkt->flags |= AV_PKT_FLAG_KEY;
>>> +
>>> +    av_shrink_packet(pkt, buf - pkt->data);
>>> +
>>> +    *got_packet = 1;
>>> +
>>> +    return 0;
>>> +}
>>
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